Photoresistor Volume-Modulating Tremolo: Design and Function
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- čas přidán 6. 08. 2024
- In this second of two videos on Tremolo design and function, the Photoresistor (Optoisolator) Volume-Modulating-type of Tremolo is explained in basic terms. The presentation includes diagrams and narrative to clearly describe the circuit design, tracing of the circuit pathways within a Fender Deluxe Reverb schematic, visual demonstration of varying voltages, resistances, and wave forms within a functioning Tremolo circuit using an analog volt-ohmmeter and an oscilloscope.
If you enjoy videos featuring vintage amplifiers and jukeboxes, basic electronic theory and circuitry, and unusual electromechanical devices....all explained in a sometimes unusual but understandable way....then please subscribe to my channel. You will gain immediate access to over 100 videos, and you will be notified each time a new video is posted. Thanks !!! - Hudba
I have spent an embarrassing amount of time "fixing" the optocoupler... until I watched this video and found out that a footswitch has to be plugged in for the tremolo to work... Thanks uncle Doug!
Join the club, Balint. I've done exactly the same thing......more than once :(
Congrats on 1 million. !!!
I just picked up a Strobe Tuner, its a Conn from the 1950's they seller said it didn't work. So i got it super cheap. took it apart and it has those kinds of bulbs in it. I made a few tweeks and cleaned it up and wham...it works...But the display is difficult to make out.
but thanx fo all of you vids, I watched them all and refer them out to other Tube Heads. this kind of info is priceless.
Rusty is pretty smart, he stays out of the drama !
Thanks so much, GH. Rusty and I are still hung over from all our celebrating :) Since he's almost 120 (in dog years), Rusty has definitely learned to "pace himself".
The kitty mop surfing is great!
Thanks, Jonathan....glad you liked it :)
You, my friend, are very clear and eloquent in your exposition.
You have helped me, at a distance, in the repair of an amp fail.
Thanks for your infinit generosity.
Cheers!
You're welcome, Rodrigo :)
Very impressive video and an even more impressive achievement!
Hard to believe that you accomplished 1 million views over 7 years ago!
Wishing you another great 7 years,..... (or more)!
Thanks twice, Dennis :)
You are an invaluable resource and inspiration to builders and tube amp repair techs .Because of your easy to follow instruction and sharing of this knowledge I have been able to build and repair quite a few amps in the last couple of years.It is something that I enjoy a great deal and should have perused long ago; but did not have the resources until I found your channel.
Subscibers will forever owe a debt of gratitude for you efforts to preserve this technology
Wow, thanks so much for your very nice comments, OC. We're glad the videos are helpful.
Thank you for another great video!
Top video, thanks very much Doug for all the good information, really appreciate it.
Best wishes to you and Rusty. John.
You're quite welcome, John. Rusty and I wish you the very best :) ^. .^
Congratulations on a million views! Another outstanding explanation. Rusty's camera work was top notch and the dramatic pointer action really brought it together. :)) Jack's mop surfing is brilliant.
Seriously though, thank you for taking the time to do such high quality videos.
You're welcome, Andrew, and thanks for acknowledging this long-anticipated milestone. We blushingly accept your very favorable appraisal. Thanks so much for your continued support and input :)
Another solid tutorial!
Thank you.
You're welcome, Amo. Glad you liked it.
Great video, Doug. Well explained, nothing more to say here, just Thanx!!!
You're welcome, TC. It's always great to hear from you. Glad you liked it :)
Congratulations on your one-millionth views. For the subjects your are showing this is an extraordinary number, and we all appriciate your way of showing complex technical things. I like the video, your are also transforming your style including more technical helpers (e.g. oscilloscopes etc.) which makes things easier to explain.
It seems Rusty gets a bit jealous on the cat, seems he is grown out of the mopping excersice.
Keep it up, an go for the second million.
Thanks so much, TM. Rusty and I are glad to hear that the videos are clear and helpful. We are indeed trying to step up the technical aspects of our presentations. You're right about Rusty on the mop......you would probably get a hernia just trying to move it around :)
Uncle Doug, thank you for once again making great and accessible videos for us hobby amp tinklers out here. And congrats on your 1mill views.
All the best from Norway :-)
You're quite welcome, Jan. I can only make the videos, but it's the viewers who made the million views. Thanks so much for watching :)
Imma ampaholic?!?! I AM an ampaholic! The first step is acknowledgement. Thanks much Uncle Doug.
Greetings, Patrick. Yes, we all share in a common addiction. Fortunately our Twelve-Step program includes plenty of acquisition, hoarding, soldering, circuit testing, celebratory beer guzzling, guitar thrashing, and late-night neighbor alienation :)
Loving your videos! You have a great talent for explaining and your videos are highly addictive, I keep watching video after video, there is so much information, and it's made so easily accesible by your great explaining. Thanks alot for putting out these videos
You're welcome, Fred. Thanks for your nice comments :)
Outstanding video as well all the others I have been watching over the last 3 weeks. Thanks Doug. Your teachings of tube technology is the best I have ever seen along with the use of opto's in this design, Thank you as well to Rusty and now Jack!! There help is amazing as well. I am sure Rusty knows how to use the soldering Iron also, even with out thumbs?? haha!
You're welcome, Tony, and thanks for your very kind words. I really appreciate your viewing of the videos and hope they all make sense and are helpful. Rusty is the "brains" of the outfit and very talented on guitar and soldering iron, but Jack definitely has more energy :)
Thank You Uncle Doug!!
Another great video, congratulations on your nth view, I must say mrs tbdalva and I watched and enjoyed this video on our big screen, she commmented on the Fender diagram and how artistic it is, I agree.
Thanks so much TB, and greetings to your Mrs. I'm glad you liked the diagram. When I taught school, I always wrote notes and drew diagrams of organ systems, atomic structure, etc. on the board. It always seemed to make the subject more palatable and the presentation more effective.
Thank you for this, you've given me an idea for a project using chips and opto-couplers.
You're welcome, Franko.
@@UncleDoug OMG!!! Ive just spent all day, (got up at 6am), designing, (on paper, old school), a tremelo circuit using a NE555 IC and an Opto-coupler. Then built it on a strip board PCB. It only bloody worked first time. That is a record for me!!!. Normally I spend a week or so trouble-shooting. I'ts now 6:40pm. Day well spent. Thank you again for the idea.
@@frankowalker4662 You're quite welcome, Franko. Congratulations on your successful project.
Looks like all the fame has gone to Rusty's head! What can you do? So much talent in such a handsome dog.
Its great to see the ingenuity that went into this amp. Who would have thought to use a blinking light and a photoresistor for a tremolo effect! Its also great to see a kitten surfing on a mop! Love the detail, love the test setup. Great work.
Thanks so much, Russell. Glad you liked the video. Don't be fooled by Rusty's "screen persona". When the camera is off, he is a creative dynamo :) Jack, on the other hand, is more like the Tasmanian Devil in the Buggs Bunny cartoons.....hyperactive to a fault.
This was great, thanks for a logical, comprehensive approach. This circuit isn’t working on a 72 twin reverb I purchased recently. With this info I should definitely be able to find how it’s failing!
You're welcome, Dustin. I hope the video is helpful and your repair of the TR is successful.
Thanks for these videos. BZ
You're welcome, BZ :)
i missed the first one. damnit. now I gotta go back and discover the loop. incidentally, about to build a tremolo pedal for a friend. sure it's paint by numbers but it's still fun. congrats on all the views! your vids are knowledge gold.
Thanks so much, MH. It's always great to hear from you :)
This is fantastic stuff! Thanks again, Doug!
*Seriously thinking about implementing a software amp-sim...*
You're welcome, AQ. Glad you liked it. The amp-sim idea is fascinating....I would love to see your take on the concept.
There are plenty out there already. I'm a big fan of IK Multimedia's Amplitube. www.ikmultimedia.com/products/cat-view.php?C=family-amplitube But I have a few ideas of my own. Probably something a lot smaller, more affordable, but more user-customizeable. A "roll your own" amp sim, if you will. :)
Happy 1,000,000th
Love the cat on the mop :-)
Thanks so much, Mark. Glad you liked it :)
22:02 That's what she said! Another outstanding video, Uncle Doug! Thank you
Yes, I too have heard her say the same thing ;) You're welcome, Tim :)
You're the best Uncle Doug.
Thanks, LHR :)
@@UncleDoug I now run a local amp repair service thanks to your videos. Once I was able to understand the basic concepts and language that you teach, it allowed me to read and understand a variety of articles on tube amplifiers and troubleshooting.
@@lowheadroom That's great to hear, LH. Congratulations and continued success with your new enterprise.
@@UncleDoug thank you!
Congrats on the successful channel. The optical system is one that I grasp the best. Very cool. I have a custom kit amp I named "Mr. Big"... and it's got the optic tremolo in it. I remember on the bench seeing the bulb flash during early testing.
Now we just have to figure out the "Harmonic Vibrato"... lol. Thank you brother for your quality information. I'm a recent addition to the amp tech world, and there's a few things I've been working on learning. I'm thankful for your work, and others who want to teach the craft, so that tube amps don't become a lost art. I'm one of the precious few who understands a Tel-Ray Oil can.
I guess the next thing I want to understand better is input impedance. Output impedance I got... but input for the guitar amp, and especially the reverb tank return still has my brain a little shifted.
Thanks, DK. You're right that "Harmonic Vibrato" ala Brownface Concert amp is a real handful. I started reading an explanation and dozed off. I think I'll pass on trying to explain that one :) The shorthand explanation for input impedance is the resistance to ground that a signal "sees" from input jack to first tube grid. There is probably a much more complicated and confusing explanation, but that's what it amounts to. I'll leave the reverb for another day :)
Uncle Doug
Indeed.... I have a custom amp in which the pre-amp circuit mimics closely the Fender 50's princeton. There's 2 input jacks... one with 34k impedance and one with 68k... It's obvious with less resistance, you get more volume and different tone. You can also drive the lower impedance one into clipping pretty easy. I got that figured out because I could play with it. Most of the reverbs that use x-formers are 8 ohm to drive... and 2200ohm or so on the return... the drive half I got figured... the other return end I'm not sure exactly how that flies.
Then we have the SS chip driven verb tanks with really high impedance. Hmm. I'm thankful that I'm at the level I'm at... "Match the schematic, test the parts for spec... test the tubes, and make it work again.
Driving the reverb tank is just like driving an 8 ohm speaker, but the output of the reverb has to drive a tube, which has much higher (i.e. 2200 ohm) impedance. Impedance at both ends of the tank have to match the circuit. Crude analogy alert: The tank is like a socket (used with a socket wrench), it's 1/4" drive (8 ohms) but its work output fits 5/8" bolts (2200 ohms).
You are Brilliant!
You're too kind, SM.....but I'd be lying if I didn't admit that flattery does make it all even more worthwhile :) Thanks so much.
Haha. Blackjacks a natural. Surfs up dude! Great vid. & congrats. 👍👍👍
Greetings, RH. It's great to hear from you. I have to agree that Jackson Paw-lick (named for the famous artist) is a fine addition to the family. The floors have never been so dust-free :)
This was super helpful, thanks! I'm about to embark on restoring my Silvertone 1484, which has a photo-electric tremolo like this one, and I've been trying to wrap my head around how it works.
Jason Thorpe You're welcome, Jason.....glad the video was helpful :)
Uncle Doug Well, I'm making progress on this restoration project, and I figure I might be getting to the non-working tremolo in a week's time. I've had this amp for 20 years, and in all the time I've had it, the tremolo has never worked. I know the tube that drives the LFO is good, but I have the sinking feeling that I'm going to discover that the neon/LDR module is bad, with the most likely culprit being that the neon bulb has worn out. Of course, this means performing surgery on the neon/LDR module, and figuring out the correct specs for the bulb.
Have you ever repaired a neon/LDR module? Any tips / tricks? (Hoping I can use my Fluke meter to determine the peak-to-peak voltage for the bulb -- I'm not particularly interested in trying to figure out what's wrong with my old Heathkit scope right now...)
Here is an excellent article that covers all the details re optical tremolos: www.clarkhuckaby.com/NewVibe/CloseLookVibe.html
Wow, who were the wizards that thought up these circuits !
So thanks again Uncle Doug
And a word of advice to Rusty. Watch out for Jack, Rusty, he's already doing house cleaning, won't be long before he takes over at the amp bench.
You're welcome, BF. I think just about every possible circuit was invented before WW II by engineers at RCA :) Rusty has mixed feelings about Jack: He is proud of his little buddy, but does sense a rivalry in the making.
Superb, precise circuit description. Might also be nice to really slow the timebase near the end to squash the 2kHz a bit and reveal the modulating waveform on the trace. Excellent channel. Congratulations!
Thanks so much for your kind appraisal. I sincerely appreciate your time and interest, as well as your helpful input.
Enjoyed the new video! Congrats on the million views, Love your teaching method, breaking down these projects so even I can learn! LOL! Here's to the next million views.....Extra celebratory bones for Rusty & kitty treats for Jack, the Surf City Kitty...so to speak....LOL!
Thanks so much, Tim. It's good to hear from you. We're all a bit hung over from our marathon celebration, and Jack is still riding the darned mop !!
Hi Uncle Doug !
Yet another top draw video. Brilliant !
I have been thinking of building a simple design valve HIFI amp that would be straight forward build for a competent DIYer ( I think )
I love valve amps but I know they can bite you, if you are not to sure what you are doing and drop your guard.
All the best to you and your side kick Rusty. congratulations on your one-millionth view.
David UK
Greetings, DD, and thanks for your very kind comments. Rusty and I wish you the very best. Be sure to let us see your amp project when it is finished :)
I've recently done a mod to the "bug" by cutting it apart, removing the neon bulb, and replacing it with a 5mm white LED. It works very well, especially if you encounter a tremolo with the infamous "tick", clears it right up!
I'm surprised that the LED could withstand the 345VDC that is normally applied to the neon bulb, Mike. Most LED's I encounter operate on 12V or so. I will keep your suggestion in mind for the next time I encounter a malfunctioning photoresistor tremolo and give it a try. Thanks for your input.
Uncle Doug here's where I got the idea: music-electronics-forum.com/t26384/
Being a fellow "Tremoholic" myself , I've been using mine ('65 Fender Twin clone) heavily for the past week. So far, it's holding up very well. Cheers!
Congrats on the milestone! I know your background is rooted in Fender amps, but I was wondering about the tremolo effect in other amps. Magnatone or Gibson or others. Another request would be reverb since you have a mop surfing kitty kitty. Tell Rusty no one can take his place! Maybe he could break the kitty in on video production, for those rare times he needs his own space. It's a good thing you posted the tremolo videos, I thought I could put a single tube for tremolo in a 40-50 watt circuit. I'm not so sure now. Thank you for sharing. Thankz.
Thanks so much, ATL. The area where I live (The Great Southwest) is a Fender stronghold, and that's the main brand I grew up hearing and eventually repairing. I used Fender amps for demonstration, but the principles explained in both videos are universal, and apply to virtually all amplifier brands as well, including Gibson and most Magnatone amps. Check out a schematic for either, and I think you will recognize the circuit. Magnatone also offered a unique tube vibrato effect that was extraordinary and rather complex, as did Fender in its Brownface amps, like the Concert.
I explained Reverb in an early video (on another channel, before I started my own): czcams.com/video/oL69xjGY3MY/video.html It's not as detailed as the Tremolo videos, but covers the topic fairly well with lots of sound demos. I may make another, more detailed version in the future.
Rusty is very proud of his little "pet" but is rather protective of his position as chief videographer for Uncle Doug Enterprises. Maybe he'll loosen up a little as the kitty matures.
As discussed, a bias tremolo might not be a great idea in a 50W amp. If you really want the effect with this amp, a separate effects pedal may be the way to go.
Doug, I'm helping a friend repair his Ampeg Reverberocket GS-12-R tremolo and watched this fine explanation video. Got a couple questions about neon bulbs: In the circuit you demonstrated, is the bulb always conducting (ie your bulb voltage is always greater than the turn-on voltage over the swing)? Also, on these small neon bulbs, what's your estimate on the flash over voltage, the maximum voltage?
Love the mop surfing. Its good to see that Jack was once an sweet-innocent kitty before he became the delinquent international rock star. Ahh, the days of our youth....
Greetings, Craig. In the Deluxe Reverb, the neon bulb operates at 345VDC, so they are definitely high voltage devices. As to the maximum voltage, I have no idea, but will bet that they are very forgiving.....probably allowing a wide usable range of voltage. In the past, rather than experiment with bulbs, I simply order the exact replacement from Fender (on Ebay).
Big Congratulation on your one million views. Give Rusty a pat on the head for me.
Thanks, Bobby. Rusty's contract stipulates that he gets at least one head pat per hour, but I'll give him one extra and say it was from you :)
Uncle Doug
:)
Congratulations on the views! I've enjoyed your videos for quite a while now, and I hope you'll keep them coming!
I was pretty surprised by this one. Compared to the more "modern" signal chains I'm familiar with, it struck me as odd to have a volume modulator AFTER a reverb. Is this more a limitation of tube circuitry, or just one of those concepts that inevitably changes with time?
Thanks so much XC. Glad you enjoy the videos :) To me this arrangement makes good sense, particularly with an electromechanical reverb tank (that must be driven hard to function). In this arrangement, the volume-modulation affects all parts of the music signal equally, whether reverb is present or not. If you modulated before the reverb, the lower volume input would probably not drive the tank, so rather than a simple volume fluctuation of the mixed signal, you would also have modulation of the reverb effect, which would probably not sound good. This may not be an issue with modern, synthesized reverb effects.
You're probably right. But with the modern methodology you would have to overdrive your tubes, and then mic the output through a synth reverb and out again through another amp, or into a DI box for recording purposes. It's messy. But running a synth reverb between guitar and a tube amp, then trying to overdrive the amp... well that's just a writeoff.
I know this is an old thread, but could you please do a video analyzing the univibe circuit? Thank you for sharing your knowledge. I have learned so much from your videos.
I will keep your suggestion in mind for the future, Hey.
I did an awful lot of tripping when I was a kid, and I gotta tell ya, I can see some rather interesting things in that oscilloscope.....
So did Rusty, I guess. He insists that he sees the devil wandering around in our neighborhood sometimes......but its just the dog catcher.
Uncle Doug The dog catcher IS the devil!
Watched this one again, thanks for posting.The ticking in my Deluxe Reverb is driving my nuts.Side note, have you heard the band "Los Straitjackets" , I think you will like them.
+tbdalva You're welcome, TB....glad you liked it. There are several Internet sites that discuss the ticking issue and offer suggestions for remedies. You might want to check them out. Part of the problem is the high voltage required to illuminate the neon bulb. Good luck.
Uncle Doug, great explanation on Fender LDR tremolo function. I've looked all over but can't find the link to the part 1 that you referenced (phase shift oscillators). I'm troubleshooting excessive noise in my 1970 twin reverb v
I believe this is it, Darrell: czcams.com/video/1kV2nz4-fXw/video.html
Doug, I found it. It was indeed the 1967 Princeton Reverb video 3. You strapped a couple of extra 1M ohm resistors across the existing 1M ohm resistor coming off the plate of the oscillator tube. Unfortunately my circuit on the Bandmaster uses a photo resistor and has a 10M ohm resistor coming off the plate of the oscillator tube. Not sure if reducing that value will increase the intensity but maybe I'll try that. Thanks!
Let us know what you discover, Obe. It would be useful info.
Photoresistors are also really great for compression. You basically use them in the signal path, in lieu of whatever diodes one would normally use.
This sounds like a rather unusual use for photoresistors, Adam.....are you sure you're not having an oscilloscope flashback :)
Uncle Doug So, I may be a little off in my description, and in my attempt to correct it, I'll still probably sound less than coherent. I think it goes something like this.....signal between gain stages is split to pass through a photocell and a light bulb of some sort (could also be an LED), and the more signal the bulb gets, the brighter it gets, and the higher the impedance of the photocell. There is also another type of circuit that only uses a bulb, which acts as a variable resistor, stepping harder on the signal as it heats up.....I think the bulbs inside a stock AO-44 are used for this, but don't quote me on it.
I believe that the AO-44 bulbs act as ballast resistors to curtail high signal current flow, exactly like the light bulb current limiter many of us use when working on amps. This really isn't the same as the optoisolator in the tremolo, in which the neon bulb gets brighter, causing the resistance of the photoresistor to decrease.
Yea I was looking for an optical compressor a few weeks ago but I never did pull the trigger on anything.
Uncle Doug muito boa instrução do funcionamento tremulo muito obrigado
você pode responder em inglês de preferir baixei muitas aulas do Sr.
sempre que posso vejo suas aulas sobre amplificadores um abraço mestre
Thanks you very much, Jorge. I appreciate your kind words and hope you continue to watch and enjoy our videos :)
Congratulations on passing the millionth view milestone :)
Jack the cat is cute, as most kittens are :)
Rusty's surely become an executive producer, I bet he's smoking cigars and counting the money only nowadays ;)
But (and it's a big but, with a single "t"), when will we see Uncle Doug in person, so we could put a face to the voice... and hands? Do we have to wait for some other special occasion? Or do you plan to continue the career as a hand model only? ;)
All the best from Poland!
Greetings and thanks, Stan. It's always great to hear from you. Rusty is obviously spending a lot of his (substantial) salary on steaks and whiskey, but is not allowed to smoke in the workshop :) I have not appeared in any of my videos largely because I am fearful of being swarmed by groupies when I shop at WalMart :) Seriously, I'll keep it in mind for a future video.....maybe at Halloween :))
Another great tutorial Doug and Rusty and jack the cat provided the extras.
Now why would Fender use two different types of tremolo circuits in two low wattage amplifiers? It would seem that cost would definitely be a factor but would there be an advantage to use one over the other when being used in these lower wattage amps?
Having owned two Sunn amps, one with tremolo, I went back through the schematics of the 40 Watt Solarus and found it did indeed use the photo/resistor circuit. Very interesting. Now I wish I could get my hands on that old amp if I could ever figure out where it is.
I enjoy all your tutorials especially since when I attended school for electronics, there was one chapter devoted to tube amplifiers and was very generic in nature.
+John Zook Thanks, John. I believe that Fender used the output tube Bias Trem in the Princeton and below (in size), and the Photoresistor Trem in the Deluxe Reverb and above. It's best not to use a Bias Trem in more powerful amps due to the stress it puts on the output tubes.
Hi Uncle Doug!
Congratulations to over one million views and Thanks for posting all fantastic videos!
I have a Deluxe Reverb (AA868) that has an issue with the tremolo.
At first it didn't almost work at all, but after changing the three filter capacitors you mentioned, plus the optocoupler and the 12AX7, it sounds good. The problem is that it doesn't start oscillating right away when it has been turned off for a while. But after having it on for around 30 seconds or so, it starts oscillating by itself and works fine until the next time I have it in off-mode long enough. It seems like current (or temperature) has to build up somewhere to get things started.
Do you have any idea what it might be?
Thank You / Patrick
Sorry, the circuit is AB868 of course.
Greetings, Patrick, and thanks for your kind comments :) Re the "reluctant tremolo", besides the three capacitors (they are not actually "filter capacitors", which are electrolytic), the values of the resistors in the loop must be (reasonably) accurate also. You should check and perhaps replace them. Another key factor is the oscillator tube. For some reason, some tubes work better than others. You might consider trying some other 12AX7's in its place. Final suggestion....are you sure your footswitch is making good ground contact when closed? These switches sometimes lose their internal continuity. You can test this with an ohmmeter or by simply eliminating it from the circuit and grounding the RCA plug that it plugs into. Good luck.
Uncle Doug
Greetings Doug! Thank You for your reply and much valuable tips!
Yes, correct regarding the capacitors, I was more thinking of them as ingoing capacitors in a hi-pass filter :-)
I will check these things and keep you posted if I make any progress.
Best wishes to You and Rusty from Sweden!
You're welcome, Patrick. Best of luck :)
I remember those strange neon-photo resistor circuits used on the earlier amps. it's all coming back to me now.
Now the only photo resistor I see nowadays, are used for shutting off the yard lamp post light bulbs.
I like the 'cat intermission'.
SuperCarver2011 Yes, and coincidentally the PR in my yard post lamp recently failed. Repairing it should be an interesting project. Judging from your icon photo, you are a cat fancier, as are we. Even Rusty seems to enjoy watching Jack (the cat) mop surf :)
Uncle Doug I've had to replace mine a couple of times over the years..harsh Canadian winters, I guess
and the UV tends to cloud the plastic lens. Mine just failed last week, after a few years. Got another one at H-D and installed it. Working fine. These photocells have some kind of triac that craps out eventually because
it was supposed to handle up to 300watts but I've been using a 13watt CFL for years..they just don't
make these things like they used to.
yes, I have a couple of cats, and I support the cat rescue. I was a carver, for a few years and carved some
half size cats to give to my friends and family and as prizes for the annual cat rescue motorcycle ride.
I'll probably go to HD today for a new PR module. This conversation got me thinking about the need to replace it.
We love cats and dogs.....and all animals....maybe too much. Saving them can become an obsession if you're not careful :)
Uncle Doug I don't do the actual saving, that is up to the ladies who run the nokill shelter..I provide donations
every 3 months which is tax deductible.
More power to them, and to you, for your continued support.
"MOP SURFING!" LOL! TOO CUTE!
He's outgrown the mop :)
Doug, I'm working on my 1966 Bandmaster head and trying to beef up the tremolo. Right now the intensity pot doesn't kick in until around 5 but the oscillation works very well. I put in new pots for both the speed and intensity as well as the photo resistor and changing the 10M ohm and 100K resistors. No appreciable change in the intensity level. Still very anemic. I remember seeing one of your videos where you made some change to the tremolo circuit that really beefed it up but I can't remember which video. What do I need to look for? Thanks for alll the great instructive videos as well!!
I recall the tremolo circuit change, Obe, but not the specific video. Odds are it was in a Princeton Reverb, perhaps the '67 model that I had to restore.
Do you recall what the mod was that you made to the circuit?
Are those dark blue caps on the circuit board ITW? I found several of those caps, unused, in electronics lab one time and learned they were used in a lot of silverface era amplifiers. The ITW stands for Illinois Tool Works.
The amp is all reassembled now, but I believe they are ITW caps.....frequently used in SF Fender amps, as you stated. Thanks for your input :)
Congrats Doug and Rusty...1,000,000.00 Hits.... Did you two ....ever think you would help all of us learn ....or re-remember... what we knew or never knew....I believe you two are a bit of a Miracle ,,, Best Wishes......You should be so Proud!....And I personally am very thankful......!
Thanks so much, William. Rusty and I owe it all to our loyal viewers and subscribers, and promise to keep improving our video essays.....so, stay tuned :)
Uncle Doug I can't imagine how!....You and Rusty are as good as it gets. I'll always be tuned in! You should be funded by Bill Gates over hyped "slush fund". .......Maybe Kahn Academy..............wait that is Bill Gates!!!. You're teaching " Theory" ...not a bloody Hobby! You are a "You-Tube" Treasure!!!................ and I mean that! You teach............... as if you teach them not! .............. 1,000,000,00 of us SLOBS...... Hah!! keep it comin'! ....... Bill
We will, Bill. Thanks again for your support and very kind comments :)
Uncle Doug You're a Miracle...[.every comment answered ...man please! ] .....You're a Miracle....a Bloody Miracle !
Just 1 more of your 1,000,000.00 appreciative students.....
***** Your "tube" tutorials are particularly useful ..really outstanding.....I must have run them in the kitchen..10 X times on my Kindle by the sink......cleaning up ....learn and memorize some tube theory while cleaning up...,,,,,,Hah!. How sweet it is! ...Kitchen drudgery was never so sweet,,, Hah! (No wasted time.....except to rerun parts between spoons...Ha!)!
Thank You for this nice explaination video ! That would have been nice to see the actual modulated 2khz waveform envelope (slow scope time base). It looks like as many Fender LCR based tremolo that the final 'to the speaker' signal envelope is not sinusoidale anymore but bumpy... Isn't it ? I'm tryimg to modify a Fender Deluxe reverb LCR based to a direct drive to the output tubes like a Vibrolux design which has a smooth sinus envelope.. What do you think ?
Your project doesn't sound feasible to me. The Vibrolux tremolo modulates the cathode of the first pre-amp tube, while the Deluxe Reverb uses a photoresistor to modulate the signal volume sent to the phase inverter. It's apples and oranges. Good luck.
@@UncleDoug Thanks for your reply. One question though.. Is-it possible that 'most' photoresistor based Fender tremolos produce 'bumpy' envelopes on the final signal to the speaker. The LDR's NEON lamp nature is that it is completely OFF then ignites sudenly on all tremolo cycles for any sufficent voltage across it then shuts OFF also sudenly. This cannot produce a smooth rising/falling envelope like a sinusoidale one does. The direct drive to output tube's input grids with sinus shaped waveform can do that. Am-I missing something ?
You Solved it lol awesome
Next up mop surf lessons.
Jack is the Master ;)
Congratulations on your channel.
Don't tell Jack how popular cat videos are, he'll want to renegotiate his contract.
Thanks, Franky. It's always good to hear from you. Jack is such a scoundrel that I fully expect him to end up running the whole show within a few months. Rusty and I will probably end up being his catbox crew :)
Greetings Uncle Doug! I can't thank you enough for these videos. I'm currently fixing my Fender Super Reverb with knowledge gleaned from you lessons. I have a question about that 10uf cap and 3.3M resistor on the dry line. Doesn't this allow only very high frequencies to pass? It seems drastic. Why's going on there? Give my regards to film-maker-extraordinaire Rusty The Dog and Jack The Wonder Cat. And again, thank you.-Rick
I don't have a schematic handy, Rick, and I think you mean 10 picofarad cap, which does indeed restrict the passage of all but fairly high frequencies to the reverb tank. This is because the reverb tank works well with high frequencies, but gets muddy and unpleasant with low frequencies. The lows still come through the "dry" circuit to be mixed with the predominantly high frequency "wet" signal from the tank.
I have a question Uncle Doug, I have a 1969 drip edge Super Reverb, has the most amazing, studio quality tremolo ive ever heard. I sold it last year, Fed EX destroyed the cabinet, knobs and the faceplate. They paid the insurance and sent it back to me. Could I pull the tremolo circuit from the amp and put it in to a stand alone housing so I can use it on my pedalboard. If this could be done, how would i power it and how would I find out how many volts it uses without damaging it? Thank you! Great videos keep em up!I
The answer to your question is quite complex.....way beyond the scope of this type of communication. Your best bet is to watch my tremolo videos as well as others on power supplies, circuit voltage demands, etc. and figure this out on your own. It is definitely possible, but would be a challenging project. Let us know if you do it, and how it turns out.
Great description and explanation. Do you use an isolation transformer when working on these amps? If not, isn't chasey ground floating? Just curious because I saw your scope grounds connected to the chasey. I know about these things but are not conceptually complete in my mind thats why I ask.
+John Miner Thanks, John. No, since the circuit has a power transformer, the chassis is already isolated, and since the high voltage circuit uses the chassis as part of the circuit, taking B+ measurements relative to chassis ground is the way to go.
+Uncle Doug That makes sense. Just a note, your description in another video about ac/dc being able to coexist in the same line which seems obvious but its not finally led me to understand the function of coupling decoupling and bypass capacitors. Cheers for that!
Thanks, John. I'm glad the info was helpful.
Hey Good Buddy, hope all's well..can you touch on what other means of tube induced tremolo there may be,..on my Univox early '70s 60 watt Lead amp with the 6AN8 pentode preamp there was no LED resistor of the likes of this Photoresistor's circuit, anyway not that I can tell I even rebiased and rewired the 6AN8 to the 12AX7's family, it gave me a better Fender's tone so I'm looking to gain favor of the amp's design to give me the tremolo as well, thanks in advance Uncle Doug, btw can't believe it's already May of 2015,..I was viewing your other instruction seminars to catching up and here we are now, time is elusive like on a tremolo circuit's photoresistor(???)! Oh yea, Ampeg made a pedal with no more than 8 pieces and it had one knob on the pedal but it had a discrete trimmer and with tweaking of the two I got tremolo,vibrato,and two to three other similar effects, really cool pedal,very rare it was called a Tornado, very few were made possibly by Dan Armstrong himself. So if that pedal could accomplish that some of effects with just 1 to 2 transistors etc figured a tube could do the same maybe with a 6CG&/6FQ7 driver and so on,Thanks! Happy Millionth Wow!
Nelson DeJesus Greetings, Nelson. I have also posted a separate video explaining the Bias Modulating Tremolo, which, I believe, is the type you mentioned above. Please watch it to see if it answers your questions.
Pop Quiz: What type of reverb was used by Rusty's Band? (13:40)
As I recall, he was using a BF Princeton Reverb for this performance :)
In this video you show oscilloscope images of the phase shift oscillator output. Exactly where are you probing to get these sinusoidal images? I don't get sinusoidal images on my oscilloscope when probing around the the phase shift oscillator. However, the tremolo circuit is modulating the output signal at the expected frequencies.
As is clearly stated in the video, a 2KHz signal is injected into the input of the amp circuit. The probes are on each of the output tube grids.
Hi uncle Doug, I have a vox ac 30 1973 with top boost & im getting a constant hum when switched on i changed all pre amp vales but no change ,thanks Trevor (uk)
Trevor Clarey Greetings, Trevor. I made a video to help you determine the cause of the hum, based on whether it is 60Hz or 120Hz (in the US.....your frequencies will be different, but the principle is the same). Check it out and see if it helps. Best of luck :)
haha nice i had a black cat named jack,black cats are always awesome
We had a black cat called Jet. He'd sit on a high shelf, wait for ANYBODY to walk past and jump on their head and start scratching and biting. We sent him to a friends farm.
He would attack sheep and try to have sex with chickens. He was a total psychopath.
@@frankowalker4662 hahahaha ! Thats fucking awesome. Legend
Hello, Can you please help me. I have a Fender Quad reverb and the tremolo causes the volume to drop when you turn up the intensity all the way. Also the sound becomes compressed and it is kind of slow to react. I have replaced the filter caps with F&T's and all of the tubes with new JJ's. I also changed the oscillator, new .01 600v caps, ( I'm going to change them all but the others are on order still.) So I need to know what would make the amp volume drop and sound compressed. thx
I have never encountered this problem so I would just have to guess that there may be a partial short to ground when the Intensity pot is cranked up. Use your ohmmeter to verify this and to find the cause of the partial short.
Hey Uncle Doug
Do you have any particular place that you buy tubes from other than finding them in old units that you get from garage sales and such? Also what about input/output transformers and chokes, tube bases, terminal strips and other misc stuff used to build an amp? I would really not want to buy old vintage equipment just to dismantle it for parts. Since I am going to try and build an amp ground up in more of a steam punk theme it would be a shame to destroy old classics for parts.
I understand and appreciate your reluctance to dismantle old equipment. I currently have some old tube amps stashed that are simply too nice to dismantle. I have no idea what I'll do with them :) I get new and NOS tubes and chassis components from Antique Electronic Supply in Tempe, AZ and I get all my new chokes and transformers from Triode Electronics (generally Classictone brand transformers).
UNCLE DOUG< what frequency is the LFO at? 30hz or lower because when measuring lower frequencys on an oscilloscope it wont display a low frequency waveform because its so lower, all you will see is a moving electron beam DOT moving very slowly. Anyway on the oscilloscope to get a stable low frequency waveform because I have to use a frequency counter to measure lower frequencies LFO oscillators because I can't view them on an oscilloscope. How do you measure these LFO low frequency or you use a frequency counter or an oscilloscope?
I don't actually measure the number of oscillations, Bill. All I am concerned with in a Tremolo is its depth and speed.....as determined by my ear.
@@UncleDoug but lets say I wanted to measure the LFO frequency, how about I do this to make sure the LFO frequency is not "drifting" or is the correct frequency. The LFO frequency is so low that the oscilloscope is hard to display a staple waveform.
i was wondering what the reason for a photoresistor tremolo with very low intensity (athough turned up to max) is? bad tube? or is it just common that the tremolo is not so intense on a Fender pro Reverb...?
thanks for all the interesting! videos here.
Weak tremolo is most likely due to weak oscillation in the feedback loop, Theo. Check the values of the three oscillation caps, resistors, and try different oscillation tubes. The Pro Reverb should have a strong tremolo.
@@UncleDoug thanks a lot👌
You should start a school about amps and electronics!
Pablito Ron Thanks so much, Pablito. Just think of our channel as an Internet Vintage Amp School......no homework, no tests, but hopefully it helps you to learn.
In the example circuit, what purpose does the 2.2M resistor between the negative bias and footswitch accomplish? Is this a critical part of the tremolo circuit or a byproduct of something else?
It's my understanding that the wire containing the 2.2Meg resistor injects a signal into the oscillation loop to initiate oscillation when the footswitch grounds the circuit. The resistor modulates the voltage to prevent a loud "pop" when this happens.
@@UncleDoug Thank you very much. I wasn't sure if it was an elaborate grid leak or something. The negative bias through me for a "loop" ha.. oscillation.. nevermind. This makes sense. Thanks again, I appreciate it.
What is the purpose of the connection from the negative bias supply, through the 2.2M resistor to the vibrato pedal/ oscillator input. I do not see that connection on the Princeton circuit you went over in the first video. I have seen this connection labeled 'oscillator kick starter' (or something like that)., on the internet. Will this circuit work without that connection?
I would like to use this circuit in an amp I am building, but the power section is running cathode bias, therefore there is no negative supply.
I too have heard that the 2.2M resistor was to kickstart the oscillator. Yes, it will work just fine without it......most amp circuits don't have it.
@@UncleDoug
After further research, I found out that without a kick start circuit, the oscillator may take minutes to start. I also found out there's another way, by connecting the middle resistor of the phase shift loop to the cathode, instead of ground.
See the Fender Vibrolux 6G11 schematic.
Also a great technical description of the circuit can be found here:
www.aikenamps.com/index.php/designing-phase-shift-oscillators-for-tremolo-circuits
And here
www.valvewizard.co.uk/trem1.html
Note the LED indicator circuit at the bottom.
@@scottbc31h22 Excellent information, Scott. Thanks.
I have a Vox Cambridge 30 twin reverb that suffers from what is known as "cambridgitis". I have replaced the opto-cupler with 2 different brands and have yet to get this amp to function properly.. Can this circuit be by-passed? I never use the tremolo anyways and love the sound of this amp?
Morris Frady I took a quick look at a schematic, Morris, and it appears that this amp is primarily solid state, with a single 12AX7 preamp tube. I work only on vintage tube amps and am not well versed in hybrid circuitry, but wonder why bypassing the tremolo circuit would be necessary. In every amp I am familiar with, you can simply turn down the Intensity setting and mute the tremolo effect.
Thanks for your Comments Doug, but from what I understand about the way this circuit works is,, when the opto goes bad it automatically defaults to the low side of the volume due to the LED not flashing any more..That causes a constant power loss..As far as the tremolo pot goes,, it has no effect to the sound at all.. Right now it is setting in a corner.. Thanks again for comments..
What a strange circuit....in which the failure of an opto-coupler can affect the entire amplification process. This is why I stick with vintage tube amps :) Here is a site that discusses the problem and its "cure": sites.google.com/site/voxcambridge30repair/ You have probably already seen this, but if not, I hope it is helpful. Good luck.
That's really old hat. I am looking for information on the old Gibson and Ward's Airline tremolo LFO PENTODES (usually wired as a triode that runs to the screens on the power tubes, and usually uses another triode for positive feedback), so totally different from this tremolo design, and it doubles as voltage regulator in some amps like the GA40.
I'm sorry to bore you, Seth. Hopefully you can find the information you seek.
@@UncleDoug We still love you, my man! You had to have been a good professional teacher! If not, you sure missed your calling. We have got it! It's a very weird one, and it had been miswired. It used a 6SN7 triode to feedback into a 6V6 and create oscillation with the NON-INVERTING signal from the 6V6's cathode follower with some of the 6SN7's signal oscillating with an INVERTED signal fed back into the 6V6, with usual positive feedback to start and sustain the oscillation. That signal wobbles the cathode bias resistor's value. The old 2P3T 3 speed switch is GONE now. I replaced it with a dual ganged 1 meg linear pot with two 2.4 meg-Ohm resistors wired in parallel to get two 705K Ohm ganged pots so it's variable speed now and not just slow medium or fast. The Wards LFOs are just pentodes wired for triode but the same basic architecture as most Fender/Ampeg/etc. LFOs. The Gibson one is a real oddity, and nothing else sounds like it. We also added an intensity pot. There was a VR for a grid leak, but adjusting it killed the oscillation completely. I do a lot of the Magnatone amps. This was lots easier than chasing that two channel pitch shifting and panning stereo mess that Magna/Estey used.
That 2205 scope reminds me, I need to put a new battery into my 2245B lest I lose the programming in it, and make calibration into an impossibility.
I found a tremolo pedal that uses this type of circuit, with an led and photocell, but for the life of me, I can't remember what it was and can't find it in my youtube history.
It was a cheap pedal and the guy that opened it was surprised to find an led and photocell inside. I'd love to make one but I think I'll just end up buying an optical tremolo pedal at some point. I guess it could've been the chorus/vibrato pedal I ordered but I've still not found a video showing someone looking inside of one. 🤷
Good luck with your quest, JC.
I have an issue that is not on this topic, but was hoping you could give me some feedback. I have a footswitch that goes to a 72 deluxe reverb amp. The vibrato switch works fine, but the reverb won't switch off. I changed out the switch with a new carling switch. It still will not work. I get continuity with my multi-meter. The ground wire for both switches has to pass through the new switch, and the vibrato switch works fine, so I'm guessing my solder work was okay. I'm stumped as to why it won't work? Any ideas?
rbauer1632 What happens when you unplug the reverb pedal from the amp.....does the reverb cease? If it does, then the pedal wiring is at fault. If not, then there is a problem within the amp circuit. The reverb pedal grounds the grid of the recovery tube to stop the reverb effect. If the pedal is at fault, then apparently the switch is not grounding the signal wire when it is closed. Check to see if there is continuity between the signal wire and grounded shield when the switch is off.
Uncle Doug I tested the amp with a different pedal and all was fine. So, it is obviously in the pedal. I knew this, but couldn't understand why a new switch didn't fix the problem. Since your reply I tested the continuity again. The vibrato was fine, but no continuity on the reverb wire. Except, I do get continuity on the braided shield at both ends. Maybe this is what I had mistaken for continuity in a prior test. I'm new to this. I pushed the button and do get continuity between the wire and braided shield inside the pedal cavity, and at the other end of the braided shield, but no continuity at the rca plug wire end. Now that I look at it, it looks like someone else may have tried to repair it, because the reverb wire is about 3" shorter than the vibrato wire, which is what I would have done to clip the original connection to the plug and reattach it. If it were up to me I would just buy a new pedal and be done with it, but the original pedal seems to be important for resale value. So, I will try to get a better connection and see if that does the trick. Thanks for your help.
Yes, RB, the shield should make good contact with the chassis of the amp to provide adequate ground to shut the reverb off. This should be fairly easy to repair now that you recognize what is wrong. Good luck.
I'm troubleshooting excessive noise in my 1970 Fender Twin Reverb. I've monitored the signals on the vibrato circuit but they appear to be anything but sinusoidal. Can you give me the link to part one and expound on waveforms of LDR type Fender vibrato circuits? Thanks!!!
If you inject a mono-frequency audio signal into an amp circuit with the tremolo (it is not really vibrato) function "on", you should see the wave form of the input signal increasing and decreasing in amplitude at the same rate as the tremolo oscillation loop. This is the only proper way to visualize the tremolo wave form. The erratic wave forms you are seeing are probably not related to the tremolo effect.
@@UncleDoug When the tremolo is enabled there is what appears to me to be excessive noise and some hum (60 or 120Hz). When I unplug the input to the amp the noise is greatly reduced. I have a high quality Mogami guitar cable but it appears that with tremolo enabled and guitar plugged in I am picking up a lot of noise. Is this normal or can I reduce that somehow? I also noticed upon inspection that the tremolo intensity pot is a 100K linear taper instead of a 50K linear per the schematic. The pot looks original but I'm looking for a 50K to install to see if that improves the noise. I'll greatly appreciate any suggestions. Maybe this is normal for this amp, but without the tremolo enabled the amp is super quiet and sounds great. Thanks!
@@darrellsego1155 Have you tried substituting other tubes in the oscillator position? You may just have a noisy tube.....it's not uncommon, and the effects vary depending on where the noisy tube is located.
@@UncleDoug I substituted in several different 12AX7A tubes in the oscillator circuit with no significant difference. I even replaced the 3 long run wires between the tremolo circuit and the intensity and speed potentiometers with shielded cables, also with no significant difference. It could be that the background pulsating noise is normal with the tremolo enabled since it is varying the gain of the preamplifier circuit. I know that the existing carbon composition resistors are more noisy than metal oxide resistors but I have not replaced the carbon comp resistors yet. I have also read that some users prefer to replace the ceramic disc capacitors in the tremolo circuit with polycarb or polypropylene capactors but I have not done that yet either. Please let me know if you have any other ideas that may help me in reducing the background pulsating noise when the tremolo is enabled. Thanks!
@@darrellsego1155 Without hearing the "noise" or being able to evaluate the circuit in person, I can't offer any further advice, Darrell. It sounds like you are eliminating each of the possible causes, one at a time. I suggest you continue in this fashion. Good luck.
Now I may be imagining this, but I seem to recal that the tremolo effect is not a sinusoidal increase/decrease of level. Instead you get a fast increase in level and a slower decrease. This is born out in your scope image of the tremolo stage output. Has anybody else noticed this?
I honestly haven't ever noticed this, Brian. It's an interesting theory.
my photoresistor lights up but does not oscillate i didnt do it but the caps were replaced the .01,.01,.02.i dont know how long ago if you see this i was planning since it lights up to replace those 3 caps again and go from there.any suggestions would be greatly appreciated mine is a 68 ab763.
Try changing the oscillator tube, PJ.
@@UncleDoug i will and i wanted to let you know i have watched all the videos several times on this circuit.thank you for replying your videos have been a tremendous help
for and my understanding of these circuits
i just now did it and it works thank you i would had never done that it hasnt worked in 30yrs thank you
great video! what would cause it to sound weak? i have a 67 proverb that has very weak tremolo. could be the tube or the resistor itself, i guess. what should i look for?
thanks,
mikeB.
Thanks, MM. You might check the 50K Intensity pot to be sure it's working properly, and try some different tubes in the oscillator position. Some tubes just seem to work better than others as oscillators. Best of luck :)
Uncle Doug
after trying various tubes i've noticed that when i raise the intensity knob that the volume gets quieter?! should i change the 3 caps, the intensity pot, all 3, or look elsewhere? thanks, mikeB
If the chassis is out of the cabinet, can you see the neon bulb brightly flickering, faster and slower in response to the speed control? If so, then the oscillator is working. If not, do you have the footswitch plugged in and "ON" (which is grounded for this circuit)? Are you sure the footswitch offers a good ground when "ON"? If all this checks out then we'll have to look elsewhere in the circuit.
Uncle Doug
i pulled the pro reverb's chassis and hooked up the same footswitch you have. no light at all. i also pulled my super reverb 67 chassis and checked it, but also no light. however, i know the super's vibrato works because i had played it 10 mins. prior and it worked. i let the tubes cool down, pulled them and pulled the chassis, but no light. isn't that weird? now i don't know what to think. guess i'll just do the shotgun approach and replace the caps and the bulb and resistor. still, the super's not lighting is strange. thanks, mikeB
Are you sure the footswitch was in the grounded "ON" position ?? Normally you can see the bulb flickering in the open end of its shrinkwrap covering....as I demonstrated in the video.
👏🏽
Thanks, Emilio.
I’ve got this 1965 Fender Deluxe Reverb and the tremolo has developed a Thumping sound, not a Ticking sound that is common. It thumps in rhythm with the speed. I replaced the roach and also the 12AX7 but no change. Any ideas? Thanks.
It is generally caused by the high voltage required to trigger the neon bulb. There are several cures available on the internet via a search.
@@UncleDoug Thanks for the lead. I’ve done a lot of searching generally, plus on Hoffman’s forums, but not found an answer for the problem with a photo resistor driven tremolo.
@@wsscott72 1.)www.tdpri.com/threads/filtering-out-tremolo-thump-question.1026286/ 2.)czcams.com/video/9GAkTDwp1BY/video.html
3.)www.thegearpage.net/board/index.php?threads/victoria-victorilux-tremolo-thump-help.1278394/
@@UncleDoug As you know, the DR has an optocoupler tremolo, and these fixes all have bias based tremolos. At least that’s what their discussion indicates. So I wouldn’t think those fixes would work.
@@wsscott72 Since #2 was specifically for a Deluxe Reverb, I would think it might apply to your situation.
Uncle doug, I have a Gibson Lancer (GA-35RVT) and my optoisolator lamp is on solid with no flashing. Amp is working great with you mods but the trem is not working.
If the bulb is not flashing then the problem is in the oscillator circuit....check the tube and the values of the three capacitors in the oscillation loop.
Is it important to use a dummy load when scrutinizing an amplifier.
It's fairly standard procedure, WC, because tube amps should never be operated without an appropriate load on the OPT secondary. The dummy load fulfills this requirement without all the god-awful noise....i.e. 1000 Hz at high volume 8>(
Great video again uncle Doug! I see Rusty is still sleeping on the job, I think you should dock his pay!
Thanks so much OOS. I'll add a little NoDoze to his food :)
The amplitude variation looks a bit choppy. I suspect the ohms change of the LDR and Neon combination is non linear and that you can see the amplitude dwell at the minimum level on the scope trace , where you identify the wavy central minimum volume line, the scope x axis time base makes many passes during the signal's dwell at the minimum volume and that leaves the superimposed minimum trace on the display as a tell tail.
The resistance modulation probably is a little uneven, WC, but with an effect like Tremolo, it's probably not an issue. At least no distortion is incurred, as it was in the bias-shifting circuit.
Uncle Doug If you wanted to, you could display the shape of how the resistance changes with a trace on the scope, by placing the ohm meter probe on the top terminal of the intensity pot to supply a DC voltage, instead of the sig gen signal, with the scope probe on the wiper terminal , with the wiper set at half, to display the shape.
An interesting suggestion, WC. I'll keep that in mind for a future project. Thanks for the input :)
Mop Surfing, what a trend.
He was hanging 8 (no dew claws) with the best of them :)
@@UncleDoug Funny stuff.
I'm a bigger fan of Magnatone vibrato. I have a feeling that Leo Fender did too....because he labels the tremolo on his amps as "vibrato"....Then he was forced to keep up the ruse and call the whammy on his guitars a "tremolo" arm. Fortunately for Leo, his amp designs were higher powered and his cabinets were sturdier than Magnatone (who concentrated on sound quality features like vibrato over tremolo). More power and sturdier cabs were more important than a bit better sound for gigging musicians and Fenders went on to legend status while Magnatones went out of business.
Magnatone Vibrato is an unusual effect....some love it and some don't. It's noticeably different from Tremolo, producing a "fluttering" effect (to my ear) somewhat reminiscent of a Leslie speaker (which produces both effects simultaneously). In addition, true vibrato is challenging to produce, requiring a sizable and rather complex circuit, thus increasing the possibility of failure during a performance.....not a great selling point.
Uncle Doug I own twelve Magnatones and in my experience failure is probably less common with Magnatone vibrato than with Fender tremolo. Both use a tube to drive the effect so that's a wash. I have had to replace bulbs in Fender tremolo circuits but varistors never burn out. As for the sound, taste is subjective but tremolo always sounds to me like playing your amp through an electric fan or like a helicopter, while vibrato is more musical like a violin or human voice. And the phasing effects you get playing the amp through external speakers into 3 dimensional space are legendary.
Thanks for your knowledgeable input, Joe.
you reveal Leo secret :)
Hello Uncle Doug, I always love your videos and Rusty and Jack are a great treat. Many thanks for these !
Hi Doug just discovered the channel based on high recommendation from a friend. It's been a huge help as I try to return a 65 SF Super Reverb to its glory. I'm nearly finished but I'm hung up on some tremolo tube voltages on the schematic. I have 450 at the bulb, and 440 at the pin 1 plate. The layout & schematic says it should be 280 vdc. It also says 120 vdc at pin 8, yet I only get 20 vdc. The trem circuit seems to be working normally and all of the other voltages are correct. Can you tell me what voltages I should be seeing on pins 1 and 8?
www.thevintagesound.com/ffg/schem/super_reverb_ab763_layout.gif
I really appreciate all the content you've provided!
+Lothar ThirtyFour Greetings, L34. I'm glad you joined us. Are you sure it's an AB763 ? I looked at an AB568 schematic and it appears that your voltages are a little high, but not enough to worry about. The schematic shows the bulb at 415V and the cathode at 12V. vintagefenderamprepair.com/wp-content/uploads/2012/03/Super-Reverb-AB568-Schematic.pdf Some of the elevation may be due to higher modern wall receptacle voltages. Regardless, if the tremolo is working perfectly, I would probably just test the resistor values in the immediate circuit, and if they check out then live with it.
+Uncle Doug Its definitely a AB763. Still has the tube chart sticker slapped on the inside of the cab. Cleanest original 65 I've ever seen. Thanks for the info! I am looking forward to diving deeper into the channel and doing my own (semi) scratch build soon.
You're welcome, Lothar, and welcome aboard the Rusty Express :)