Fender Champ tube practice guitar amp repair tips How to by D-lab
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- čas přidán 18. 04. 2015
- I thought this would be a simple tube swap. Boy, was I wrong. This amp had multiple issues. Good thing I had the camera rolling. I hope this helps you to repair your classic amp. I work every weekend and nights keeping these old birds running. It is my love. Plus, I enjoy helping out the local bands.
- Věda a technologie
Love your videos Terry. They hold a very special place in my heart. In 1976 I bought a used Fender Deluxe Reverb (black) for $150 bucks from my grocery store job that paid $3.00 an hour. It was not in very good shape, but man, I learned quickly from it, learned to solder, and even started building radios after that. 25 years after I sold the Deluxe Reverb , I bumped into the musician that had purchased it from me. He said that it was still going strong. Keep up the good work, and your great teaching!
Nice video, Terry! You're exactly right on the whole "one problem leads to another" when it comes to tube amps. What was supposed to be a simple fix becomes not so simple. Things get out of hand fast.
One of the best amp diagnostic videos I have ever seen...Cheers to you D-Lab!!!
+Ed Brinley Thanks man, That means alot to me. I do this for fun and spreading the wealth
Always looking for a easy fix sometimes leads to a headache!Your right a little help from Bob always leads to a better end.Great videos,you remind of my high school Electronics Teacher ,always showing you why,how,and the right way to do it.Thanks
Like all of your episodes Terry,sometimes I make a rerun of some old ones like this,keep up the good work,regards Colin.
The old "house of cards" amp repair. Gotta love it. Terry, please do a video of a customer who wants his amp problem diagnosed over the phone for free without you ever taking a look at it.
Have a great week!
Isn't that how amp forums work? LOL!
You are my hero! Please, keep making these videos! I wish there were more people like you in the world who take their time and talent and show the rest of us the tips and tricks that years of experience have over anything found in a book. Thank you!
Byron Fay II Cool deal man, I appreciate it. Yes, I do enjoy making the videos. Will have more on the way. Lots of amps to repair here. TD
Fun video with a great variety of issues that can come from such a simple circuit. Thank you sir, love the final Cabernet touch ;)
thank you!!!! i just bought one of these bad boys and i had so many probs. fixed it up for no cost and it plays like a little dream
Enjoy the Vino . Great videos TXS. From Ireland hello
Sounds like the adventures I've had in a few vintage amps.... I did a Blackface Bassman 50.... and when one thing was fixed, another one cropped up. I've had it working happily in service for a half a month now. I seriously think I finally GOT IT.
Amazing content!!! Thank you!! You are helping me start my journey! Looking forward to learning much more from you. Thank you.
Enjoying your videos Terry.
I've refurbished 1/2 a dozen or so Champs & Vibros and they have all had that 2mfd 25v cap which is also shown on all the schematics beginning with the AA764 Blackface. I've always upgraded it to 50 volts as well. The reason for the high current on the 6V6 is if you check, you'll find that the late 70's and on have PT's with a B+ that's 50-60 volts Over the original specs.
With typical home line voltages running closer to 125v than 117v doesn't help either!
+G Morgan Yes Sir, I really enjoy working on the old Fenders. I have a Vibroverb and Showman in line for repair. The Showman is missing the back panel, otherwise it is stock. I plan to focus mainly on Fender repairs thru next year. Hopefully people will see me as more a repair shop rather that boutique amp building. That market appears to be dying.
Terry Dayton Yes it is! Over Saturation. If you ever need an old Fender schematic let me know I have them all for the 50's & 60's except for say for 1 or 2 of them.
LOL! "El Junkaramus"! TOO GOOD! Please keep 'em comin', Terry.
fantastic guitar test at the end we really get to hear the amp real world!!! thank you!~
At the end of the day, the amp is fixed, and you repaired it. Great Video, thank you.
Good stuff !! I'm getting back into tube amp repair, all these videos help a lot.
Very nicely done; I have run into similar situations where you have a number of cascade problems that must be resolved one by one, patients pays off.
D Lab to D Future😎 Pls keep posing more fix it helps me and motivates me to learn how to fix tube amps...more power wisdom n knowledge to U Sir!!
glad to see I'm not the only tech that can fix and not play
"So you wonder why things get so expensive in the repair shop?" Love it! Cause I work in a repair shop :)
Hey man, Thanks for the donation, very nice of you, e-mail me direct & I can assist with your project/questions. TD
These are perhaps the very best sounding amps that Fender ever made ... BIG statement, I know, what with the likes of the tweed Deluxe and the tweed Bassman and the Vibroberb and Super Reverb and Vibrolux! But this Class A or single-ended design, just sounds incredible to my ears, after 60 years of guitar playing ...
Love this old video...seems much like my amp fix woes...
Never ending battle with seemingly simple things...lol
Great Job analyzing the Champ Terry!
Thanks for the video, Terry! The ending cracked me up, as I was finishing a glass of red wine as the video ended :)
Terry, enjoyed the video. We REALLY need a D-Lab-type shop in my town. Cheers.
Celebrating with Communion wine. Gotta love this guy. 😁
You make very nice videos Terry with various tube equipment. I recently repaired/restored a 1956 Fender Tweed Deluxe replacing the audio output transformer, caps, tubes and repairing the voice coil in the Jensen Speaker. I used "Goop" to reattach the cone and it now sounds great. 73.....
+TheRudydog1 Thank you and also thanks for the repair info. I use goop quite often in the shop. Mostly to adhere caps and power resistors to the chassis to reduce fatigue. Never tried it on a voice coil. That sounds pretty intense! Great keeping these old amps alive. Glad you are enjoying the hobby.
I'm an engineer (BSEE Cal Poly SLO & MSEE SCU) - but choose to work from home. I have a small lab and bought my own software for jobs. I can relate to two things you've mentioned in this video 1) I work three times as much for have the cash 2) it isn't unusual for me to have a glass of nice red wine - I like CA Pinot & Spanish Tempranillo - yummie
Just noticed a Ham call sign in one of your videos - I haven't been on the air in so long that I didn't even notice the got rid of Morse code requirements - I was a Tech Plus back in the day - KD6NCR (my S.O. is KK6ONC)
I worked at Vandenberg AFB in Lompoc. I grew up in the Santa Maria, CA area - known as the Central Coast.
+silvermica Hello, Yes Ham here too. Got my call while stationed at Vandenberg AFB, CA.I hope someday to just run my shop. Problem is, tube repair is really drying up.What software do you use? I normally run Dasylab and some Labview. Mostly data acq and tester controls.Fun stuff, but once again, no money in it around my area. Stuck in corporate America!
+Terry Dayton I bought my own copy of Altium Designer. This is my first time using schematic capture and layout - and I find I do love the control. For design work I mainly use HFSS, Momentum, and ADS. I'm in Silicon Valley so it's somewhat easier to land gigs. On the side I do some software stuff (there's a lot more of that out there).
I got my license in 1992 and had a boat load of fun on 2 meters. T-hunts were especially fun.
Great video. I found it very informative! Even with such a simple circuit, so many things can be wonky contributing to performance issues.
Saturday in the park
Good job Terry, on the Vino.
Genius!!! Loved your video...
I have an old fender video champ... 1970
Still holding up well, but looks like it could ready to go at any point... hope there’s someone around as good as you to look it over!!
Vibro... dang auto correct
Nice video... doing that bias was really helpful also.
Very informative an educational as always, thanks Terry. Cheers, amigo! :-)
Thank you Terry...great vid...you have to be relentless with electronics...cheers
Great video! Always helpful! I have a question, I bought a standby switch for my blues jr and I don't see any videos on how to install, can you help?
I know this is an old vid, but learning cure is always present..Top fix and info..Ed..u.k..😀
Great video! You're so right about one thing cascading into more problems on these old valve amps. But what is a whole lot worse is working on old classic US car. Something that sort of surprised me when working on my '65 Olds Cutlass was that behind the dash is a large (2ft) circuit board that has a big multiplug at one end. The dash instrument lamps etc just plug straight into the circuit board.Any idea how long circuit boards have been used by manufacturers?
You're so right about the underlying problems! I cleaned my 12AX7 pins and sockets and thought wow, it's all fixed! Not. After watching your videos, I found some caps that looked pregnant, one had a piece of rubber about to blow out the end, and another was leaking. I learned there's always more to it than you think! Thanks for all your help!
Cool deal man, It's always best to give them a close inspection. Sounds like you cleared some lingering faults! Good job!
D-lab Electronics yep...sure did! Thanks to you!☺
Just the reason I got out of repairing pianos. "It was just a sticky key!" HA! JUST?!
Another great video Terry! Don't have to give an excuse for the wine drinking cause I would too if they let me at work! Oh and don't listen to the haters they are all just jealous that they don't have your talent!
I love champs great video
Really great video appreciate this so much, thanks, D
I use a 6mm (.253 cal) bore brush used for cleaning rifle barrels, with a tele volume knob glued on for a handle to clean jack socket sleeves. They tarnish with weather change and fuck up the earth to shield connection. Cost less than $10 to make...
Hi Terry ,, love your videos,,
Did you check the plate and filament voltage on that amp.. A 1K bias reisistor seems high for a 6v6gt class A amp. I checked the schematic and the plate voltage should be ~ 350VDC. But even at that voltage the bias should be very hot with a 470r bias resistor as the plate and screen are only separated with a 1K resistor. The Fender tweed champ should have around 330-340V on the plates but the screen sits lower as you have a 10k resistor between them,, so the bias with a ~500r resistor is more reasonable..
To my understanding,, high plate and screen voltage with a high bias resistor value is not the greatest solution for a class A amp...The RCA 6v6gt sheet says ~ 50mA total cathode current at 250V plate/screen with a 5K reflected load, With 315V plate and 230V screen the total cathode current should be around 36mA with a 8.5K reflected load.
+dansk björn Hello, Yes Sir. The owner of the amp plays Harp. He wanted this amp on the soft response side. I should have mentioned that in the video. TD
It's amazing how one issue leads to another in a chain. This has happened to me many times...a customer would bring in an amplifier and describes the symptoms as being just a noisy tube. In the mean time, new set of tubes, jacks, and 5 filter capacitors later the amp is finally working...Oh, I'm sorry, I forgot the bias supply filter cap (which makes 6) :) Then the after everything is working great, the customer cry's the blues instead of playing them. Well, for 75 bucks an hour they can't go wrong...but try telling them that LOL Great videos!!! Keep 'em coming. Frank Ferraro--Audio Craft Electronics
+Frank Ferraro I'm with you man. This situation does happen often. My issue here is, I'd be lucky to get $15.00 per hour. haha
Great video.. I own a '73 Champ myself. What is the difference between input 1 and 2. Is there any...?
One of these days I'm going to drive up there to Michoacan and teach you a guitar chord; in the meantime, you think about which one you want to learn...
Top drawer!!! Thank you!
Nice work, but that is not a lock washer, it is a toothed washer on the input jacks. FWIW, I also will have a glass of cabernet sometimes when I am working on an amp in the evening.
Terry, all you're stuff is great! I recently replaced a 470ohm bias resistor with a 1k on my champ project as you suggested. It will take you about one day to learn to tune and play three chords on your guitar. Just sayin'...
I understanding wy you drinking wine after repair! It's a victory liqued! Santé
Maybe a little vino before the repair is tempting. lol
That sure is a clean champ
Terry-I got my first amp in 1959 or 1960, it was a Fender Tweed,
and I believe it was either a Champ or a Harvard. I know it only had 1
speaker, and I think it was oval. It was pretty small, and of course
basic. I'm thinking of building one and trying to figure out which one I
had, and/or which one is the better choice if there's no way to tell
now which model I had. Do you have any thoughts to help me on this.
Thanks.
I think you'll find that most vintage amps run at a voltage that is higher than spec due to the 9% or better increase in wall voltage ( from 110v to 120v or even more) and will throw cap voltage rating out of spec , that being said what harm is there in having a higher voltage rating for a bypass cap , if the uf rating is the same ?
Hello Terry, have a question, when reading tube data sheets say RCA they give you a "series column and a parallel column. Which column do I read when working on amplifiers?
Thanks
Love this guy!
Great video. Thank you
Terry you crack me up sometimes! I don't know where you live, but I wish I lived by you as you would be fun to hang out with. I recently finished my 1st amp build, a fender champ/early Princeton/Uncle Doug clone. I think it came out rather well. I had initially purchased an old broken Hammond L100 to convert to a guitar amp, but soon realized I didn't know enough about amplifier circuits to do it. I started watching various people (you are one) on CZcams, and well, I think I can do it now. That will be my 1st PP amp. I am making a video of the champ and will send you a link. Let me know what you think. Thanks for making your video's, Tom
+Bucyrus Erie12 Thank man, I try to throw a bit of dry humor into the videos. Love to build and repair the vintage stuff. Sounds like you have the bug now! Have fun with the hobby my friend
Just finished repairing an earl 60's Gibson amp that was a nightmare. Just like this, one problem after another. Finally one problem was really throwing me off - I thought the owner was gonna kill me cuz I just couldn't figure out what was wrong. I put it all back in the case and tried one more time, and whadaya know? It starts working beautifully! The tone controls were dangling about 5" from the power tube sockets instead of being a bit above like when installed - it had me running in circles... There were in addition almost all resistors and caps over 20% out of spec and leaky... I'm a part time fixer, but I'm henceforth gonna be choosy about my repair projects...
Great video, and thanks for sharing!
+Britt Rossman Yes, I understand. I know how those old Gibsons are. Especially if they have the paper/wax caps. Normally I just change them all, don't even bother testing. That is a tough bird. Have not worked on one for years.
+Britt Rossman Some of those old Gibson amps have some unique tubes in them. One has Loctals mixed in with Octals, and Novars. Others have "type tubes" in them, AKA type 80, type 75 and type 42. Those make great harmonica amps. The type 75 has a mu factor of 100, like a 6SQ7, 6SQ7G, 12AX7 or 6EU7, but only one section, and very big plates. I have a stash of modern Amp Ohm wax paper & foil caps. I glue ink jet printed kraft paper on them with contact cement & dip them in bee's wax, so they look kind of original. I do the same with Mallory caps too.
Hi Doctor!!
excuse me I have a Fender Twin Reverb 65 made in 1990 but I have a problem with my amp. the reverb effect does not work at all and I don't really know what I get to do?
do you think is only clean inside of the Reverb Tank maybe have to much dust inside or That is wrong if I try to do that?
and what kind cleaner spray I can use for the amps and guitars controls?
thank you so much!
LOVE YOUR VIDEOS MAN ;)
Terry, any idea what the Fender factory is painting the bias pots with to lock them down? My Super Champ had a dab of red (paint?) holding the bias pot setting from changing. When I retubed the amp the red stuff broke loose easy enough when I rebiased the amp.
I'm guessing automotive touch-up paint or fingernail polish. What do you recommend using to hold the bias setting in place?
Terry, if that bias resistor had not gone up in value and was still 470 which is the correct stock resistor, the idle would be even higher about 57.4 mA. Is this because other component values have strayed over time to cause the voltage drop at that point to have strayed higher over time? Just trying to figure this stuff out, thanks for the great tutorials!
Nice video, good info. You're a funny guy
what was the fix to the triangulated sine wave form?
2uF is actually the correct value for that replaced cap according to the schematic and diagram.
Wow! I always wandered what Ned Flanders does for a living! Great job :-)
Hello, never been compared to that character, however can see the resemblance. Guess I may have to cash in on that during an upcoming vid! Does he drink wine in the cartoons?
Great video,s Terry. Better than NETFLIX!! 😁 Can you show us how to get rid of hum in Fender Vibrochamp amps?
Pretty nice video Terry! Just made me to subscribe! Can you make a video about to poking inside the amp with an oscilloscope to find bad components?
Greetings from Hungary!
andris schóber Hello, Yes, will do. Thanks for the kind e-mail
Which type of signal generator did you use in this video? It looked like the size of an Ohm meter.
Cheers man, you've earned :)
Learn to strum a simple 'C' & 'G' cord...as always great job!
Em & Am. They're easier. And sound that bit winier. (sic).
Recently re-capped a Vibro Champ. It also had a 2uf @ 50v bypass CAP. Mine was located on the first half of the V1.
Looked original to the amp.
Something tells me this CAP was an intentional install.
My amp sounds great after re-capping with 25uf 25v CAPS.
Wondering how many other Champs are carrying a 2 uf @ 50v?
Thanks for the upload.
The schematic for the AA764 shows 25u/25V for the first half of the 12AX7 and 2u/25V for the second half.
The AB764 shows the 10uf. That's the late 70s, CBS, higher voltage Champ schematic. Mine had a 2uf, surprisingly...
Nice interesting video Ted, if you don't mind me asking, for the scope view, where would one hook up the probes, at the speaker + - or before the OT?
+Eric Öhman Hello Eric, connect the scope to the speaker terminals. Just make sure the scope probe neg lead is to the speaker neg or chassis ground.
I never trust lock washers for grounding. Usually the jacks have a ground tab and bridging these with wires to ground is a sure fix.
Spot on
Enjoyed the video, Lighting is a little dim. I sure hope you charged more than $50!! LOL
I have 2 small amps and a pedal I need repaired but afraid to get the bill!!
You can't get too much more simple than a single ended Fender Champ amp. Some of them do have some maddening multiple issues though, especially when someone tries to hot-mod it, and gets it wrong. I have even seen factory mistakes in the pre-1985 stuff. .003uF caps in place of .03. That tremolo circuit never worked right for over 50 years, with that cap in there. Just for fun, take me through an Engl Fireball. I have been through one, and I really just want to see someone else suffer through Engl's inaccurate schematics. Enjoy the mislabeled components, unlabeled components, and various relay circuit lines that go to nowhere, have no IDs and just leave you guessing. Best advice, pretend there is no schematic for it, and work from theory of operation. I don't use an Apmlitex anymore. Mine blew up a Telefunken YL1350 Engineering sample prototype. I happily sold it and upgraded some vintage tube testers & a couple curve tracers with regulated PSUs, and test sockets for use with Kelvin lead DVMs. Now I am working on a PIC based tester, and an Arduino based tester. One of the best investment I made was a good quality, but dated LCR bridge. What a versatile time saver those are. I even bought a cheap Asian spare. I have a 371B curve tracer, and am working on high power RF & ham radio gear too. Anyone with the big power linear amps usually has more money than musicians in these parts. Same with most people who own Marantz Model 7,8 and or 9, Conrad Johnson, Mc Intosh, etc. That work kind of picks up some of the financial slack for the guitar amp work. Musicians here are very underpaid too. The good ones spend their summers in Europe and make 20-100X more for a show.
I like your style! boom!
+larry benben Thanks man, I wont let you down
What spray product do you use on the pots, Terry?
How much does a tube-checking-device cost? Because Im wondering if its worth installing it in an amp.
Doc Terry can we put a Clutch Capacitor to boost d amp over drive much better?!?😅 Hey Doc i watch ur video at work everyday here in our car dealership ! more power Doc...
I have run across plate load resistors making noise several times. Doing your test, the static on the trace makes finding those easy. They make an intermittent static once the amp warms up. There is no other way to test them other than swapping them out.
Lulu you can put a low capacitive cap @ 5 to 10 ufd at needed voltage rating, from the plate to ground. If the noise goes away,then you'll know the plate resistor is noisy!! Always check the input grid for noise first! I have used this technique for years! It works! Good luck on your repairs in the future!!
HELP?!. Sir, I purchased a new Fender Rumble 25 Bass amp, 3 weeks later I plug in, turn on ....and no sound?
Amp makes power up sound at speaker be when pwr switch is depressed. No loose plugs, knobs, and never dropped. Plz help.
Thanks for the video. The best advice was the Robert Mondavi assist at the end. I've got one amp that been on my bench for a couple of months that's a Jose Cuervo type. Finally just ordered the power amp from Peavey. Dead short in the DC section. Replaced all the transistors, caps, and resistors. It's a good thing I've got a day job to pay bills. My real question is: What type of signal generator are you using? Does it have square, sine and notch wave?
+professorhardknock Hello, good to meet you. Sounds like a fun project underway. My generator is simply an old Heathkit tube type sinewave. I discovered that the new audio generators out there generate noise as you sweep frequencies. So, I found it was best to fine a nice old analog model
Thank you for this.
Are the speakers connected as well ( in parallel ) as the scope?
+Peeka Boowi Hello, yes, that is the configuration
I like you comment about the red wine. I agree totally. One day I'll sent you some good South African Red Wine....
Hey Terry, do you have any videos on troubleshooting pots not working when it's not the pot itself that's faulty? On a fender handwired amp
You then need the schematic diagram and layout for your particular amp and some basic test equipment to have a prayer of figuring out what's wrong. Assuming you have basic grass roots knowledge of audio amps in the first place. Of course this is assuming you've done a thorough visual on all solder points, wires, inputs and output, and connective cables, etc.
My 1977 silver face has that same 2uf cap I never touched it.
I had a Bronco try to kick my butt one time. After fixing a Super Reverb, Carvin, and a Marshall, one of these little simpletons drove me crazy! I kept finding little problems, but the one that was causing the issue. It ended up being the ground to the chassis of the 6V6 cathode resistor. It looked good on a quick visual, but was loose. A reflow fixed it.
+rjake61 Good repair man. Yep, bad solder joints can be a challenge. I normally inspect everything with a lighted Luxo x5 magnifying lamp. Usually I can spot the troublemakers.
Very interesting
I noticed you have Amplitrex AT 1000; impressive stats. My brother brought down a knock off guitar amp (low power) solid state with one 12AX7 not even two years old. He complained it would intermittently cut out. I found the 1/4" jack was bad, but still useable, pulled the 12AX7 tube and tested it on my B&K 747; GM was questionable to poor on both sides. Unfortunately he would not leave it with me to complete my analyzes. I wanted to find out why the tube failed so quickly, needless to say the unit was poorly designed and constructed.
Hi, i really like your videos. thx a lot! 1 question: what resistor value did you installed to get the bias down to 34ma? the original was 520 ohm, but i couldnt see the value of the replacement resistor. thx....Stefan from Belgium.
Hello, I cannot remember the value. The amp was set up for a harp player, so he wanted reduced gain.
+D-lab Electronics np...i suppose it should be around 800 ohm...thx again....
I would like to know how to figure out the year on the champ
I have the same champ amp
Ab764 but no ser number
Schematic has I-FD on it
Don't know what that is
CBS musical instruments
Last numbers on output former is xxx-3-28
Thanks for the insight... and for sure.. you gotta have a celebration glass of wine.. I know I do )))
Hi Terry,
Enjoy your videos!....My Wife of 28 years hates my guitars and amps..and anything to do with my music!..But she will sit through your videos ..I think its the red wine you flash around! Checkout THE MEMPHIUS SUNS my Traditional original Rockabilly!...Question for you I just bought a mint 78 Fender Silverface Pro-Reverb...I have looked everywhere on the net for some help and there is NONE!...My master volume push pull Pot has a bad dead spot between 7 and 9!....I have been told I can replace with a standard 1 meg pot...But because this amp is in mint original condtion Id like to keep it push pull...I have found CTS make the right replacement but before I attempt... I was wondering if you may be able to do a step by step replacement Video of the MASTER VOLUME Pot in a Fender Silverface amplifier?... This is the part POT - CTS, 3/8" BUSHING, WITH DPST PUSH-PULL SWITCH - A1M...If you could do this some time would be much appreciated world wide.....Cheers Frank...Have a sip for me!
You are awesome! Too bad I have a Fender Acoustasonic (Non-tube) having intermittent hum issues. A tap on the amp sometimes makes it quiet. It has been a great acoustic amp. Any Ideas? Randy
Hello, The issue with your amp is cracked solder connections. Inspect the board with a good magnifying glass and bright light. Pay particular attention to power resistor/diode and potentiometer mounting connections, they get stressed easy
Nice, thanks. Even love the over emphasised Americanisms. 👍
What kind of mini tone generator is that? Looks like the size of your multimeter. I like that thing.
Thats a Tenma 72-505, hand held audio gen
Thank you! I enjoy your videos.