Red Plating Power Tubes Fix - 1966 Fender Blackface Bassman
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- čas přidán 23. 01. 2017
- In this video, we'll find out how to spot red plating 6L6GC output tubes in a modified 1966 Fender Blackface AA165 Bassman Head. This amp was purchased on Reverb.com and damaged in shipping, so this evaluation is for warranty purposes. We will determine if it's just a tube issue or something in the circuit. We will also see what sort of problems a microphonic preamp tube can cause. And we will generally explore the guts of a typical Blackface Bassman.
- Věda a technologie
Damn! At 16:48 when your finger went into the cage and got bit... I jumped. 2 seconds earlier we were looking at the 450+ VDC meter readout. Good thing your other hand was holding the camera and not touching that chassis.
Just found your channel. Dynamite stuff! I will be watching your videos all this week.
Wicked pissa!
I just recently found you. I've been liked all the videos I've watched, till now and thanks for that because, even when you do not explain in detail all the things, for a person like me that like and love this world of music and amps repairing, and who is still learning electronic, I'm learning a lot with you bro. Keep going. Greetings from Venezuela. Look!
At 10:14, that terminal strip there is not indicative of a mod "that someone changed their mind on", nor was it added after the factory. This is an AB165 Bassman, so that was a factory-installed part! It's the original terminal strip to allow for output tube balancing, as the left 220k resistor would extend off of the board to that terminal, and then over to the right lug of the bias pot. The earlier (AA864) design is the one that did not have that terminal strip added (same deal with the 220k's on the tag strip near the output tubes). In the case of this 1966 Bassman, the previous owner decided to revert to the AA864 layout by going for a true bias for the pair of 6L6 and also remove the 220k's on the other terminal strip.
those nickel parts are legit. that stuff stays surprising well. i have around 20 plus piggy backs well i did be fore my heroin addiction but most of them had really clean metal
Thank you so much, I am learning lots from U, thank you!
I had two of these... amazing little amp...
Always a great video, but I was hoping to see that it wasn't the tube... I can remember going to the pharmacy and testing all of our TV and Radio Tubes and I even tested the new ones and the guy would always say they're brand new, even though I found a few bad ones. Either some hanky panky or were banged around in shipping... I was like 7 or 8 and I had enough sense to turn the TV or Radio off and unplug it and turn the power switch on before tinkering. Just a memory.
That takes me back to my teen years when I worked with vacuum tubes.
They haven’t changed
Thanks for the vid!
An impedance mismatch on the output can also cause a tube to redplate. I've run into a number of older marshalls that would redplate if running through an attenuators. In these cases, the redplating comes and goes as you are playing-- in other words, at idle it's fine, but as you play and a note is ringing out, the tube will start to glow. One solution is to bias it a bit cooler (or avoid using an attenuator?). Rule of thumb is bias to about 70% of the max dissipation of the tube spec, which I've found to be fine when dealing with amps that are not being pushed hard, for clean tone, or preamp distortion (and using good quality NOS tubes). However if the amp is being pushed hard to get output distortion and/or using new production tubes, I've often biased closer to 50% diss. I know that may sound like it would run cold, however, keeping in mind these amps were designed to run on 115vac yet now see 125vac or more, they simply are running hotter. Bias current is basically setting the dissipation at idle, however when overdriving the output, you are now going out of spec compared to what is on the schematics, so at that point you could be essentially exceeding the max dissipation of the output tubes. Another "quirk" with the long tail phase inverter like used in Marshalls and fenders, this type of redplating doesn't follow the tube, but stays with one of the sockets and is "normal" behavior when pushed (again, while running clean, it's fine, but overdriving the output, now things are out of spec). Changing the tail resistor value can help "balance" the phase inverter and mitigate the issue.
As finicky and quirky these old tube amps can be, nothing beats the tone, feel and overall experience playing one of these classics!
Oh it was mostly all on purpose and seeing the limits of whatever particulars, where do you live that the wall is still that low? wow...The plates can mostly handle the crazyness and far above what was rated it's the screens and could rig up even more resistors and try to dissipate that current cause that won't fly well being high anything.
I also think the voltage at the plates should be reduced, 457V is a bit high.
awesome!!, this was very informative! thank you! :D
great stuff ,very interesting
I had a KT-66 tube in a push pull pair in a Heathkit W-5M amplifier that would develop grid leakage after about 10 minutes, one tube would just run away into full conduction. It took out the output transformer, but fortunately i had a parts amplifier as a donor.
Tube tester would not find the bad tube. I found the problem after replacing the output transformer and monitoring the cathode voltage null. (bass balance) New set of reproduction Genalex Gold Lions solved the problem.
Those tubes aka 6L6 TAD tend to do this intermittently especially in my more modern Fender amps. Aka Champ 12. I had one reasonably new all of a sudden fizzle, turn red plate, hen dark blue, then smoked itself in a Cathode single ended class A amp.
Dear Brad,
Thank you for explaining what red plating is as well as having a visual example.
Once upon a time, at a show, my Marshall JCM2K had a sudden loss of power and grit. During a break, I looked at the back of the amp and one of the EL34s was dark. What may be interesting to note is I opened a window near my rig hoping that would help keep things cooler (summer night show) so the amp would be happy.
Anyway, once I got the amp home and removed the back cover, the tube looked normal EXCEPT the glass in the mid-section on one side had melted inward to a small black hole... like a spent smoke bomb. A google image search for melted EL34 shows I'm not alone.
I presume my melted EL34 is the final destination when a tube red plates, no?
Thank you.
Yes. Eventually, the tube will self-destruct in the manner you mentioned, or it will take out other components in the amp and cause a smoke and light show.
Luckily I hit the tube lottery when I had to replace my 6L6's in my Peavey and my EL34's in my Marshall, both amps have been powerhouses for a few years with no issues. Sometimes you don't hit that lottery, and that's always a bummer.
I have a Bassman Ten. It had the SS rectifier like this model, but unlike this Bassman, the transformer had an extra secondary (yellow) that I used to install a GZ34. Blasphemous maybe, but I made the change and never looked back.
I enjoy your channel Brad. As far as shipping goes I sent a 1936 Northern Electric (family unit) tombstone radio from Toronto to Orlando, to a family member. Double boxed and bubble pack wrap. "Handle with care antique radio". It arrived crack in case and the 80 rec tube came out of the socket. Purolator to UPS at border. They will not take insurance. Just spent $500 bucks to update and service. So little glue to fix the crack in the wood case and put 80 rec fac and check It works . There shipping companies are lame. I think the issue was the handle with care antique radio is a message to the mental midgets to kick the shit out of it..
The aa/ab165 is the greatest circuit Leo ever made. It can make a wet fart sound beautiful. Funny how all the best bass amps make even better guitar amps
Hi Brad, love it when you talk about how and why components are installed in amplifiers.. Nice amp. I lust read something about 'flyback' voltages... A lot of people think it is okay to use a 8ohm speaker if you have a 4ohm output transformer, or a 16ohm speaker with an 8ohm tap. However, the flyback voltages going back to the tubes when the speaker is returning to 'neutral' can be quite high, damaging the output tube sockets or tubes.. As always a great video and good tech tips... Take care, Tom
While running a bassman with an 8 ohm cab probably won't hurt the amp or the cab in any way (given proper wattage rating), it will create some flyback possibly. Since probably 80% of the guitar cabs out there are 8 or 16 ohms, the diode mod from the plate to cathode is probably designed to prevent a possible disaster scenario where maybe someone tries to plug into a 16ohm Marshall cab and crank to 11.
The flyback diodes are intended to prevent flashover in the output tubes, or in the OPT primary, which can cause shorted turns (and a ruined OPT!) In addition to a speaker impedance mismatch, plugging in a guitar with the volume at full or pulling out the speaker cable when the amp is working hard can result in flashover.
one sharp tech!
Hey Brad question, have you tried the newer Tung-Sol 7581a tubes? Was thinking of getting a quad for my PRS Archon 100 and wanted to hear your thoughts, thanks.
Btw looking for a good quad of power tubes with good nice top end, not to bassy. Thanks
The 2-lug terminal strips are original, but the main and bias eyelet boards are absolutely brand new. The fiberboards are way too pristine, and aren't rippled the way 50-year old fiberboard do as they settle/age. The boards *could* have been replaced due to absorbed humidity causing leakage, arcing or static noises, as this is a common problem in Fender by this age. Fiberboard replacement is often the only sure cure.
Most of the carbon comp resistors on the board are Xicons. You can tell by the particular color scheme, and which color bands are hard to read against the background. Additionally, the Xicons are all 5% tolerance, and there were only a couple places Fender ever paid for 5% tolerance. The couple of 10% carbon comps are a different (probably older) brand.
Sadly, the blue molded caps and ceramics are probably original parts someone had stashed away to build up this board.
Pots & wiring from pots-to-board looks original. However all the yellow wire from the new main board to the tube sockets is new stuff.
It's not clear (by 10:00 in the video) if the Deep switch is even hooked up anymore (later is looks like the Deep switch was converted to be a tone stack defeat). The black stamps on the chassis above/below the punched serial number on the back are probably dates of warranty service.
Filter cap board is new, along with new filter caps, new wire & new resistors.
All-in-all, this looks like someone took an original '66 Bassman and opted for a complete rebuild, minus pots & transformers. Probably not a bad things when you could buy those all day for $400. Now people may be more sensitive about collector value for this amp.
That's an original board with original yellow cloth covered Celanese wire! The yellow "E" on the board is original. I see amps like this across my bench all the time, and some look really pristine. Plus, you can take isopropyl alcohol and a swab to clean solder rosin spatters so well that you would think it was a new board (this is what I do in my restorations). The other tell-tale signs: you can see the solder joints on this board are vintage style and original looking, especially where carbon comp resistor eyelets were not messed with by the tech. Compare the eyelets where the tech replaced parts to the eyelets that weren't touched (which don't have rosin surrounding the eyelet) - the tech used a solder, temperature, and technique which deposited excess rosin around the eyelet. A good spot in the video for this is at 14:10.
Just out of curiosity, what brands of tubes do you like better then others... I really have a very hard time figuring out brand specs these days.. but with a house full of Hiwatts, Marshalls, and Fenders, I am always trying to figure out brands to "go to" before others...AND, have you done a vid on PROPER three prong plug wiring? I am currently working on a Kalamazoo amp, that will need, among a few other things, a PROPER three prong plug installed. ANNND.. can you go into more detail on the "death cap"?
Man replace the filter caps you've got nearly 3V AC of ripple on main 450VDC supply rail?
A Weber Bias Rite would make your life a lot easier :-) Or put 1 Ohm cathode resistors in.
Can you discuss the possible mods to that post next to the Bias Pot? I just opened up what I believe to be an AB165 but it seems that the connection between that post and the bias pot have been disconnected. Any idea why that might be?
I have a Marshall JTM30 2x10. That model has been known to have heat issues. I don't know what happened to mine, but one day it would HOWL a low pitch and grinding noise like a jackhammer. It sounds like gears grinding together and leaf blower at the same time. What's your best guess?
Was there any follow up on the fix (?) ...and possibly the power tubes should be proper 6L6GC as I believe the 'W' denotes a tube with lower specs (?)
...but I'm just learning meself.
Thanx for another great vid and...
cheers
W means industrial rating.
Brad, I have a Pignose GR60 combo and it red plates and blows my 6L6s. The tubes spark internally and stop working. This happens as soon as you power up the amp. What should I look for as the problem. I know you mentioned some reasons why this happens and I will certainly check all voltages but I need somewhere to start the troubleshooting. I had a Bassman just like this one. Used for bass and loved it. Thankz
I would personally fire it up on low input voltage on a variac and test the voltages on the grids. If you have any significant positive DC voltage on the grids, you have bad coupling caps. Next, try removing the power tubes and fire it up slowly and test voltages at every point along the power supply. Check voltages on both sides of the OT, etc. That's probably how I'd start. I sure wouldn't just drop brand new tubes in and risk frying new tubes.
The Guitologist You are so right! I will not put the new tubes in before I troubleshoot the voltages. I guess I was asking for a simple reason, but I should have thought about it cause what you said made perfect sense. The iron and caps in this amp are cheap Chinese crap and I am lucky I got as much use out of it as I did. I think I might just rebuild it with USA iron good quality caps and resistors cause it is a gigging amp, small, loud, with good tone, so thanks. I wish I had kept my Bassman! O well, I will just build me one. Thankz
Not that it's a big deal, but those chassis straps and screws could easily be original. Going by how clean the cab is, the faceplate, and the chassis inside and out, I'd bet they are for real. Not every amp was gigged a lot or exposed to moisture. But yes, some straps get rusty and dented, and hacks will bugger up those Phillips heads.
You'll never saw any filament glow on a regular 6L6GC on the top of the tube, except on the bottom near the socket. Those tubes are 5881s that's why you can see them glowing on the top.
i notice your tendency to want to remove the ground switch just because the amp has a 3 prong plug. If you gig in bars that are in old buildings, you often have to use a 3 prong to 2 prong adapter. I believe having the ground switch may still be functional in these situations.
I watched a video on a Radio station in cincinatti from the 30s that was the first in America to go past 100,000 watts and ended up ramping up to 500,000 in the end. And they had an array of Tubes that were water cooled with distilled water through pyrex glass pipes and had an outer glass water jacket on each of them, and they had a heat exchanger somewhere in the building with a cooling pond outside for the standard town water. And they had a rectifier that was in a Giant sealed Vat filled with 60 gallons of oil. They had to actually install supression antennas next to the main ones because they were garbling a radio station in Canada, I assume broadcasting the same thing, just out of phase. They had to dial it back to under 10,000 watts at night as that was a rule for every radio station (and I think it still is today) because of a rule of interfering with European radio transmissions. Apparently during the day, the wire fences on the houses next to the station would rattle with the bass notes of the music. You can go and tour the Station today, if they could broadcast modern music through that station, it would sound so crisp being all tube, especially if it were played off vinyl.
shoominati23 the station was WLW belonged to Powell Crossley.Of radio refrigerator and crossley automobile fame.Although non functional,the station still exists and the do tours.
you do realise the pot is for balance and only varies one tube, don't you?
What? didnt say nothing about pot aspect dude
shoominati23 sorry,I was reading your post and replied about the great WLW station and then wanted to tell Guitarist,the guy in this video fixing this amp that I know them well and there's a bit of an odd setup in the adjustment.Sorry, wasn't meant for you.
Mr3906ce, The CBS Fenders did that to the bias circuit and some of them had a screw pot on the rear panel labeled "hum balance". The thing to do is to rewire these supplies to the old blackface specs. You end up adjusting a single bias voltage that's fed to both output tubes simultaneously. The wonky hum balance "biasing" might help somewhat, if the output tubes are mismatched, but a well-matched pair should get about the same bias voltage as one another.
It looks like the cabinet was from 1966, but the chassis is from 1967, if I am looking at things right. The chassis also looks like it was converted from the tube "balance" adjustment to a bias adjustment.
I'm really enjoying your videos, thanks for doing this! I have a Crate BV60H, which from what I've figured out and read, is a bright voiced amp. I'm looking to bring down some those higher frequencies making the tone too harsh, fizzy and somewhat muddy. My EQ is set just about neutral and I don't use a ton of preamp gain - only at about 10 o'clock at most. I clean and low gain boost the signal from my Seymour Duncan JB/59 loaded guitar with a Boss SD-1, pedal and guitar tone knobs set to 50%...roughly neutral. I had it retubed in early 2004 with EHX 12AX7 and 6L6GC tubes. The tubes haven't been subjected to high output very much and aside from some recording in the 1st half of 2004, has only been used at reasonable household volume. I've been thinking of switching out the preamp EHX tubes for JJ ECC83s, but wanted to get a good opinion from somebody reliable.
i know im asking the wrong place but does anybody know a way to get back into an instagram account??
I somehow lost my login password. I would appreciate any tips you can offer me.
@Emanuel Creed Instablaster :)
@Curtis Marcus i really appreciate your reply. I found the site on google and I'm trying it out atm.
Seems to take quite some time so I will reply here later with my results.
@Curtis Marcus it worked and I actually got access to my account again. Im so happy!
Thanks so much you really help me out!
@Emanuel Creed no problem :)
Hi Brad, I own a 1966 fender showman head that has the tubes red plating after turning it on for about a minute. what would be the first thing to look at? the amp is all stock except for the tubes.
Take out the output tubes, and with the amp switched on, look for around -50V on pin 5 of the tube sockets. If it's not there, it's problem with the bias supply. If there's a negative voltage, but it's lower than -50V, then your amp is biased too hot and needs its bias adjusting.
Those tag-boards are original. The little one by the bias-pot was holding extra resistors for the original "bias-blend" design. Someone modified it to a classic bias-design AA864-ish. The larger one by the 6L6's used to hold a pair of 220K resistors from the eyelet board (1 going to each tube), also part of the bias reconfig.
Could you please tell me how exactly do you clean the pots? The volume knob on my Stratocaster recently started crackling and even cutting off completely at one point of its course and i don't know how to fix that. Thank you!
Thanks a lot for that! The problem is i actually live somewhere in Asia where it's almost impossible to get good quality parts or electronic of any kind, bit of a Robinson Crusoe situation i'm afraid. So i have to make do with what i brought with me and as i only took one guitar here having it go down would be a major inconvenience. I recently took it apart because of a very loud buzzing, a pickup that didn't respond and some kind of weird harmonics (in fact i did tighten the jack socket a bit too) and it's when i put it back together that i noticed the problem, the tone pot was very hard to turn but worked alright, the volume pot though made some pretty bad crackling noises. I'll try the WD40 tomorrow and tell you how it turns out. For info my guitar is a Fender Stratocaster HSS MIJ Squier Series, only two pots, a 5-way switch and a Floyd Rose II.
You have two distinct types of electronics cleaners: Those that leave a residue and those that don't. For pots, always use one that leaves a residue, this is specifically for lubricating the pots. With no residue, the pot can and does seize up & won't rotate & then we are screwed. On the rear can of most pots, there will be some small openings, and that's where you'll spray a good amount of cleaner into the pot. Do that, and then rotate the knob back & forth fully, about 10 or 20 times. This is the accepted method of cleaning noisy pots. If doing this doesn't take care of scratchiness, then you need a new pot. An exception to this rule is for the presence control on a lot of older Marshalls & some other amps. These pots have a DC voltage on them, and no amount of cleaning or replacing will cure the noisy operation. Keep some paper towels handy and clean up any spills immediately. The residue will gather dust over time, and then it becomes semi-conductive, so you don't want a film of cleaner residue on the board or components or anywhere else but inside the pots. That's where using the non-residue cleaners comes in. For your guitar's switch contacts & output jack, use a non-residue cleaner. A good thing to look for would be a set of both, like Deoxit & Deoxid. One leaves a residue, the other doesn't. Zed1967's advice & tips are spot-on, too.
Question Brad: what's the percentage of customers who refuse to pay? And how long can you hold a persons amp before it becomes your property? Is that determined by State or local laws? Thanks. I just repaired a Heathkit C-1 capacitor checker for a guy who has now put off paying me for going on 30 days, just wondering when I can resell it to recoup my cost in it.
Did he ever come back for it?
These are OT protection diodes, in case of a shorted tube.
That amp was in good shape, and sexy looking. Yes, I suppose I'm a ampgeek.
If you think that amp is sexy you have a sexual identity problem and or a very small penis to fit in the input hole.
Please use correct adjective for the situation. Amps are not SEXY!
If you don't have a matched pair of output tubes, and you adjust the bias, even though the bias is 'right' for the pair, could one tube redplate because of the mismatch?
Not very likely. I won't say it can't happen, but even tubes from different manufacturers, if they are in good working order, should work in a mismatched PP configuration if they are within operating specs individually.
Is it safe to hot-swap preamp tubes? Is it safe to do it with two hands (i.e. breaking hand in pocket rule)? just wondering for my own noobish safety.
Sonamor, the short answer is, "yes". You should be able to pull any or all of the tubes from a live, energized amp. You may make some loud noises when doing so, but nothing of the amp should be harmed.
Putting the diodes in series is probably to increase the reverse breakdown voltage of the protection circuit.
Im thinking your stamped date codes are first two digits week and second two digits are year... 0266 would be second week of 1966
Sum total of the diagnosis? Read planning follows the tube just like the customer said so recommend changing tube.
1966 Fender Bassman
I always wondered who thought it was a good idea to have the valves pointing downwards. All the heat goes to the base of the valve and it's sockets and associated components. It must shorten the life of such components.
The plastic bases hold up ok and as long as the sockets aren't direct board mounted, they're usually ok, but increased heat inside a chassis probably does "bake" components over time (particularly stuff like screen resistors and grid stoppers on the sockets.
Hi Brad,
As far as AA165 vs. AB 165 circuitry goes it should only mean the transition when Leo Fender sold out to CBS.
AA = Leo...AB= CBS.
Whatever CBS did after the buyout is who knows?
I'm sure CBS used all available components that were still in stock until they ran out and just printed new pieces of paper to stick inside the cabinet.
I assume the different codes mean a different circuit revision, probably roughly also corresponds to the Leo/CBS change also. Thanks.
Who knows what CBS did in the circuitry after they bought out Leo.
I was only 16 when it happened and wasn't there to tell them "don't screw with things". lol
The AA165 merges the normal channel after the 2nd preamp tube. If you channel-jumper one of those the sound is out-of-phase and horrible. An AB165 merges before the 2nd tube and mixes an even # of inverting gain-stages. Mine jumper'd well and sounded great combined. Do not trust the paper labels; most were wrong. Mine said AA165, but was really an AB165
Thanks for the info. In the transition era it was who the hell knows what's going to happen.
its rare to get a used older amp and the tubes aren't worn in them. no one replaces their tubes before selling an amp and if they do, usually switch them out…tubes aren't like tires on a car.
Will touching a tube with bare hands ruin it? What's your opinion? Im sure everybody has heard this opinion regarding oil from your hands...
This red plate issue happens when capacitors from inverter stage leak trough power grid tubes.replace old capacitors
What type of license does someone get to become a legal and legitimate Electronic Tech? Is there a state Exam?
Diagnosis starts at about 15 minutes in. Long sightseeing tour before
It wasn’t H8, it was HB0065. That number is just a model number. You have to have those labels for the factory assembly.
Those top pieces and that handle are absolutely original. My '74 parts look brand new. Why would the bolts look like anyone had turned them? It's not something that needs to be done more than a few times in an amp's life. Give me a break.
Those terminal strips are not mods. By 66 the bassman already had weird CBS mods. Those are factory. It's from part of the bias circuit and a local feedback loop that is removed.
Hallo Brad,howd I miss this one?Age I guess.
Couple of things. Run the input voltage from the mains at 115V if you are going to compare your voltages to the schematic.
You can disconnect the standby and death cap but if they are securely attached leave them in the amp. Doesnt hurt and some owner will eventually lose them. These amps will probably outlive many of their owners.
By that point in time Fender was getting a little sloppy. Make sure that the filament wire that goes to 4 and 9 on each preamp tube always goes to 4 and 9. Sometimes they would , especially on V1 get the 4 and 9 backwards.
Hard to see in the video but it looks like the guy already did it. Fender used to fuse the neutral. That works but it is recommended to fuse the hot.
They are solid amps, sound good and are kinda fun to work on. Enjoy!!
"By that point in time Fender was getting a little sloppy."
That problem came a little later in '68-'69. You'll know by the whitish PVC wiring (if you could tell by the wiring slop).
"Make sure that the filament wire that goes to 4 and 9 on each preamp tube always goes to 4 and 9. Sometimes they would , especially on V1 get the 4 and 9 backwards."
This is a non-issue and a Gerald Weber myth.
Always remove the tubes when you ship an amplifier! I will never understand why folks think it's a good idea to leave the tubes in the sockets when they ship an amp.
I can see this both ways. I have received amps and shipped them both ways. I think if the tubes have shields in place and if the sockets are tight on the power tubes, those can sometimes be shipped with the tubes left in place as long as they are packed well with packing material all around them. It's kinda like stuffing a turkey...you have to stuff the inside of amps with bubble wrap or whatever so that the material surrounds all components and keeps everything from moving. I have opened tubes packed separately and had them drop out of my hands and break on the floor. Either way you go, there are pros and cons. I've also had people put tubes back in wrong that I've shipped to them.
Then why when you order amps the manufacturer ships them with tubes? I know Marshall and Bugera ship amps with tubes.
That is exactly what I was going to say
My marshall, blackstar, egnater and three oranges all shipped with tubes installed :)
The manufacturer ships their new amps with the tubes installed.
Redplating to me is a runaway current on the plates !
Too hot a bias or bad tube usually is the problem ive found !
Can also be leaky coupling caps that are usually between the phase inverter and grid of power tubes. When these leak DC which is being supplied to the PI, it increases the positive DC voltage on the grid, causing bias to begin going crazy. Tube meltdown.
way to not use the standby switch when swapping the pre tubes.
#persnicketty
That was a 3 amp fuse yes but it was a fast blow... which is totally fine to use in place of a 2 amp slow blow
The one tube is glowing blue, generally indicating a leaking/gassy tube. It will often cause excessive plate current in the other tube, which then is eventually glowing red. A quick test on a decent tube tester would also have revealed this, as well as a likely imbalance between the two tubes. On an amplifier with a balance adjustment for the tubes, these two tubes may still be good to use.
Maybe it is the red plating tube or sometimes it is the other........... a little weak.
you do realise the bias pot only varies one tube, It's a balance control for the plate current of the two tubes.Its not for changing the bias to both tubes.
Mr39036ce : This is The Guitologist's channel, and not mine. Having said that, you are not helping Brad or the viewers. If you would rewatch the video you can clearly see the 10K bias pot is wired for bias adjustment and not bias balance. Just watch where Brad is adjusting the bias voltage, at 18:50.
This is a generalisation. In some circuits the balance pot actually affects both sides of your push-pull arrangement. So turning the pot one way increases bias on one tube and decreases it on the other.
I've got a video coming for a 1975 Bassman 50, and it'll show me my measurements on both 6L6 output tubes affected by the bus balance pot.
A glance at the schematic of the stock AA165 shows a bias adjustment pot, not a bias balance pot.
i believe the bias pot controls the overall current period, The balance does just that to even out differences in overall current between the 2 tubes. The balance pot is usually mounted on the rear panel. Balance came out well after CBS bought the company and isnt a stock feature on BF fenders.
@@kenb.1829 sorry,got the reply wrong but know the bias on these by heart.the control does vary bias but on 1 tube only.Check the schematic yourself.Thus was a design as being a bass amp and assuming increased bass control settings,the best result would be attained by being able to balance out any output stage hum components.I don't believe this was used on any other Fender amp.
24:29 red plating
"STR" special tube request. Peavey's Fenders, Mesa Boogies.Tung Sol Russian?
Yep, the STR's would have heavy-duty filaments, extra vacuum, and double getters. The idea was to design a rugged tube specifically for hanging upside-down in a chassis & withstanding higher temps & vibrations
Hey Brad, at least your honest! I don't want to be rude because your learning, but I have over 50 years exp. on you. STR Sovtek Russia, and the issue is heater to cathode short 9 out of ten times but not always. Also VT1 is almost always a problem. There has never been an amp of any make or model that i could not fix correctly the first time. Yes I am a GEEK and an OLD one! Before you make a video, please do your homework because there is no substitute for exp. Sorry for being so kurt, but I have shoes older than you. LoL Know your stuff because you don't want to mislead your good followers. Cheers
so.. you pull it apart, see some diode hanky panky @ the power tubes, note that it is abnormal, but dont investigate the net result?... ok. then roll a few preamp tubes for noise isolation. do all you can do to convince the plate glow was fake news but stumble on to not... swap tubes to isolate, which your client already knew & translated. you dont isolate neg voltage or current draw for each tube... and done?.. what useful info were you able to provide your client?.. he already knows what you proved in the video?.. he's gonna buy matched new tubes & ruin them too, lol... you def do things different than i would.
reverb is definatley a no go for me. the honest sellers get the shaft while the crooked ones selling problematic gear don't. I for one will NEVER buy or sell on reveb, they can go pound sand. I use and will continue to use ebay which with all the problems that come with it and paypal it is a million times better than the corrupt organization that is reverb.
Kinda disappointing. All i witnessed was 27 minutes of video to varify complaint... no fix at all.
way to not use the standby switch when swapping the pre tubes.