Caps and a Blackface AB763 Bandmaster

[JoeM]

Then I would consider nearly 50 year old caps like bald tires. Get the caps replaced by a qualified tech and you'll have an amp you can depend on.

[Modorange]

OK Thanks for the analogy.

Chuck, here's an analogy.. Let's say you've owned 20 or 30 old classic cars, and there's a guy who was working on them since when they were produced in the 50s, and so then he tells you your tires will need to be replaced but they are still good right now. This is a trusted individual who has saved you literally hundreds, perhaps thousands of dollars through his work and knowledge of cars, and he's "lived and breathed" cars.

Then, you decide to get other opinions on the tires, because they are indeed older. You post it on an auto mechanics' forum and somebody tells you to find another mechanic. You don't know that person from squat, but nevertheless he tells you to "don't tell him, just find another mechanic." What would you do? Would you listen to this guy who's out in the internet ether? There is value in personal experience and there is value in hearing opinions. I have a priority list. I'm willing to admit if I'm wrong, and I'm willing to live with the amp if caps do indeed blow up and bleed caustic chemicals all over the amp, etc. if it means that I've had a valuable learning experience, it would teach me well. On the other hand, as I've already stated several times, my mechanic has said the tires need to be replaced, so he's saying the same thing. Maybe he just doesn't see the amp the same way the internet people do, even with this high-res photo of it. I don't need to speak for his expertise, it is based on years of his fixing my and many, many other people's items since before most of us was born. I'm just not getting this "find another tech" thing and "don't tell him." There's an analogy as well. So I have heard these opinions and I appreciate it. Thanks

[Chuck H]

Cool. In your position I would probably feel the same way.

We here have seen the rough abuse that some guitar amps are put through. Our advice is intended to be fail proof for this reason.

You mentioned my phrase "just don't tell him" a few times. I was being glib. Also, by your same above analogy, there was no way for me to know that your tech isn't another 'Smokin' Pete'.

Enjoy your amp.

Chuck

[JoeM]

I dont see a 3 prong cord on this amp. Regardless of what you decide to do on the caps, this is a safety issue, and if it still has the original 2 prong cord, get it replaced with a proper grounded AC cord. There's other threads on this here, do a search for "death cap".

[soundmasterg]

We are all speaking from experience here. Many of us are performing musicians who need to rely on their amps to work and work well without risk of failure. I would not want to rely on a 50 year old car with 50 year old tires, even if they appeared to have good tread. The rubber gets hard and the tires will crack. That is the same analogy as the electrolytic caps. The electrolyte in the caps dries out and the cap cannot do it's function anymore very well, even though it sounds ok right now and the caps haven't leaked yet. Eventually if you let it go long enough, then the cap fails, either by physically leaking electrolyte or by failing to decouple the AC to ground, which can cause tubes, and then transformers to fail. Sometimes there is a warning effect where you hear increased hum or other noises, but more often there is no warning. One minute you are playing your amp and everything sounds fine, and the next you see smoke rising from your amp, and if you don't catch it soon enough, the tubes cook themselves and your transformers arc internally, and boom, you've just ruined a valuable vintage amp. If you just play at home every once in awhile, then the performance need isn't there, but the risk still is, and in some ways, more so, since electrolytic caps do better when the amp is played on a regular basis. I am into vintage cars myself, and one thing I never compromise on is safety, and that goes for amps I work on and own too. If it was mine, or a customer brought it to me, I would replace the electrolytic caps in the amp, change to a 3 wire cord and disconnect the death cap, replace any coupling caps that are leaking DC past a certain amount (requires checking each one), replace any plate resistors drifted out of their tolerance (requires checking each one), and replace the dropping resistors with metal film ones for safety reasons. Carbon comp resistors tend to burst into flames in failure, and in the power supply there is no reason to not use metal films since the sound affect does not matter there. For the plate resistors I would use new carbon comps if necessary to replace. At the very least however, I would change to a 3 wire cord, get rid of the death cap, and replace every electrolytic in the amp. If it doesn't absolutely need to be done now for the amp to function, it will within the next 5 years, guaranteed, and when they fail if you don't replace them until they do, then you might destroy your amp. Its yours to do what you want with, but you asked for opinions and there is mine.

Greg

Greg

[Chuck H]

OK Modorange... Here's something to chew on... Maybe your not inclined to take an internet opinion over the word of your trusted tech who's been servicing your amp (since it was built it seems) (also being glib, don't pop a vein). But how about considering that many of the posters here, in fact many on this very thread, are also respected amp techs, not goof ball hi fiers with some half baked lore for an ideology like many other sites, that stand to gain nothing by whatever decision you make and yet all are freely giving advice that you want to oppose for the word of one man.

I dunno, it's your call brother. Probably the worst that will happen is that a cap will leak and there will be some clean up and parts replacement needed. But at it's worst this kind of neglect can end very badly. What kind of sage advice then is it to take that risk when the preventative costs are so negligable. Would you drop your childs medical insurance to save $$$ just because he/she didn't really need a doctor much last year?

Chuck

[pdf64]

When folks make analogies between cars and amps, things get confused quickly, especially when safety is mentioned.
1. The amp must not be used until a properly grounded power cable is fitted. Currently, the only barrier between the amp chassis (and therefore the player's guitar strings) and line power is vintage laquer (on the primary winding), and paper former. A grounded chassis would protect the player from line power if the winding insulation failed.
2. That's the only 'safety' issue that amp has. If the caps explode, it is very unlikely that they will harm the user - maybe the tech if they go whilst on the bench, but he's got the opportunity to assess prior to powering up, and to take mitigation.
3. It would be beneficial (for tone, power output, and reliability) if the amp's consumables (eg electrolytics and CC resistors) were replaced. So many will be age / use degraded that it isn't worth (IMO) attempting to identify the ones that are in-spec and serviceable. A campaign change out is justified. That was the query in the OP. It's up to the owner to decide whether they want a museum piece that limps along, or a reliable amp that operates as the designer intended.

[Kazooman]

I'll add my two cent's worth to the above. I have a blond/oxblood Bandmaster (6G7-A chassis 1x12 with tone ring) that I have owned since the 60's. Restoring it to reliable working condition was the best thing I ever did for this amp and I had a lot of fun and learned a ton in the process. I was comfortable doing the work myself, with the aid of some books and Internet research. You should take your amp to a good guitar amp tech, not a former radio/TV guy. Get the three pronged cord installed, replace the filter and coupling caps and anything else that looks suspicious. When you replaced the power tubes did you (or the TV guy) check the bias?

Here are a few images of the results. For those who might notice, I did leave the "death cap" attached to the chassis. It is no longer in the circuit. I just left it inside (the wire is now capped off for safety) for sentimental reasons. It reminds me of all the minor shocks I got off this amp before installing the proper cord.

Before:



After:



Before:



After:

[Modorange]

Thanks Chuck (I'll remain calm, you do the same), PDF, and Kazoo for the input. I will indeed change the caps when the opportunity arises or it is deemed necessary for reliability and tone sake (if the amp needs to be gig-worthy). I may try it myself or enlist Joe's assistance. I know you guys don't have any trust in him at all, and that's ok, the words are totally an incomplete picture and your assessment is based on that. I suppose I don't need to run anything by you and you can go on doing whatever it is you do without my opinions or comments. You're probably nowhere near us anyway. So in the end I make the decision. Thanks for the input.

[Wombaticus]

I sense I'm beating a dead horse here, but respectfully, it is already a reliability issue. Any tech that sees visible bulging on a half-century old electrolytic cap and doesn't recommend immediate replacement is giving advice that borders on the highly irresponsible. The same goes with the two-to-three prong plug conversion. Many responsible techs will not even agree to work on an amp unless the owner agrees that a three prong plug be fitted. You, of course, are at liberty to do as you please, but I must reinforce the notion that you are not receiving advice here from some bunch of internet loons. The folks here have far above-average knowledge of tube amps. Some are highly experienced techs, some are electrical engineers, others are actual amp designers and/or directly involved in the business of amp manufacturing.

Moreover, the reason we are concerned is that this is a pattern many of us have seen over and over again. Personally, when I think back to some of the fantastically poor advice I recieved from supposed amp gurus back when I was still just a guitar player and not yet versed in electronics and building my own amps, it makes me shudder. "Smoking Petes" are everywhere. Just the other day, I had a conversation with one of the major amp repair guys in my own town that had me coming away shaking my head. Ten minutes of talking shop was all it took to determine that this guy didn't really know how a lot of this stuff actually works.

Now, I'm not saying that your guy is necessarily bad -- but I will say that the rest of us are all seeing, based on our experience, what seems to be some red flags.


Anyway, good quality PSU caps are about $5 each or less. Read up on how to safely discharge caps and work safely on an amp. Then bust out the soldering iron and drop them in yourself. It's a half-hour job, tops. There's just no good reason not to do it.

[Kazooman]

Anyway, good quality PSU caps are about $5 each or less. Read up on how to safely discharge caps and work safely on an amp. Then bust out the soldering iron and drop them in yourself. It's a half-hour job, tops. There's just no good reason not to do it.

That was the reason I posted the pics. Not to try to impress anyone with my soldering skills, but to show just how simple this repair can be. There are other threads on the forum that give pretty detailed information on the three pronged cord replacement.

[Chuck H]

Many responsible techs will not even agree to work on an amp unless the owner agrees that a three prong plug be fitted.

I just want to back this now since I haven't yet on this thread. A guitar amp is not like a toaster or a stereo in that anytime it is on YOU ARE TOUCHING THE CHASSIS THE WHOLE TIME via your guitar strings. Most players have been shocked using a two prong cord amp, often due to inventive club stage AC wiring. A three prong cord is of no detriment to the value of your amplifier if you save the original cord. If your a player and not just a collector you "should" install a three prong cord for safety reasons. But it's your call.

As a side note my amps use a fifteen foot (three prong) cord. Very handy if your on a big stage and don't have an extension cord. Something to consider if you make the change.

Chuck

[pdf64]

Just to re-inforce Chuck (and all)'s point above, repeat my point 1, the amp must not be used until a properly grounded power cable is fitted.
It's not just about you/your personal choice and safety.
It may affect anyone you might lend the amp to, maybe just for 1 song at a jam.
It may also affects anyone who might try to pull your dying body away - they might get fatally shocked also - a friend, family member, or just a 'good samaritan'.
Now you know, you can't claim ignorance, you have a personal, moral and legal obligation to take the amp out of use (eg cut the line cord off at the amp).
Do as you see fit with the caps, but no right thinking person can ignore the above issue.

[Modorange]

I guess Leo Fender just had it out for all those players. It is my call. Hmm.. I hear all the predominant wisdom but when my son powered the amp up, and tells me it sounds great, and there's no need to do anything to it. I have the forum here telling me to replace all the caps and power cord, etc.. on one hand; and on the other hand, I have this fantastic-sounding amp in the band room and my son telling me to leave it alone. Anyway.. Feel free to climb on the dog-pile..

[pdf64]

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