Issues with one of my blackface bandmaster heads NEED HELP

[panoramic]

So i had a gig the other day in DC outdoors it was HOT out (like 90 +) and my amp was in the sun prior to trying to use it. (Prior to the gig we practiced for like an hour and it worked FINE there were no smells or anything really, i haven't had it serviced in the 8 years i've owned it) When i turned it on all i got was some low volume blubbery nonsense out of it and I had to use someone else's amp at the show. I tried to swap out all of the tubes and it made no difference, still low volume and flubbery
When i say low volume I mean like barely 1 level when the amp is at 10 and the notes are distorted and farty

any input appreciated. I just want to know what i am looking at before i take it in for a service

[somanytoys]

I'm no expert by any means, but that sounds to me like something in the power stage. Would a transformer do something like that and still work? If you swapped out the tubes, that only seems to leave something else in the line - plate, transformer, capacitors or whatever.

It could be that the pre-amp is the problem and isn't giving the power stage enough to work with, but it seems like it would still get something a little louder as you turn the volume up from the available preamp signal level.

One way I would try to test it, is if you have an effects loop in the amp, plug your guitar into some kind of a pedal preamp only (or I think a good booster will also work), into the receive of the loop to bypass the preamp. If the power stage still works normally, the problem is your preamp; if not, chances are it's in your power stage.

I do that constantly with bass, but I haven't tried it with guitar. I bypass the preamp of the bass amp because I'm using a signal into dirt, then into a IVP preamp pedal, which makes the amp's preamp redundant - plus that could cause the amp's preamp to blow or damage it. It's a solid state amp, but it's still the same concept.

I hope that helps some, at least to narrow down where your problem is. Good luck, I hope it's nothing big/expensive.

[panoramic]

well it has me hoping it's just bad capacitors is what it does. I'll take it apart later and snap some shots of the guts

[jthomas]

I am not an expert, but I do play around with amp diagnosis. When a working amp suddenly stops working right, it's almost always a bad tube. If you want to start the dx process and have access to spare tubes (maybe a bandmate's if you don't have a spare set) you might replace them one by one in a systematic way and see what happens.

So, for example, pull one of the preamp tubes and put a new one in. If no change, put the original tube back and move on to the next preamp tube, and repeat. When you are done with the preamp tubes, then move on to the poser tubes. If both channels are doing the same thing, it's probably more likely to be the phase inverter tube or at least one of the power tubes. Rectifier tubes rarely go bad, but you never know.

If this process does not produce any improvement, then it'll require a deeper dive... or of you don't have a multimeter or a scope, then a trip to a tech. If you have a multimeter, then the next step would be to check the voltages against a schematic of the amp.

[panoramic]

I did the whole tube thing last night, not the culprit

[ludobag1]

if it is not a tube ,you need a tech cause 8 years since it was controled it it is long ,if you play it often it could be better than if you play it occasionely
caps fails if there are not used and Don't see courant often , an old bass amp blow is filter cap do to no use ,my tech said plug it once a month to make the caps stay good

[andy_tchp]

Filter cap or caps may well have let the smoke out.

Check under the 'doghouse' (removable metal cover that screws up into the chassis behind the preamp tubes), if one has exploded it will be fairly obvious.

Note/warning: These capacitors can contain enough stored energy to cause you serious harm or death, even with the amp turned off.

[panoramic]

what happens when you fry an output transformer? does it still power up and give off some sound or is it just dead?

[somanytoys]

I don't know. I would think that if it's blown, it just wouldn't function, but I can't say for sure that it wouldn't function at a very small capacity.

Also check the fuse/fuses, to be sure none of those have blown. But that means that something bigger probably caused the fuse to blow, so that probably won't be an actual fix. Maybe an indicator, though.

I ran across this, I don't know how far and deep you want to go (depending on your knowledge/experience), but this info could possibly help and it seems to be geared towards older Fender and Marshall types of amps:

http://www.geofex.com/ampdbug/ampdebug.htm

[panoramic]

i've done some minimal amp maintenance and minor repairs before so i mean i'm not 100% inexperienced. I have cleaned out all the inputs and pots before etc. I change tubes myself and have added grounded plugs to older amps. I'm a low level padawan at best when it comes to repair though.

[Jazzmastervsjaguar]

If you do need an amp tech I can not recommend Pete Cage enough. He does great work and his prices a really reasonable. He's out of Damscus MD so not too far from you. Good luck with the amp.

http://www.audiocage.com/services.shtml

[countertext]

My Bandmaster did something pretty similar years ago, and it was caps. The guts were noticeably squeezing out one end of one of them.

[Embenny]

Had a very similar symptom in an amp with dead filter caps. Not 100% specific but they're high not be list of potential culprits.

As Andy mentioned, don't go poking around there if you aren't comfortable. They can release deadly discharges even when powered down because of how much energy they store. Any competent amp tech can check them out though.

[panoramic]

My Bandmaster did something pretty similar years ago, and it was caps. The guts were noticeably squeezing out one end of one of them.

interesting, i hope that's what it is. I'm not pumped on spending more than 150 on it

[somanytoys]

i've done some minimal amp maintenance and minor repairs before so i mean i'm not 100% inexperienced. I have cleaned out all the inputs and pots before etc. I change tubes myself and have added grounded plugs to older amps. I'm a low level padawan at best when it comes to repair though.

That's about where I'm at. I'd love to learn more, but there is a lot to learn, a lot of danger and a large potential to screw things up that can get expensive.

Until I can watch and shadow someone that knows what they're doing and learn more, I figure it's worth the money to pay for someone's knowledge, experience and time to repair something quickly and correctly, and allow me to spend another day above ground by not shocking the crap out of myself.

Hopefully it won't take a tech long to find the problem and fix it, and it will be something like caps and wont' be an expensive fix as far as parts. That was kind of my main point above, that the labor charges will be worth it. Plus, it's possible that they could find other potential problems lurking around, and either fix them, or let you know about them so that if it happens, it's not without warning like this issue.