Gallien-Krueger 400B - Leaking Transformer/No Sound

[louloomis]

Hey Everyone,

I have a 400B bass amp from the early 1980s. Great amp. The transformer was at some point (possibly the present) leaking ooze (but not a lot). The power light never went off, but the sound became faint and fizzy and then there was no sound.

Is the cause of this the transformer, or is there something causing the transformer to leak which is/is not also causing the sound loss. Even if the sound loss problem is fixed and the cause of the transformer leak is fixed, does this mean that the amp is fixed or is the transformer leakage a sign that the amp is doomed?

Thanks,
LL

[52 Bill]

Is the cause of this the transformer, or is there something causing the transformer to leak which is/is not also causing the sound loss. Even if the sound loss problem is fixed and the cause of the transformer leak is fixed, does this mean that the amp is fixed or is the transformer leakage a sign that the amp is doomed?

Thanks,
LL

Leaking transformers are usually caused by heat. If it got hot, there may have been a problem with the amp or it may have just failed for some reason. The only way to find out is by testing the amp and the transformer.

What sort of test equipment do you have available? What sort of skill set do you have?

[louloomis]

Thanks a lot for the response. I don't have any test equipment. I can solder and maybe use a multitester, but that's it (skill-set-wise, per your question). The repair guy quoted me 125-150 to fix the problem, but he didn't notice the very obvious transformer leak, which is what is making me unsure that this repair is going to work out.

Any additional direction would be great.

Thanks.
LL

[52 Bill]

Thanks a lot for the response. I don't have any test equipment. I can solder and maybe use a multitester, but that's it (skill-set-wise, per your question). The repair guy quoted me 125-150 to fix the problem, but he didn't notice the very obvious transformer leak, which is what is making me unsure that this repair is going to work out.

Any additional direction would be great.

Thanks.
LL

Is the quote you got based on actual testing or just a blind guesstimate? If the transformer is still viable then it could cost 125-150 to fix depending upon what's wrong with the amp. Was there any breakdown of the cost like 100 labor and 50 for parts?

If the amp still powers up but doesn't make sound, there are a few things that you can test before yo turn it over for repair. I don't remember if that model has one or not, but if it has a FX loop try jumpering the in to the out with a spare patch cable. Does the sound come back? How about if you plug your guitar into the return jack, any sound?

[louloomis]

I personally believe the quote was based on a blind guesstimate even though the repair guy had the unit in had for 2 weeks. Due to the fact that the transformer issue was not spotted, I think he might not have checked it out thoroughly - hence the "blind guesstimate". There was no breakdown of parts vs. labor.

The amp still powers up but doesn't make any sound. There is no FX loop on this model.

Any other thoughts would be appreciated very much.

Regards,
LL

[52 Bill]

The amp still powers up but doesn't make any sound. There is no FX loop on this model.

Is there any sound at all, hum, hiss, etc.? Does changing any of the controls make any noise through the amp at all?

The next steps would require you to start testing things with a meter while the amp is powered up. Is this something that you are comfortable with doing?

GK generally didn't use internal fuses, but you should check to see if there are any fuses on the pc board that may be open. The power supply would be the first thing that you need to test.

Edit: I just Googled photos of your amp, does your amp have a preamp out and power amp in jack set? Try the spare cable there.

[louloomis]

There is only a very slight hiss....almost inaudible. I'm really not comfortable testing the amp with a meter while the amp is powered up.

The power light is on - don't know if this affects your comment about fuses and testing the power supply...

Yes, my amp does have a preamp out and power amp in jack set. By "try the spare cable there" - I assume you mean that I should try to isolate the problem to the preamp section or power amp section of the amp. I wish I thought of this before. Thank you for this insight!

Regards,
LL

[52 Bill]

There is a switch on the power amp in jack that normally closes and sends the signal from the preamp to the power amp. These contacts will get dirty, oxidized and break the contact from pre to power amp. If you plug a spare cable from the pre out into the power amp in it will take the place of the normally closed switch and restore the sound.

Even though the pilot led turns on, the power supply may not be working at 100%.

And yes, isolating the problem to either the pre or power amp will help in finding the solution.

[g1]

Was there a time you saw the transformer without the "leaking ooze"? If not it could have always been there. If you are not sure it wasn't there before, forget about it.
I'm pretty sure that model of GK had a thermal fuse in the transformer, so if it had overheated enough it would be dead and the amp would not power up at all.
Most commonly they had issues with pots and jacks. Your other post mentioned scratchy pots & squealing. Cleaning and resoldering the pots and jacks and connectors may solve your problem.

[louloomis]

Hi. No I didn't see the transformer before it "leaked ooze". You could be right - it might have always been there. Interesting what you said about the thermal fuse in the transformer. The amp is powering up, for sure. Not sure if it's full power, though.

The other post (pots/squealing) is about another G-K bass amp that I have from an era about 30 years newer - just mentioning this factoid to be on the safe side, although you may have already known that.

Thanks again for all the help on this.

LL

[g1]

Oops, sorry I didn't see the difference in the model numbers for your 2 posts. And this is a 400B not RB so it's really old (and collectible to some ).
I wouldn't worry about the transformer. Please do as 52Bill suggested and try to isolate the problem to pre or power amp, by way of pre out and pwr amp in jacks.