New Tube Amp Problem

K

KoSTheKing

New member
Hi Everyone, thanks to the advice to some of you on this forum, I recently got a 6505MH - my first tube amp.

It arrived today, and I seem to have a problem, it's almost inaudible at max volume.

I did let the tubes warm up for about 20 minutes before playing, and set the built in attenuator to 20W.

Oddly, when I plug my guitar straight into the FX loop it sounds like it should, nice and loud, it's only when I plug it straight into the pre-amp first is when it's quiet.

The only thing I think could be the problem is that I didn't replace the fuse, I ordered it from the US, and the manual says that you've gotta replace the fuse from F2AL250v -> F1AL250v when using the 220v circuit. But even then that doesn't make much sense.

What else could be the problem?

P.S incase anyone's worried, I wont be using the amp again until I replace the fuse, I just wanted to make sure it worked properly first.
 
Re: New Tube Amp Problem

A preamp tube? Are there any other differences (besides fuse and voltage) in the preamp between US an overseas models?
 
Re: New Tube Amp Problem

Jump out the effects loop with a patch cable

It usually doesn't happen with a brand new one but that's probably what is happening
 
Re: New Tube Amp Problem

ehdwuld said:
Jump out the effects loop with a patch cable

It usually doesn't happen with a brand new one but that's probably what is happening
Click to expand...

I just plugged the patch cable in, but I'll only be able to test it tomorrow, and hopefully I should have the replacement fuse then.

Does this usually happen on old amps? Because technically it's not brand new, but it is manufacturer refurbished, and it doesn't seem like something they'd miss.
 
Re: New Tube Amp Problem

yeah, maybe your EFX loop in not disengaging.

Im not sure how that amp is manufactured. If it has circuit boards and ribbon cables, one may have come unseated.
 
Re: New Tube Amp Problem

If the patch cable does not do it, next on my list would be the preamp tubes. I would usually swap them one by one to see if there’s a faulty one. Do they glow normal?
 
Re: New Tube Amp Problem

Blille said:
If the patch cable does not do it, next on my list would be the preamp tubes. I would usually swap them one by one to see if there’s a faulty one. Do they glow normal?
Click to expand...

The Power amp tubes do, but I can't see if the pre amp's are, because they seem to have some sort of casing.
 
Re: New Tube Amp Problem

Not sure what's going on with the amp, but difference in the fuses makes sense. Since you are double the voltage (220 vs 110) you want to limit the current to 1/2 the amount. Power = Voltage * Current, so you are keeping the input power limit the same by cutting the input current limit in 1/2 (1A for 220 vs 2A for 110). Basically you are potentially risking damage by not changing the fuse, although I doubt it has anything to do with your current problem since the output section seems to be working.
 
Re: New Tube Amp Problem

KoSTheKing said:
The Power amp tubes do, but I can't see if the pre amp's are, because they seem to have some sort of casing.
Click to expand...

If it’s like a metal sleeve it will come off easily after you rotate it a bit counterclockwise. Perfectly safe to do. Go to minute 2:05 here https://youtu.be/7JHwYLLYvNE

Then if you turn it on and one doesn’t light up or lights up blue that’s a sign it’s bad. Also if you remove the sleeve and there’s no tube that would be bad lol
 
Re: New Tube Amp Problem

If you check the tubes you may have to look close. Darken the room. Some preamp tubes have spiral filaments making it harder to see if they are glowing. If you can't see a glow, don't assume it's dead. Let the amp warm up for a while and then check to see if the preamp tubes are warm/hot (not with your fingers), you should be able to feel some radiant heat. Even if the heaters are working, it's no guarantee that the tube is conducting signal, but it's a good start.
 
Last edited:
Re: New Tube Amp Problem

Opened the amp, there's a busted pre-amp tube ;/

Because it's probably cheaper and less time consuming to replace it myself than spend $50 on shipping it back, I'll replace it myself.

I assume that if I use the same tube type I won't have to rebias it?

Also is it safe to use in this condition?
 
Re: New Tube Amp Problem

KoSTheKing said:
Opened the amp, there's a busted pre-amp tube ;/

Because it's probably cheaper and less time consuming to replace it myself than spend $50 on shipping it back, I'll replace it myself.

I assume that if I use the same tube type I won't have to rebias it?

Also is it safe to use in this condition?
Click to expand...

Preamp tubes don’t need to be biased. Only power tubes do.

Replace the tube with the same type (12ax7 most likely). Don’t use the amp until it’s replaced.

Here’s where I usually buy my tubes:

Tubedepot.com

I’m assuming you are in the US. If not there are several good tube dealers in Europe too.
 
Re: New Tube Amp Problem

Gtrjunior said:
Preamp tubes don’t need to be biased. Only power tubes do.

Replace the tube with the same type (12ax7 most likely). Don’t use the amp until it’s replaced.

Here’s where I usually buy my tubes:

Tubedepot.com

I’m assuming you are in the US. If not there are several good tube dealers in Europe too.
Click to expand...

Thanks, I unfortunately don't live in the US, hence why shipping is so high, but I have found a place to buy the tubes.

And thanks to everyone else for trying to help me solve this :)
 
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