Guitar amp hum

bluemood · #1 03-27-2010, 01:31 PM

Hi, all I have a peavey valveking that has a slight hum to it ...I have made some mods to it like replace the stock speaker with a Vintage 30 also some preamp tubes really made the little amp very useable...I dummy jack the effects loop seems the help make it quieter...I'm not really sure what else to do, it has a knob in the back called texture which is suppose to give you a class A simulation and a resonance ...The resonance seems to make the speaker vibrate and hum a little more...I'm not sure if better wires and shielding would help what do you guys think?Any advice would be helpful.Thanks

randyc · #2 03-27-2010, 02:45 PM

You get most bang for your buck by replacing the preamplifier tube with others of the same type. There is little consistency in modern tubes and it may take as many as 6 or 7 tries to find "the one".

It's unlikely that internal re-wiring or the like will be much help - no doubt Peavey did a good job of layout and assembly during the design phases.

Good luck - it's a fifty-year-old story and we've all been through the exercise. Go online and buy a half-dozen NOS tubes of the correct type from someone like Antique Electronics - way cheaper than new Chinese tubes and probably way better.

Rather than depending on your ears, BTW, the usual technique when swapping out tubes, is to connect a DVM, adjusted to the lowest AC voltage range, across your speaker leads. Set volume and tone controls to max to get the highest reading on the DVM. Then start substituting tubes, finding the one that produces the least AC voltage at the speaker terminal. NOTE: you're NOT playing anything through the amplifier, of course, just monitoring the AC "hum".

Some folks recommend balancing the bias on the output tubes for best hum performance and that can be helpful. It involves sticking your fingers into some mighty dangerous places, however. I don't recommend this except for experienced techs.

cheers !

billkath · #3 03-27-2010, 04:20 PM

Good advice.
Also-if Randy's advice doesn't get you to where you want to be, take a look at the power supply. Re-capping the supply in it or repositioning it with better shielding can often knock a few dB off hum. Remember, though-it's never going to be silent.

cosmic gumbo · #4 03-27-2010, 06:12 PM

Does it hum with no guitar plugged in?

SamBooka · #5 03-27-2010, 06:42 PM

Quote:

Originally Posted by cosmic gumbo

Does it hum with no guitar plugged in?

Best question in this thread so far..

So.. does it?

TommyD · #6 03-27-2010, 06:49 PM

In the old days when we had plugs without one prong wider than the other, we used to turn the plug over. That usually got rid of the hum. Too bad everything's gotten so "improved".
tommy/

randyc · #7 03-27-2010, 07:24 PM

Quote:

Originally Posted by cosmic gumbo

Does it hum with no guitar plugged in?

LOL, it better or it's not a guitar amplifier

bluemood · #8 03-27-2010, 08:09 PM

Quote:

Originally Posted by cosmic gumbo

Does it hum with no guitar plugged in?

Yes it hums when unplugged and the volume all the way down does not make a difference...For what I read on some of the fourms is that it seems to be a common problem with these amp a plain shame because it's a nice sounding amp...Today I opened it up to see if anything that I can do to it but no chance... I put it in the garage , sence I don't know a tech in town that is any good and would cost... I'm just going to sell at a pawn shop or something not worth the hassle ...Thanks to for all your help.

randyc · #9 03-27-2010, 09:54 PM

As you like, of course. That's a nice amplifier and if you've given up on it you may want to offer it here before hocking

This is a common problem dating back about 80 years. It's one of those "quaint" characteristics of vacuum tube amplifiers, LOL! When they work well, they work well. But the critical components don't get better, unhappily. There's no reason for product improvement because there's no competition.

PS: see Bill's post regarding power supply filter capacitors.