Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: frank57 on January 02, 2011, 01:15:27 pm

Title: Is it normal for a tube amp to have noise, turning controls,nothing plugged in?
Post by: frank57 on January 02, 2011, 01:15:27 pm

This might be a dumb question, but I'll put it out there:
Is it normal for a tube amp to have noise, nothing plugged in when you move the master and gain up?
Or is it case of depends on the amp? Some amps seem dead quite others have noise and hum as you turn them up.

Title: Re: Is it normal for a tube amp to have noise, turning controls,nothing plugged in?
Post by: Cups on January 02, 2011, 01:24:00 pm

Might be dependant on if you have a switch jack or not?

Title: Re: Is it normal for a tube amp to have noise, turning controls,nothing plugged in?
Post by: frank57 on January 02, 2011, 02:42:29 pm

Pretty sure it's a cliff jack switching.
Quiet when you pull cord out, but noise if you turn controls.

Title: Re: Is it normal for a tube amp to have noise, turning controls,nothing plugged in?
Post by: rafe on January 02, 2011, 05:44:02 pm

I think it depends on the amp, the type of noise, the degree of noise and so on....sometimes they pick up outside issues .... lights, computer... your electricty supply itself. It could be a bad component in the amp.... tube, cap ,resistor,solder joint,potentiometer.... I have amps that are really quiet and some that are not.....I know that doesn't really answer the question , but we would need to know more about the amp and the noise..... :dontknow:

Title: Re: Is it normal for a tube amp to have noise, turning controls,nothing plugged in?
Post by: LooseChange on January 03, 2011, 04:40:46 am

Tubes and circuits make some noise. If there are some gain stages before the power amp that don't have thier grids grounded (like a volume control on zero) you will hear noise.

Title: Re: Is it normal for a tube amp to have noise, turning controls,nothing plugged in?
Post by: frank57 on January 03, 2011, 08:03:28 am

It's one of those jet city 20 watt combos.
But now I'm having big time second thoughts on it.
I can see why they're being dumped.
I'm leaning towards just getting rid of it and move on from pcb stuff.
Crappy tubes and hiss. I wasn't expecting that.
Factor in new tubes and maybe  dc power and it's not exactly cheap anymore.
Even then, there might still be some hiss going on.
I don't know if I want to go down the round of an amp with noise after high noon
on the dials.

How much of that is normal I have no idea.
The schematic is fairly close to their head but with reverb.
The tube layout is odd as well and not that easy to change.
Chassis is vertical with tubes pointing horizontally towards the speaker.
If I remember a Marshall had such an arrangement with  disastrous results.
The schematic is essentially an Atomic 16 with reverb.
This is what I found for the jet city head it's essentially the same.