Just got a used tube amp and having problems. Need help.

[strangelove]

Hello all. I just bought a used Woo Audio 4 Upgraded amp from a fellow headfier. It's a very lovely sounding amp, I really like it a lot. However I noticed a low level static hum that seems to be getting louder. To describe it:

there is a low level static hum in both the Lt and Rt channels that is noticible when there is no sound playing (even when no source is attached) or very soft passages. It's not loud enough you can hear it when music is playing. There's a high/low impedance switch and it occurs with either selected. There is also a louder intermittent fluttering static noise that only occurs in one channel. I tried switching all the tubes from left to right (there's two each of three different tube types). I narrowed it down to the static sound flips from Lt to Rt when I switch the location of the largest of the tubes (not sure which number it is). This makes me think that part of the problem may be from a bad tube. The rest I'm not sure of.

I emailed Woo Audio but didn't get much help. Jack said the amp should be dead silent at rest and thought it could either be bad tubes or something with the amp. The previous owner claims it worked upon shipping so maybe something happened in transit. Another problem is the previous owner sold it to me claiming there were two sets of tubes included (which now he says he was mistaken about). In fact there was only one set of the 6C19 and EZ80 and two pairs of ECC82 and one pair of ECC88 (which I don't know which one they are a replacment for).

So I'm kind of at a loss where to proceed from here. Looking on Ebay replacement tubes are probably going to cost around $50-60 bucks which stinks because I bought it believing it was going to come with the extra set of tubes I'd need if anything went wrong. Then if I get new tubes and still have the problem I'll have to send it off to get fixed which I'm sure won't be cheap because the shipping alone will be $40-50 each way.

Anyone have any ideas what the problem may be and where to go from here?
Also, can using the amp in this condition make the problem worse? I'd imagine so, so I've stopped listening to it as the noise seems to be getting louder.

[takezo]

try it using an electric outlet from a different part of your home. are you using any sort of voltage filtering or cleaning? if that doesn't help, send it in to wooaudio. if the static humming is from both channels, it's probably an issue with the heater or grounding in the amp and less likely that the tubes for both channels are causing it. it'll probably cost you
some money, besides shipping fees, if it's no longer under the one year warranty. good luck.

[Skylab]

Sure sounds like a tube issue. You might need a back-up set anyway if you plan to keep the amp.

[WalkGood]

I had a low level hum as you describe once, did as takezo mentioned and used a different electrical outlet, it was a grounding issue with the outlet, either way it solved my problem. Later I fixed the outlet and it works now too.

[Redcarmoose]

My first was a Woo Audio 3. It has made about 3 wierd sounds, only on warm-up. Go find someone with a good tube tester. Tube testing is easy just check the values on the tube, put them in right spot. Don't buys new tubes till you know what is up. If all your tubes are good then take it to a repair guy. Another question I have is about your source. You know about phono grounds and cable breaks right?
.

[strangelove]

I'll try a different outlet when I have a chance. I'm using a Belkin power strip with supposed "filtering" but I doubt it's anything special. My source is a Denon 3930CI connected by 1m cables (I've tried various ones all with the same result).

Any potential dangers from continuing the use the amp in this state?

[takezo]

danger? probably not. unless you see sparks...

the belkin power strips most likely adds noise or humming to your source. try it without
the power strip. you may be surprised. try the set-up at another place, work or friends
home. if nothing changes, it's most likely the heaters and/ or the tubes.

*don't bother with the source or interconnects since you said the amp hums even when
source is disconnected. the fact you mentioned that the hum seems to be getting louder
may point to tubes in the process of shorting out. have you tested the tubes for shorts
with a tube tester? if not, try getting your hands on more tubes to see if it helps.

[strangelove]

Just tried the amp on a different outlet in a different room without any power strip. Sounded the same.

[takezo]

if possible, please try the wall outlet at the other part of the home. sometimes, rooms
adjacent share the same outlet wiring...

[strangelove]

The 2nd outlet I tried was in a different room. The farthest in my apartment I could find from the original.

[takezo]

with no source attached, but only the headphone, does
the hum sound increase when you turn the volume dial up?
if the hum increases, it's a tube issue. if not, it's most likely
a heater, and/or transformer issue related to powersupply. dried
out caps or bad resistors usually affect only one channel but
it's possible caps from both channels are bad. a bad tube
causing hum is a tube with shorting issue, but the hum will
increase or decrease when you change the volume dial.

one thing you can still do is try the amp, without any source,
at another location like a friends home. that should confirm
whether or not it's a simple dirty ac from you home or an issue
with the amp or tubes. good luck.

[strangelove]

The noise occurs in both channels with no source attached and doesn't change when changing the volume knob. The fluttering static is only in one channel and changes with moving the tubes from Lt to Rt so I think that part at least is from a bad tube. I'm looking into trying to get my tubes tested.

[Anouk]

Wow I am so shocked by this, since I am having the EXACT seem problem! two kinds of hum one low level and one higher level (meaning lower frequencies and higher frequencies) i also have static in m left ear and sometimes random noises. I didnt notice them at first, i was using a more sensitive headphone but now it is quite clear and VERY irritating, I have a wa2 second hand as well. Someone pointed me to this thread, i started my own about it here:
grounding issues
Op, I am VERY interested to know, where you ever able to solve this issue because it really gets me.
Greetings, Anouk,

[Anouk]

Oh yea, mine is connected to a wall outlet no power strip, i hear static in my left ear and two kinsf of hum one of whichincreases ifi highten the volume. there are also random noises. I will have new tubes this week and I hope they will fix part of it.
Greetings, Anouk,

[Anouk]

Hello, someone suggested in a pm to try tube dampers. I am, very new to tube amps, anyone know if this might make a difference?
Greetings, Anouk