Noise, Signal Tube or Power Tube.
- Thread starter acass
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primosounds
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Well, if you suspect it is the tubes you can pull the signal tubes 1 at a time starting from the input and see if that makes go away. If it is still there after pulling the tubes up to the power tubes then it is most likely not the tubes.
how long has that hum been around, did it just suddenly appear? Try shorting the input of each monoblock and see if the hum remains, this should generally tell if the hum is external or internal to each monoblock.
Also, have you made any interconnect changes lately?
Also, have you made any interconnect changes lately?
I wasn't sure it was safe to pull the signal tubes as VTL warns against running the Amps with no interconnects
The amps have been sat for a while so I'm not sure if it had the hum before. At 75 my hearing is shot so I have to have my ear close to the speakers to hear it but my son in law was visiting and he spotted it as soon as I turned them on. I've changed the source from cd to tuner, I've changed preamps and I've tried various cables but the hum remains. It has a bit of a hiss to it so I think it's a tube also it is a different frequency in each amp. I will try another pair of mono blocks and see what I get from them.
If there is a balance adjustment or individual bias adjustments per-tube, are they set correctly? An imbalance in the output stage can cause hum.
Knowing the frequency of the hum will help too. 120 hz is power supply, which is also what an imbalance will be. 60 hz will be heater-cathode leakage, more likely one of the small signal tubes.
Quick and dirty way to rule out the small tubes is to simply remove them and see if the hum is still there. If it is you know its not them.
Knowing the frequency of the hum will help too. 120 hz is power supply, which is also what an imbalance will be. 60 hz will be heater-cathode leakage, more likely one of the small signal tubes.
Quick and dirty way to rule out the small tubes is to simply remove them and see if the hum is still there. If it is you know its not them.
personally, I would not pull the signal/preamp tubes and run the amp. Depending on the circuit, this may in fact induce noise or cause other issues. It is always best to try a different set of tubes from your stash.
Here is an interesting 'fix' for VTL designed amps. http://www.diyaudio.com/forums/tubes-valves/184161-vtl-hum-3.html, top of the page.
I am not familiar with VTL amps, but for interest sakes, the signal ground on all my circuits are 'lifted'. I use an RC circuit instead of the diodes as describes in the above article.
Here is an interesting 'fix' for VTL designed amps. http://www.diyaudio.com/forums/tubes-valves/184161-vtl-hum-3.html, top of the page.
I am not familiar with VTL amps, but for interest sakes, the signal ground on all my circuits are 'lifted'. I use an RC circuit instead of the diodes as describes in the above article.
primosounds
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If the amps are out of warranty , what are you going to lose by checking the circuit via removing the amplification devices in a logical step wise fashion. You might not want to have the amp hooked up to your best speakers but as long as they have a load it should not be a problem. It would be like the amp has a dead tube.
CopperWizard
Super Member
One hums a little different, try swapping the tubes and see if it follows to the other amp. Signal tubes first.
