[doctorcilantro]

Dual mono 6V6 amp.

Last month, I'm sitting in the sweet spot about 9-10 feet away and right channel is buzzing away. Left is dead quiet. I first fully swapped ALL  tubes. Noise remained. Then I swapped speaker wire and the noise moved over to the left. it's not a ground loop or AC on the line, as I have a DC blocker and a PS Audio P3; all other tube amps and systems dead quiet.

Output terminals on right amp...measure 13.8mv AC with the "hum" test. Left channel is 3.3 mv AC wide open. I was told you don't know what freqs you are measuring. True. But there is audible noise in conjunction with this test!

Using my HE500 phones, right channel wide-open at 20, there is tiny hum and buzz coming and going, mostly on and drops off to just hum rarely.

Attnuator settings
0-12 hum starts at 7
13-16 buzz gets louder and louder until same amplitude
17-20= buzz gets silent quickly going towards 19, but at 20 comes back strong

I'm totally confused. The left channel does not act this way with the noise on it which is much less overall. I have to go to 14-15 on left to hear any hum at all and there is no buzz.

Sent amp back and given ALL CLEAR by manufacturer. Was charge almost $200 for new tube socket and return shipping to fix pops on attenuator (could have told me allI needed to do was tighten pins which I had forgotten about)...

Now the amp is dead and manufacture states:

"If the right keeps blowing the fuse, remove the rectifier tube on that channel and try again.  If it blows the fuse without a rectifier tube installed then the power transformer has failed due to a severely shorted rectifier tube at some point."

I can't help but think there is an underlying problem. Especially since he amp was back and checked out fine by builder last month after I reported the hum problem....

thoughts?

[avahifi]

The best way to chase down hum issues from your audio system is to start by simplifying the system.

First, shut off the system and disconnect the interconnect cables at the power amplifier between the preamp and the power amp so only the speakers are connected to the power amp.  If you have shorting plugs, insert these into the power amp input RCA jacks.  Turn on the power amp.  If the hum/buzz is now gone, then the power amp is not the culprit.  If the hum-buzz remains as before then the problem is the power amp or possibly RFI pickup in the speaker wires (possible from a nearby radio broadcast station or similar.  Twisting your normal two conductor speaker wires three turns per foot chucking the wires into an electric drill will sometimes resolve this issue.

If the hum is not the power amp, then turn it off, reconnect the amp to the preamp, disconnect all sources from the preamp and try again.  If the noise now reappears, the issue is with the preamp, poorly shielded interconnect cables between the preamp and the power amp, or some kind of ground loop issue.  In this case shut the system down, disconnect the AC power cord from the preamp and try again.  If the hum still is there then poorly shielded interconnect cables may be the issue.

If the hum is gone with just the preamp and power turned on and no sources connected to the preamp, then reconnect sources one at a time until the noise reappears.  This can help identify the problem.

I hope this helps.

Frank Van Alstine

[doctorcilantro]

I've done all those tests. The dual mono amp shares one PSU. There is a problem in the right channel amp.

[Davey]

If it shares a PSU, then it's not a dual-mono amp. 

Regardless, if you've disconnected all inputs to the amplifier and you still get hum in the right channel, it suggests a problem in the amp.

However, your initial description is somewhat confusing because you indicate the hum volume is affected by your volume-control (attenuator) position.  Frank is surmising (I think correctly) that you may have and additional issue possibly involving your interconnect configuration.

Cheers,

Dave.

[doctorcilantro]

Thanks, all I know is that it is swapping tubes and cables shorting plugs doesn't change where the hum/buzz is located....

I troubleshot an DC riding AC problem and posted the resolution on AC. This problem has been present throughout, and distinct from that.

It is a dual-mono amp....maybe it shares one fuse? Thanks for the assistance all.

"employes fully tube regulated input and output stages in a fully dual mono configuration using two independent power supplies. "

If it shares a PSU, then it's not a dual-mono amp. 

Regardless, if you've disconnected all inputs to the amplifier and you still get hum in the right channel, it suggests a problem in the amp.

However, your initial description is somewhat confusing because you indicate the hum volume is affected by your volume-control (attenuator) position.  Frank is surmising (I think correctly) that you may have and additional issue possibly involving your interconnect configuration.

Cheers,

Dave.

[doctorcilantro]

"Long life - all internals are way overbuilt, there's just nothing inside to fail. Expect 50 years of use out of it without problems.

Low power - the amplifier can't blow itself up if the speakers are unhooked, nor can it blow up a speaker if a tube shorts or fails.  There is really nothing you can do to hurt it or your speakers."

[HPDJ]

OK wow....you have not stated the manufacturer of said amplifier, but if it is who I think it is then I had the very SAME amp and with exactly the SAME issues. I'll be polite and won't call them out but I feel for pain..

PM me if you'd like  

[doctorcilantro]

sigh...pm sent

[avahifi]

Did you know that if you do a Google search for the phrase quoted above, it brings you right to the manufacturer of the amplifier in question. 

Frank Van Alstine

[doctorcilantro]

yes, that is how google works

and it sounds like many others having this issue and we are not being helped,nor is there any clarity that others have had similar issues. I wait days for responses.

It's going back and then up for sale after repair.