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Post subject: DRRI Hum!
Posted: Mon Oct 01, 2012 1:27 pm
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My DRRI has a hum and hiss problem. It hums even if nothing is plugged into it. The volume knobs seem to control the amount of hiss. I've tried troubleshooting it as best as I could and here are the results:

1) Pulled the phase inverter and the hum and hiss disappeared.
2) Pulled V5 with no change.
3) Pulled V4 and the hum and hiss disappeared.
4) Replaced V4 tube with different 12AX7 and 12AT7 but hum and hiss remained.
5) Pulled V3 with no change.
6) Pulled V2 but Normal channel volume still controls hiss.
7) Pulled V1 with no change.

I have no idea what could be causing this. Any and all help is always appreciated!

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Post subject: Re: DRRI Hum!
Posted: Mon Oct 01, 2012 2:21 pm
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Penguin, welcome to the Board! I believe that one-half of V4 is the reverb recovery tube. Try pulling both reverb lines off the back of the amp with V4 in, and see if the noise changes. If so, maybe the cables connected to the reverb tank are loose or the contacts need cleaning.


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Post subject: Re: DRRI Hum!
Posted: Mon Oct 01, 2012 3:48 pm
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I will try that out when I get home. I forgot to mention that the reverb knob acts like a hum control...

I just unplugged the reverb wires from the chassis. The humming got a lot worse as I turned up the reverb knob.

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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 2:47 am
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Penguin_21 wrote:
...
I just unplugged the reverb wires from the chassis. The humming got a lot worse as I turned up the reverb knob.


It is normal , no reverb plug in , tube input is like an antenna.

Look like you have a bad ground ( wire or RCA connector on amp or reverb tank ) or bad tube in reverb section.
It is not the tube if you try a good one .

Could be some wire - wrong routing. Did you work in the amp before this trouble ? Or did you see this amp working well before ?


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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 3:04 am
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I just did the Fritz mod but the amp has always hummed and hissed. Removing V6 and V4 gets rid of all the noise. Could it be a bad rectifier tube?

http://music-electronics-forum.com/t20885/

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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 3:14 am
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I don't think it's the rectifier. I mean, you can always try another known, good 5AR4/GZ34 just to test your question. But, if you pull pre-amp tubes (V4 or V6) and the noise goes away --- that "rules-out" a rectifier or output tube issue. Right?

I think Stratele is correct. It's somethning about the dressing or components around V4. Or wiring to the tank. It's prolly not V6--- as you pull V4 and noise goes away, even though V6 is still in the amp. Right?

Good luck!


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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 3:42 am
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That's correct. The noise goes away if I remove V4 while V6 is still in the amp.

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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 12:45 pm
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Penguin_21 wrote:
Could it be a bad rectifier tube?


No .

If you are sure before the Fritz mod it do some noise , it is not the mod.
But before that ?
This amp was never quiet ? Nobody work inside before ?
Is there are any wire around the reverb circuit in the amp you could move a little bit ?

Or your 6L6's are unmatched . More than 15 to 20 ma between them can make noise.


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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 1:45 pm
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Your using 6L6's?

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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 1:54 pm
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I'm using Tung Sol 6V6's, not 6L6's. The previous owner had the amp biased a little hotter. But why is the noise being controlled by V4?

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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 2:31 pm
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Hou-Tex wrote:
Your using 6L6's?


Oups ! Sorry so much amp use 6L6 , I should write 6V6. But yes you could put 6L6 , amp will be cleaner.


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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 2:36 pm
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Penguin_21 wrote:
I'm using Tung Sol 6V6's, not 6L6's. The previous owner had the amp biased a little hotter. But why is the noise being controlled by V4?


Problem look to be close to this V4 . Why I talk about unmatched 6V6 ? It's good to know. But it is not your case.


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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 4:28 pm
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I'm new to tube amps so my suggestion may be off course. But being an old dude, I would check for connection issues first.

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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 4:38 pm
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Hou-Tex wrote:
I'm new to tube amps so my suggestion may be off course. But being an old dude, I would check for connection issues first.


And check lead dress too


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Post subject: Re: DRRI Hum!
Posted: Tue Oct 02, 2012 4:58 pm
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stratele52 wrote:
Hou-Tex wrote:
I'm new to tube amps so my suggestion may be off course. But being an old dude, I would check for connection issues first.


And check lead dress too


I don't know what that is, but I would start with the simple things likes connections. Use some contact cleaner, whatever in the areas you question.

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