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Noise problem in 572-10 PP amplifier

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The heater thing was a long shot... damper diodes are rated for the cathode being +900V wrt the heater so the heater could also be grounded in this case.

I still don't know if I would put them on the same string as gain stage tubes. I guess maybe if they had a low impedance ground.

Good to hear the noise has gone. It must have been the wiring?

Cheers,

Michael
 
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The heater thing was a long shot... damper diodes are rated for the cathode being +900V wrt the heater so the heater could also be grounded in this case.

I still don't know if I would put them on the same string as gain stage tubes. I guess maybe if they had a low impedance ground.

Good to hear the noise has gone. It must have been the wiring?

Cheers,

Michael

Good to know, and FWIW I generally don't put rectifier heaters on the same string as small signal tubes, but it has been done in the past - most commonly in tubed tuners and pre-amplifiers. (Scott and Fisher both did this)
 
My photo host has been down for a while so I am only
now able to post a shot of the underside

816917746_yzL2V-L.jpg



The lower left hand corner of the amp is an electrically noisy place.
Cleaning this up and moving the feedback line and rotating the pot so the terminals were as far away as possible from where the wires from the power transformer go through thetop plate was the cure.

Noise is about 5 mV PP pretty much a combination of 60 Hz, something else and I can see the spike still is lurking although at much lover levels.

I am using AC on the 572-10's filaments.
Still a lot to do here.
I want to remove the two black resistors that are hanging in space and use one of those gold aluminum ones. I'll form a L bracket to hang it on and sink a bit of heat as well.

There are numerous other little problems that will be adressed as I go.

Next thing to work on is square wave response.
It looks pretty good right now with a bit of peaking on the leading egge but no ringing, just a gradual tilt which is not too sharp.

Thanks again for the help, suggestions and inspiriation to persevere and tackle the issue.

Cheers!
 
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