Systemic Development > Amplification and Preamplification
Tube circuit question
steve:
--- Quote from: tmazz on April 20, 2021, 10:27:57 AM ---That's a good point Bob. I wonder if the problem was not so much the polarity as it was the connection and in then process of doing the lead swap the hum went away not so much because of the polarity but because the connections were done properly.
A number of years back I had an intermittent hum problem with my Moscode 600. Brought it over to Scott and he found the problem in no time flat, a cold solder joint on the underside of the board. Heated it up to reflow the solder and it has run like a champ ever since.
Still wondering if any of ur tube design experts had any thought ? Steve? Bill?
--- End quote ---
Hi T,
When I designed my personal phono stage, the filament circuit was completely isolated from everything except for one connection at one point. There are no common lines of filament/power/signal grounds.
That one connection occurs when floating the filament circuit above ground with the resistor divider network to provide a positive filament to cathode potential. (Stay within the filament to cathode voltage limits.)
Even then, location of the resistor grounding is crucial.
But as previously mentioned, I also do not know the circuitry/layout of "your" particular situation.
cheers and hope this helps.
steve
P.I.:
--- Quote from: steve on May 13, 2021, 09:38:25 AM ---
--- Quote from: tmazz on April 20, 2021, 10:27:57 AM ---That's a good point Bob. I wonder if the problem was not so much the polarity as it was the connection and in then process of doing the lead swap the hum went away not so much because of the polarity but because the connections were done properly.
A number of years back I had an intermittent hum problem with my Moscode 600. Brought it over to Scott and he found the problem in no time flat, a cold solder joint on the underside of the board. Heated it up to reflow the solder and it has run like a champ ever since.
Still wondering if any of ur tube design experts had any thought ? Steve? Bill?
--- End quote ---
Hi T,
When I designed my personal phono stage, the filament circuit was completely isolated from everything except for one connection at one point. There are no common lines of filament to power/signal grounds.
That one connection occurs when floating the filament circuit above ground with the resistor divider network to provide a positive filament to cathode potential. (Stay within the filament to cathode voltage limits.)
Even then, location of the resistor grounding is crucial.
But as previously mentioned, I also do not know the circuitry/layout of "your" particular situation.
cheers and hope this helps.
steve
--- End quote ---
:thumb:
In many ways circuit design is lie real estate: Location, location, location. I know: been there, done that.
tmazz:
Thanks for you input guys. I kinda fatigued that this would be more involved than just a quick simple answer.
I do not know much about the particular amp that had this problem. I don't even personally know the guy who owns it. He was just a guy I was chatting with online.
My interest in the topic was strictly from a point of intellectual curiosity.
Thanks again for sharing your ideas.
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