I have upgraded the capacitors in the output stage of my tube buffer. My last change was to swap an Audyn .22 uF @ 630volts for the stock WIMA .22 uF @250 volts. After the swap there was a hum that would increase with the volume but all but went away when I touched the cap. What is going on here? I have put the WIMA caps back in and the unit is silent again. Are the Audyns' bad? They test fine on the cap tester.
Try putting them in reversed. This may be an outer-vs-inner foil issue, especially if the "buffer" is a sketchy design.
IMO, what you did is not actually an upgrade, but no need to reopen that can of worms.
IMO, what you did is not actually an upgrade, but no need to reopen that can of worms.
Thanks Si, reversing the caps was the first thing that came to mind but it did not work. You may be right about the sketchy design. It is a music fidelity x-10. Just can't see why the WIMAs' work and the Audyn will not.
Are the Audyns physically much larger than the Wimas? If so, you could have extra stray capacitance which could lead to hum pickup or parasitic oscillation. The fact that it went away when you touched the cap is a classic symptom of RF oscillation - your body added enough resistive loss to kill the oscillation. If it were normal hum pickup then touching the cap would probably make it worse.
Two possible solutions:
1. use normal size caps
2. add resistors, either grid or cathode stoppers (or both)
Two possible solutions:
1. use normal size caps
2. add resistors, either grid or cathode stoppers (or both)
You say "caps", so more than one. To be scientific, you might change them one at a time to see which is causing this. it is possible it isn't the brand causing the problem, but a particular cap could be defective. Did you try more than one of the new style in each position? Or if none of the new caps is defective, at least knowing which cap is causing the problem would help us to understand why it does so.
The capacitors are rated the same as the WIMA capacitors that I have replaced.
The WIMA capacitors are .22uF @250 volts and the Audyn capacitors are .22uF @ 630Volts.
These capacitors are in the signal path between the dac and the tubes. I have tested the capacitors with a tester and they are at exactly .22 uF.. The only real difference is that I cannot attach these as close to the board as the WIMA caps.
Thank you,
Ken
The WIMA capacitors are .22uF @250 volts and the Audyn capacitors are .22uF @ 630Volts.
These capacitors are in the signal path between the dac and the tubes. I have tested the capacitors with a tester and they are at exactly .22 uF.. The only real difference is that I cannot attach these as close to the board as the WIMA caps.
Thank you,
Ken
Have you tried putting a weight on them, conductive and/or non-conductive?
I guess you have the question if it's worth it, if you can figure out how to keep them in. DF96 probably solved it.
I guess you have the question if it's worth it, if you can figure out how to keep them in. DF96 probably solved it.
Thanks for the replies. Fahey is right. I'll keep the Wima capacitors in place. It sounds just right with them in place. Just got carried away with the upgrade issue. It is a hoot to play with this stuff though...
Thanks again,
orca1993
Thanks again,
orca1993
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