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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: RE: Bias source from B+ or seperate trans, which is better? posted by drlowmu on August 8, 2014 at 17:15:34:
I believe the spikes from rectification not only affects the forward B+ supply but is also reflected back into the power transformer and cross contaminates all th secondaries.
To that end I placed three snubber caps, .1 uF, across the legs of the filament leads and ground, hoping that the effect would have some change in the B+. It certainly did. Everything became significantly warmer and fuller with an increase in midrange dynamics and detail. Cheap and very effective.
I only had 120 VAC rated caps so I couldn't place them on the B+ leads.
Also one of the major issues with bias circuits is to adequately buffer it from the ground. In most cases, the adjustable pot ( thinking Dyna circuits here) simply has a a cap to ground. This allows the bias voltage to swing a bit more than I prefer. I place a simple cap across the resistor to ground with great results, better resolutions and dynamics. The cap ( a small one, 5 UF is OK and electrolytics certainly work very well) buffers the bias circuit extremely well. You can see this in metering out the bias. Turn the knob and the voltage moves significantly slower, thus maintaining better control over the signal, IMHE.
Using this cap actually eliminates the need for a separate full wave bias bridge, although it should work there too.
YMMV and certainly FWIW
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- Interesting comments - unclestu 18:19:03 08/09/14 (0)
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