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shared versus separate filament suppies....

Posted by Vinnie (A) on January 20, 2007 at 06:05:22

I have been going through the archives trying to find info on the pro's and cons' of shared vs separate filament supplies and the answers are all over the place. I am particularly interested in

1. A shared filament supply for output tubes with fixed bias, individual bias supply, no hum pots. I have this in my 845 amp now(not monoblock, but separate chasis, ps & stereo front end) and it seems to be working fine. No audible hum and the sound is really good. The question is what improvement would I be likely to get with going to separate filament supplies and hum pots?

2. I just finished buiding a 300b amp. Again I used two chasis, ps and stereo front end. This time I used cathode bias and the shared filament supply for the 300b's uses a hum pot for each output tube. The amp sounds good, but there is a bit of hum left that is slightly audible at 8 feet or so. Can the shared filament supply for the 300b's be adding hum?
The other question that's nagging me is are the dual pots for a shared supply redundant? Again, What kind of improvement would I be likely to hear if I went to separate filaments supplies on the 300b's?
Thanks for the help!

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