In Reply to: Re: Hum pot in DHT preamp ??? posted by Thomas Mayer on November 1, 2001 at 07:45:25:
lets assume more traditional R/C coupling....the filamnet has a 7.5V dc potential across it.... now tie one side to ground (through the RC) and build two different supplies a +7.5V one and a -7.5V one the two different filament supplies will considerably change where the tube biases up, and for the same operating point two different bias resistors will be needed...i think the negative supply will require a smaller bias resistor for the same current... the down side is grid current will start to flow when the grid hits -7.5V rather than zero...this is a problem in output tubes, but in drivers and such were we tend to keep well clear of the 0 bias point... maybe this is a place to make a small gain???
in other words with the -7.5V supply when one 1/2 of the filament is at -7.5V the other half is at zero and some grid current will start to flow. but with the +7.5V supply when one 1/2 of the filament hits 0 the other 1/2 is still at -7.5V so the grid current will start flowing with a difference of bias of 7.5V
is this making sense???
dave
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Follow Ups
- Re: Hum pot in DHT preamp ??? - dave slagle 09:35:52 11/01/01 (9)
- Re: Hum pot in DHT preamp ??? - Thomas Mayer 09:49:48 11/01/01 (8)
- Re: Hum pot in DHT preamp ??? - dave slagle 14:09:25 11/01/01 (7)
- Re: Hum pot in DHT preamp ??? - Thomas Mayer 17:25:18 11/01/01 (6)
- Re: Hum pot in DHT preamp ??? - dave slagle 08:44:35 11/02/01 (5)
- Re: Hum pot in DHT preamp ??? - Thomas Mayer 12:24:45 11/03/01 (1)
- Re: Hum pot in DHT preamp ??? - dave slagle 07:37:03 11/06/01 (0)
- Re: Hum pot in DHT preamp ??? - larry moore 10:03:58 11/02/01 (2)
- Re: Hum pot in DHT preamp ??? - Thomas Mayer 12:21:44 11/03/01 (1)
- Inspiration - J Epstein 13:09:24 11/03/01 (0)