Hi chapsI've recently been intrigued by the concept of using a very low value of cathode resistor for biasing. Such a low value doesn't need bypassing. The current for the resistor is obtained from a secondary supply. Here's a basic description from the tnt review of the European Triode Festival 2004 where it won a shootout of biasing methods:
"Manfred Huber (Germany) elaborated on the various methods of providing bias voltage to a triode. In the following shootout the audience rated LOW-R bias best (that is using a low value resistor in the cathode and having additional current from an auxiliary supply - typically the dc heater supply - flowing to it, such that the desired bias would settle), then surprisingly Miss Piggy got a second price (capacitor bypassed cathode resistor), all the other methods (battery in cathode, battery in grid, LED bias, fixed voltage for grid and cathode to ground, non-bypassed cathode resistor) proved to have more or less uncomfortable sounding shortcomings."
A basic schematic is on the tnt website at the enclosed URL if you are interested.
I built a circuit (just like the one shown on the tnt site) today to see how it works. From what I can tell, it's just basically a voltage divider (between R1 and Rk). Maximum cathode voltage is limited to the secondary voltage supply (eg. DC heater supply). Isn't this just the same as using fixed bias, but applied to the cathode instead of the grid? Is it really a good idea to share the heater voltage with the cathode?
Perhaps I'm doing it wrong? Anyone else out there used this?
Cheers. Doug
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Topic - Low cathode resistor bias - Doug Flynn 21:47:01 07/16/05 (43)
- Re: Low cathode resistor bias - J Epstein 05:29:13 07/18/05 (0)
- Re: Low cathode resistor bias - Ray Moth 23:00:48 07/17/05 (0)
- Another way to look at this - BBeck 06:31:16 07/17/05 (0)
- Re: Low cathode resistor bias - MIchael Samra 01:19:10 07/17/05 (29)
- Re: Low cathode resistor bias - Ray Moth 17:51:20 07/18/05 (7)
- "solely"? Nope. - Joelt 05:12:09 07/19/05 (6)
- Re: "solely"? Nope. - Ray Moth 06:30:21 07/19/05 (5)
- Re: "solely"? Nope. - Joelt 07:00:40 07/19/05 (4)
- Re: "solely"? Nope. - Ray Moth 19:56:39 07/20/05 (0)
- Have to disagree on this one - Triode_Kingdom 08:32:56 07/19/05 (2)
- Re: Have to disagree on this one - Joelt 08:43:07 07/19/05 (1)
- Not good enough - Triode_Kingdom 12:29:45 07/19/05 (0)
- Re: Low cathode resistor bias - jdarg 13:54:14 07/18/05 (12)
- Re: Low cathode resistor bias - MIchael Samra 10:32:39 07/19/05 (0)
- Re: Low cathode resistor bias - Joelt 05:09:02 07/19/05 (10)
- Re: Low cathode resistor bias - MIchael Samra 10:33:24 07/19/05 (0)
- 15.6 ohms was used.... - Russ57 07:09:31 07/19/05 (8)
- Re: 15.6 ohms was used.... - dave slagle 19:21:22 07/19/05 (0)
- Re: 15.6 ohms was used.... - Joelt 07:44:44 07/19/05 (6)
- Re: 15.6 ohms was used....The way its figured is - MIchael Samra 17:14:28 07/19/05 (0)
- Page 10, last two paragraphs, of the Dynaco 70 assembly instructions - Russ57 10:14:43 07/19/05 (3)
- Re: Page 10, last two paragraphs, of the Dynaco 70 assembly instructions - Kyle K 11:20:30 07/19/05 (2)
- And all intended to give a voltage of 1.56VDC(nt) - Russ57 12:17:45 07/19/05 (1)
- Bingo! (nt) - Kyle K 12:46:41 07/19/05 (0)
- Re: 15.6 ohms was used.... - Kyle K 10:09:51 07/19/05 (0)
- Not sure what you mean - Mark Kelly 18:39:52 07/17/05 (0)
- Dynaco: it's not "low cathode resistor bias". - Joelt 04:30:37 07/17/05 (6)
- IM - Triode_Kingdom 11:13:21 07/17/05 (5)
- Re: IM - Dave Cigna 14:07:09 07/17/05 (2)
- Re: IM - Homer Jay 15:41:45 07/17/05 (1)
- Well in that case...Nevermind. :) (nt) - Triode_Kingdom 23:56:30 07/17/05 (0)
- Re: IM - Joelt 12:53:53 07/17/05 (1)
- Re: IM, CMR - drlowmu 22:13:52 07/18/05 (0)
- Re: Low cathode resistor bias - Paul Barker 23:30:27 07/16/05 (9)
- Hot stuff! - Brian C. 10:50:02 07/17/05 (7)
- Re: Hot stuff! - Paul Barker 11:13:59 07/17/05 (6)
- Re: Hot stuff! - Brian C. 13:45:21 07/17/05 (5)
- Re: Hot stuff! - Paul Barker 23:29:37 07/17/05 (4)
- Yes, I remember... - Brian C. 03:04:16 07/18/05 (3)
- Re: Yes, I remember... - Paul Barker 04:14:37 07/18/05 (2)
- Re: Yes, I remember... - dave slagle 18:36:50 07/18/05 (1)
- Re: Yes, I remember... - Paul Barker 22:53:26 07/18/05 (0)
- Re: Low cathode resistor bias - Paul Barker 07:38:58 07/17/05 (0)