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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: Switching from fixed to cathode bias posted by DAK on March 30, 2014 at 16:15:05:
No you don't need to change the front end.
What ever was driving the 4 x fixed bias EL34 will drive 4 x Cathode biased EL34 just as well (or better).
The max Rg1 value on the EL34 will be relaxed compared to the fixed bias value. There MAY be some opportunity to relax the loading on the front end by increasing the Rg1 values.
You also won't need to change power supplies etc. The EL34 will operate just fine with the new Vak = B+ less bias volts. Some might scoff BUT I can tell you from Guitar Amp experience that cathode biased EL34 at the lower Vak (and lower screen to cathode voltage)sound more "relaxed" and "unstressed".
Do use separate cathode bias resistors for each EL34 tube, each with their own bypass caps. Spend a little extra on good bypass caps.
Cheers,
Ian
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Follow Ups
- RE: Switching from fixed to cathode bias - Gingertube 20:03:30 03/30/14 (4)
- RE: Switching from fixed to cathode bias - Paul Joppa 14:19:43 03/31/14 (0)
- RE: Switching from fixed to cathode bias - DAK 10:57:57 03/31/14 (1)
- RE: Switching from fixed to cathode bias - Gingertube 15:10:01 03/31/14 (0)
- Best answer !!! - drlowmu 22:36:03 03/30/14 (0)
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