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In Reply to: RE: Rebuilding an Eico HF-87 and have some questions and concerns posted by Ray Moth on December 14, 2008 at 22:43:35:
> > > That looks like a contradiction of your first statement and it doesn't match the schematic I've seen.In the schematic contained in the original HF-87 manual (which I will scan and post later today), there are two channels shown. The cathodes of one channel have a 235 ohm cathode resistor while the other channel has a 165 and a 54 in series. It's pretty bizarre (to my eyes anyway).
> > > Your best solution, if you don't want to change to individually adjustable fixed bias, is to use separate cathode resistors of 2x the ohmic value of the original shared resistor, say 270 ohms each. Each cathode resistor should be bypassed by its own individual cap, say 220uF. This arrangement will be largely self-balancing, so long as your EL34s are not too mismatched.
That sounds like a winner to me. But shouldn't the resistors be 470 ohm if the original shared resistor was 235? The original arrangement uses a 50uF bypass cap, FWIW.
I'll post the original schematic here later today. It shows all circuitry, including the PS, of course.
Thanks,
Adam
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Follow Ups
- RE: Rebuilding an Eico HF-87 and have some questions and concerns - LowRedMoon 12/14/0823:06:22 12/14/08 (2)
- RE: Rebuilding an Eico HF-87 and have some questions and concerns - Ray Moth 06:55:41 12/15/08 (0)
- RE: Rebuilding an Eico HF-87 and have some questions and concerns - lovetube 03:47:17 12/15/08 (0)
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