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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: RE: EICO HF-89 restoration posted by Jim Doyle on August 29, 2010 at 18:41:06:
"replace the 18K resistors on the 6SN7 LTP with a self-biased CCS. Huge mega improvement - that is not only easy, but cheap. Second, I might consider throwing in a small choke to cleanup the B+ to the 12AX7 plates (Point X in the PSU diagram"
If you're going to give the LTP a CCS tail, which is an excellent idea, then you need also to make the plate load resistors of the 6SN7, R11 and R13, equal and precisely matched.
I agree with the idea of a choke to improve B+ for the 12AX7 stage, but I would also be inclined to use another choke straight after the voltage doubler caps and their 100k bleeder resistors (i.e. to feed the junction of R45 and R46), to help clean up the spiky B+ coming off the doubler. Although the PP amp stages do have good PSRR, you still don't want all that noise spreading itself around the PS.
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- RE: EICO HF-89 restoration - Ray Moth 15:26:31 09/01/10 (0)
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