Request for EICO HF-20 experiences and ideas

Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

I picked up a pair of HF-20s on eBay for $140 before the current inflation in price for that company's products. (I recently saw an HF-81 going for over $500; I paid $110 for one about five years ago.) The units are in perfect but totally original condition, so they need a thorough going-over (replacement of electrolytics, coupling caps and out-of-spec carbon comp resistors) before they can be used. They'll as mono amps only, with everything bypassed except for the volume control, which will be replaced with a switched attenuator for balance.

The original unit had some very impressive specs for the time, even compared to modern tube amps. The schematic shows a fairly typical Williamson circuit without any unusual design flourishes that I can see. I know people here must have had experience with this unit, and ideas on what to upgrade. The PS lacks any inductance, so an obvious step will be to replace the first resistor with a choke of appropriate DCR; I'd appreciate suggestions as to the appropriate inductance to use here. Any other ideas would be appreciated as well. TIA.

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Topic - Request for EICO HF-20 experiences and ideas - tomsyl1 01:43:23 06/12/08 (7)

Generalization for rebuilding vintage PP amps - Neff 06:07:12 06/15/08 (0)

RE: Request for EICO HF-20 experiences and ideas - Caucasian Blackplate 08:52:50 06/12/08 (0)

RE: Request for EICO HF-20 experiences and ideas - Door Nail 08:33:05 06/12/08 (0)

RE: Request for EICO HF-20 experiences and ideas - Scholl 03:48:15 06/12/08 (3)

Thanks everyone for the ideas - tomsyl1 00:06:20 06/13/08 (2)

RE: Thanks everyone for the ideas - maynardg 14:09:06 06/13/08 (1)

Neat - thanks! - tomsyl1 04:55:48 06/15/08 (0)

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