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Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time. |
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Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time. |
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In Reply to: RE: Both channels equally sibilant? posted by Akolegov88 on August 12, 2019 at 11:04:42:
These HF-81 amps are "survivors" in the truest sense. I still know some folks using original tubes and coupling caps, including the ceramic caps, not to mention the original power supply caps !
Of course, some units were not so lucky through the years and some have had their power tranny replaced. Original Eico wiring uses the dual rectifiers as "independent" for (only) each half of the B+ (HV) high voltage winding. This can cause some (serious) unbalancing when one 6CA4/EZ81 stays strong and the other one gets weak.
That could actually have been the cause of the blown power trannies. A retrofit wiring change for each EZ/81/6CA4 to work on both halves of the winding will cure the possible troubles. This way, with the diode sections "in parallel between the tubes," when and if one EZ81 tube gets weak, the voltage will only sag on crescendo peaks, causing slight distortion, but retaining balance within the tranny.
HF-81s are among the first three stereo integrated amps, introduced in 1958. Early versions come with long plate Mullard 12AX7s ! The phono stage is actually top notch. My fave retro-resto for the HF-81 is making the Mic and Tape (Head) inputs into "extra" phono inputs. I add an EQ network for the Mic input and I change the Tape EQ into switchable phono EQ networks. With the HF-81 preamp section being very similar to the HF-85 preamp, then combined with a sweet, detailed sounding stereo PP EL84 amp on one chassis, my HF-81 will still be a keeper....
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Follow Ups
- I m so glad it's alive again.... - Interstage Tranny 08/13/1916:09:26 08/13/19 (1)
- RE: I m so glad it's alive again.... - Akolegov88 16:28:42 08/13/19 (0)
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