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Old 15th December 2010, 03:56 PM   #1
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Default Eico HF-89a question

Eico HF-89A question. Does someone have a schematic of the Eico HF-89a? My specific need is to know the value and location the low value capacitor that is attatched to the grid of V 2 and V 3. What is the location of the other end of this capacitor and the value?
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Old 15th December 2010, 04:06 PM   #2
SY is offline SY  United States
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0.25 microfarad/400V. You can use 0.33u, which will probably be easier to source. It goes between grid and ground.
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Old 15th December 2010, 04:19 PM   #3
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Quote:
Originally Posted by SY View Post
0.25 microfarad/400V. You can use 0.33u, which will probably be easier to source. It goes between grid and ground.
Solen makes a .27uF 630VDC for less than $2 each, one of the few actual .27uF caps out there and good for Mcintosh rebuilds too.
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Old 15th December 2010, 04:51 PM   #4
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There ya go!
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Old 15th December 2010, 05:43 PM   #5
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Default I should have been more clear. Sorry

Tubes V 2 and V3 are a dual tube - 6SN7. I am asking about the grid for the first tube - pin #1.
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Old 15th December 2010, 05:47 PM   #6
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Right. Pin 1 is bypassed to ground via that 0.25uF cap. Pin 1 is also connected to pin 4 via a 1M resistor.

V2 is Channel 1, V3 is channel 2. The other sections of those tubes (grid pin 4) are direct coupled to the input tube plate.
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Old 15th December 2010, 06:08 PM   #7
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Default Yes, but ----

Sorry, I am not asking about the 0.25 mf capacitor.
The capacitor I am asking about is a change brought
about when EICO changed vendors of the output
transformer. The HF-87 and first version of the HF-89
had a 750uuf placed across one half of the transformer
primary to deal with phase shift in the transformer. This
capacitor was replaced in the HF-89a. According to
old posts in the EICO Yahoo group. The new "fix" was
a "low value capacitor at the input of the 6SN7. The
amp I recently purchased does not have this capacitor
but I think I can see where it was cut off of pins 1
of each 6SN7. If someone has a 89A schematic, I
need to know the value and location of this capacitor.
Again, I am not asking about the 0.25 mf capacitor you
describe. I feel the cap. would somehow be connected
to pin four or five of V4 and V5. Thanks for your help.
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