A string of 2.5 amp silicon rectifiers, with any PIV rating, with a .01uF
cap across the string, can be substituted for the zener diode. I added
diodes into the string until the idling current for the pair of triodes was
about 160 milliamps. This should be about 5 to 7 diodes.
Higher idling current up to about 200 milliamps, should also provide good
linearity, run the triodes somewhat hotter, and be somewhat easier to drive
to full output.
The anode side of the silicon rectifier string should be inserted into the
circuit where the old zener diode cathode was formerly connected. The
silicon rectifier is forward conducting, whereas the zener diode is reverse
conducting, hence the change.
73 and Happy DXing,
Mike
W2AJI
----- Original Message -----
From: "Jay Musikar" <af2c@yahoo.com>
To: <Amps@contesting.com>
Sent: Wednesday, November 01, 2006 4:25 PM
Subject: [Amps] Heath SB220 Zener Replacement
> I am currently restoring a SB220 and the 1N3996 Zener
> (ZD1)has been physically removed from the amp.
>
> It is apparent that the previous owner was not neatest
> individual in the world, so I have my work cut out for
> me.
>
> It is my understanding that this Zener can either be
> replaced with another one or with a series of silicon
> diodes in lieu of a another 1N3996.
>
> 1. What is the configuration of the silicon diode
> substitution? As I recall it was done by substituting
> five (5) diodes in series in place of the Zener.
>
> 2. Do any of you have a schematic for the mod...If so
> please scan it and send it via email to:
>
> af2c@arrl.net
>
> Thanks in advance es 73,
>
> Jay/AF2C
>
>
>
>
>
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