SB220

[Stu Lyon]

The 51-27 was used by Heath all over the place and was rated at 600
PIV/500mA. A cheap modern replacement is the 1N4007 which is rated at
1000PIV/1A and cost less than $.10 each. Mouser has them for four cents each
in qtys of 25. Twenty-five diodes for $1.
http://www.mouser.com/catalog/616/281.pdf

Although you could take advantage of the higher voltage and use less diodes
in series, it's probably safer to just replace the diodes 1 for 1.

However, I'll bet it's not the diodes -- more likely the high voltage
metering circuit. Heath always over-stressed the scaling resistors in the
high voltage metering. It would be interesting to measure the HV with a VTVM
with a high-voltage probe. If you had such a thing.

73, Stu W6CUX

----- Original Message -----
From: "Alex Wa4Ak" <LAWALEXKAPLAN at AOL.COM>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Thursday, December 25, 2003 11:30 AM
Subject: SB220


> I have an SB220 in near mint condition.  My problem is that when testing
> according to the manual, the high voltage readings are a bit low, perhaps
400
> volts low.  I think it may be the silicon diode stack in the high voltage
power
> supply, but the manual and schematic only refers to them as silicon diodes
with
> a Heath in-house part number of 57-27.  Does anyone know a good modern
> substitute for these and a source for them?  Any assistance would be
appreciated.
> Alex Kaplan, WA4AK
> lawalexkaplan at aol.com
>
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