The HV metering resistors may have opened up. For the power its common for
D-17 and C-54 to develop leakage and the pot to open. Id also check R-24 and
25 as carbon resistors tend to increase in value over time and especially
with RF.
Carl
KM1H
----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: <amps@contesting.com>
Sent: Wednesday, April 06, 2011 8:43 AM
Subject: Re: [Amps] SB-220 amp help
> My SB-220 has been an absolute joy since I bought it a decade ago, at
> which point it was already about 25 years old, but this message raised a
> question. In CW contest service, I have always used the SSB position,
> and it puts out >1200 watts on every band but 10M. No major component
> failures, though it did melt the solder in the 3-500 filament pins until
> I swapped the socket clips and polished the pins to improve contact.
>
> Only one issue. For some reason, the high voltage and relative power
> positions on the multimeter quit years ago, while the grid current still
> works. I didn't really need them, but it would be nice to have
> everything working. I'm assuming a common cause, but I'll be darned if
> I can see a component or components that would cause this, other than
> the switch itself. Can anyone point me in the right direction?
>
> 73, Pete N4ZR
>
> The World Contest Station Database, updated daily at
> www.conteststations.com
> The Reverse Beacon Network at http://reversebeacon.net, blog at
> reversebeacon.blogspot.com,
> spots at telnet.reversebeacon.net, port 7000
>
>
>
> On 4/6/2011 8:14 AM, Gudguyham@aol.com wrote:
>> GM guys, since we are beating the hell out of the Heathkit amplifier
>> these
>> past few days, I want to offer some help to you who are new to the amp.
>> Here is an occasional problem that comes up that can frustrate you. Does
>> your sensitivity meter not work right? Does it only give you a reading a
>> one
>> point is its rotation? Then when it does, the meter slams against the
>> pin? SO you say oops, my sensitivity pot is bad, and you replace it and
>> as
>> soon as you put power through your new pot it goes south again? The
>> problem
>> is leakage in the 1N191 detector diode. You need to change the diode or
>> else you will burn up any number of pots you replace. The 1N191 is not
>> made
>> anymore and it looks like 1 1N60 is a good replacement. This tip might
>> save
>> you a lot of aggravation. I am assuming what happens is that the diode
>> leaks RF and it burns the pot as I have dissected several pots and found
>> the
>> same "burn" on all that were bad. Happy motoring.
>> _______________________________________________
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>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>
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