[Amps] SB-220 amp help

[Carl]

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 at contesting.com>
To: <amps at 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 at 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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