[Amps] more sb220 questions

[John Adkins]

Bob--
Thanks for the suggestion.  I've already removed the wiring to/from the ext xformer, and I'll
remove the connectors in the next couple of days.  I'm going to leave the Amperite relay in place,
since it does no harm.

I'm also going to remove at least two of the sides of the socket shield so that cooling can be
improved.  I plan to leave the other two sides because removing the feedthru caps is such a pain. 
If you think it's a mistake to leave any of it, let me know.

15 or so years ago, Robert Kozlarek, WA2SQQ, compiled "The Complete Book of SB-220 Mods."  It
looks like the previous owner of this amplifier make most of the modifications listed in the
compendium.

Weep.

Thanks

John
w4kv

--- Bob Alexander <realex at flash.net> wrote:

> Hi John,
> Since the mid 70s when I was a tech at Heathkit, I have rebuilt/restored
> around 30 SB220s.
> Im sorry to say it but I cannot think of a good reason for any of the
> changes I can see in
> the pictures.
> It looks like two of the three grid pins on each socket may have been
> directly grounded (thats good) but the third lead is above ground with a 1K
> resistor.  This may be an attempt at changing the grid metering circuitry.
> That may explain why you see no grid current.
> It is a mystery to me why anyone would shield the tube sockets and kill the
> cooling scheme for the tubes.
> 
> My suggestion would be to remove everything that is not original and
> completely restore it.
> 
> 
> Good luck
> 73, Bob, W5AH
> 
> 
> 


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