Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Spent an hour going through the 51S-1 Schematic to get myself familiar with the layout again.. Interesting is the 25.2 Volts AC used to feed all the Filaments in the 6 volt tubes.. You basically have 4 tubes in series, with several stages divided with dropping resistors and filter capacitors.. I did get some feedback early last year that someone who had the same issue found a cold soldering connection/Bad Capacitor on one of the filament of a tube..

Not sure Electrically why Collins did this type of Filament set up, but it must have been for a very sound engineering reason..

 

This is a link to a short 1 minute Video of the filament circuit and 25.2 Volt AC power transformer. If your familiar as to why this was done this way, it would be appreciated to share your knowledge.. The KWM-2A has a somewhat similar setup for some of its tubes..

 

https://www.youtube.com/watch?v=x4S52RDGNgM

 

Robert WA6PHN

 

From: Amateur-repairs@groups.io [mailto:Amateur-repairs@groups.io] On Behalf Of Gary WB6OGD
Sent: Friday, January 19, 2024 8:58 AM
To: Amateur-repairs@groups.io
Subject: Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

 

Robert,
Good advice.
I am no expert but I believe you can't rely too heavily on any tube tester.  The actual circuit where the tube goes is the best tester.

I downloaded the 51s1 manual just to have a look.  The BFO is one tube.  I would try another, there are probably many types that could substitute
there if you don't have a good spare.  I am thinking it maybe has a filament to cathode short or leakage of some kind that lets the AC filament signal onto
the BFO signal.  But just a guess.
73,
Gary
WB6OGD