[R-390] 17 MHz osc pull from AGC

[Flowertime01 at wmconnect.com]

Conard, WS4S,

Roy offered up some of the best things to try first.

You may be dealing with an old age problem here. Do the stuff Roy suggest 
first it easy, painless and most likely to fix the problem. 

I was thinking you may have a bad wire in the harness or a contact problem in 
the RF deck connector. Not a real open but enough to get you a voltage drop. 
My though was that as AGC voltage goes down (more AGC) the IF stages get cut 
off. The IF stages and the first crystal ocs share the RF IF B+ line. Plug 108 
pin K at the RF deck. As AGC changes tube gains, the B+ line voltage may be 
changing.

You may try a visual inspection on the back side of Plug 108 for frayed 
wires. The other end of that is the RF IF B+ fuse. A bad fuse could be getting you 
or poor connection in the fuse holder. 

You should also go the other way and try to look into plug P112 at the IF 
deck.

After this you could try a tube extender into the osc tube and see if you can 
watch the B+ shift as the AGC is built-up with a strong incoming signal.

You may have to pull the RF deck and do a real visual for a poor connection.
It may or may not be on the B+ line. It could be in the cathode circuit or in 
the screen circuit for the Osc tube. It could also be in the grid and the 
crystal can socket. 

In MGC you just hold the AGC line flat and thus do not shift the current 
operating points of the tubes. Signals run through the tubes and current varies 
but not to the extent the AGC shifts the operating points of the tubes. You are 
seeing a 17,000 to 1 shift on the Osc. The amount of B+ shift you see at the 
tube may well be under a volt. 

We have seen cold solder in the IF cans. You could have a cold solder joint 
in T207. Not an easy place to inspect but it can be done.

Good Luck with this one. Let us know what you find.

Roger KC6TRu