[R-390] AGC action on oscillator frequencies, cures?

[Flowertime01 at wmconnect.com]

Tim,

I have on sure cures. One problem is current limiting through the deck 
connectors. But once you deox them and check the back side for good solder to ensure 
good cross section for current conduction there is little you can do to 
enhance the current path in these elements. But if you have real bad pull, it could 
be worth your time to do an inspection and repair if necessary. 

These receivers did shift. But most operators though of them as very stable. 
Like they never had an opportunity to work with a better receiver as one had 
not been built back then. But if yours shifts enough to be noticeable you 
likely have a problem worth investigating. It sure would be nice if you have two 
receivers to set up side by side to determine if one shifted more than the 
other. Many trouble calls went down as no trouble found when we did side by side 
test of two receiver and found the difference to be antenna choice or just a bad 
ear night.

Fifty plus years of age makes a difference.

A guy in San Francisco area makes solid state replacements for tubes. He 
could make you up some solid state tubes.

You use the screen voltage pin into a zener diode regulated voltage. The 
cathode becomes the FET base. You decouple the cathode resistor back to ground by 
selecting the correct filament pin. You add to the cathode resistor to get the 
grid bias to fit the base bias voltage you need. A resistor into the screen 
zener regulated voltage becomes the cathode or drain load. A cap couples the 
signal back to the plate and the plate voltage is ignored.

He puts the stuff in a nice sleeve with a 7 pin socket. Noise is lower. You 
can reengineer the guts for more or less gain. The filament voltage heat goes 
away. You never have to check the tube again.

I have a nice 6DC6 in one of my R390/A. The noise of the RF tube is not the 
limiting factor in getting a better signal to noise ratio out of my receiver. 
So until I get to the source of my noise problem, more solid state tubes are 
not of value to me. I like my one solid state replacement. It is canned. I know 
not what is inside. It performs a little better than any 6DC6 I own. I do not 
think it performs better any 6DC6 that I could own. I have not measured it to 
be sure. 

So there are things that can be done. 

Roger AI4NI