[R-390] Re: Image Problem

[SHELLY199 at aol.com]

Tony,

When you measured the  voltages below what was the gen input voltage?

Voltages are

With  no AGC applied:
Plate 201v
screen 178v
cathode 2.1v
grid  -.5v

With AGC applied:
Plate 215v
screen 201v
cathode  .22v
grid -4.2v


The agc, with the Langford mod, should be  about:

10 Uv rf input = -4.36 Vdc
100Uv rf input = 6.66
1000 Uv rf  input = 8.53

I don't know if this will help, but you are talking some  very big rf input 
voltages (20mv). 

I also had a problem with the Ist rf  amp not responding to the AGC voltage 
once.   Tube tested good and the  agc voltage was there.  Was fixed with 
another rf amp tube.  That took  a lot of work. 

By the way, if you use In914 or In4148 diodes in that  Langford mod I've 
found that one of the diodes will fail.  I use  1n5060.  I think it's breakdown 
when the AGC switch is turned from slow to  medium. This has happened in at 
least 5 IF decks.

Rich WD2Q  




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