[R-390] Z-503

[Charles Steinmetz]

Ross wrote:

> Hi all, Pardon me for not shuffling through endless pages of R-390A info, but I need to know the value of the capacitor in Z-503.  I am having AGC problems and am coming to my wits end.

As I recall, C563 is typically around 82pF, though there is some 
variation.  Note that Z503 is a *low-Q* plate load for V508, so it's 
pretty non-critical.  Also check C543 (the V508 cathode bypass 
capacitor), C544 (the screen bypass capacitor), and the value of R541 
(the cathode resistor).

Of course, low gain anywhere in the IF section would produce similar 
symptoms.  Is there any specific reason, other than the previously 
defective (and now replaced) Z503, that you suspect Z503 and/or C563 now?

Have you been through the AGC troubleshooting procedure I have posted 
here several times (most recently on 10/6/2018)?

Best regards,

Charles