[R-390] Yet another question... sigh...

[ToddRoberts2001 at aol.com]

In a message dated 9/18/2006 9:49:50 AM Eastern Standard Time, 
n4buq at knology.net writes:
Still mulling this over.  Injecting a 0.1V modulated 455kc signal at the 
plate of the detector (V506) isn't giving any output.  If I inject 0.15V 
audio at the grid of V507, I get the expected results so the table says the 
problem is in the detector circuit.

What I can't figure out is the radio does play -- perhaps not to 
specification, but it does play so I'm curious how the problem could be in 
the detector.

Not sure where to go from here.  There's very little componentry around the 
detector (and I'm running a NOS tube there just in case) so it should be 
easy to spot if anything's amiss there.

Weird.

Barry - N4BUQ

What exactly is the problem with the radio? Is it weak or distorted audio? I 
have seen the .1uF coupling cap C531 between V506 and V507 go bad. That could 
be why you get output when you inject an audio signal into the grid of V507 
but no output when you inject an RF signal into the plate of V506. Two other 
troublemakers around V507 are the small mica bypass caps C532 100pf and C537 
180pf. Those seem to be more prone than others to short or get leaky. But first I 
would try replacing C531 and see what happens. Also you might check resistors 
R526 and R527.  73 Todd WD4NGG