Hi,

If you were operating the radios with the AGC off,
that would cause the blocking action at the higher gain settings
which you noted.

The S-40 radios are intended to be used with AGC switch "on" in A.M. mode.

AGC "off" is intended to be used only with the BFO on (for c.w. reception).
This is because the beat frequency oscillator would otherwise
be detected by the AGC circuit as if it was a very strong received
carrier, which would cause an unwanted constant reduction in the
receiver gain by AGC action during c.w. reception.

73,
Ed Knobloch



getSteven Burrows wrote:

What would cause a lack of AGC action? I was operating the radios with the
AVC off when I noted the apparent RF gain saturation. Would a lack of AGC
be a result of the radios being misalligned, or is it symptomatic of a
component failure?
"Edward Knobloch" wrote in message
news:kcJZe.9419$gi4.6305@trndny04...

Hi,

It sounds like you no longer have automatic gain control (AGC)action.
The AGC circuit should provide a negative voltage to the grids of the IF
amplifier tubes, to reduce their gain with strong signals.
Lack of AGC would lead to "blocking" which is as you describe.

73,
Ed Knobloch



Steven Burrows wrote:
snip

Recently, I got both chassis ready to try out. They both worked ok, but
I noticed a new problem on both radios that I didn't see on the first
restoration (new caps only). When I turn the RF gain pot up beyond
approximately 66% of full rotation clockwise, the radio sensitivity drops
significantly and no stations or normal static can be heard. When I back
off on the gain control, the radio returns to normal. I am guessing that
this sympton (observed on bot radios) is from RF amplifier overload. Is
this behavior normal for a tube radio, and is there a fix? These are the
first boatanchors that I have ever tried to work on, so all of this is a
new experience to me. In all cases, I had the radio hooked up to a 100
ft. random longwire antenna.

If this behaviour is a symptom on a goof-up on my part in rewiring the
sets, I would appreciate some advice on how to fix the problem.

Steve Burrows