Upon turning set on (of coarse after warm up)
audio is very low. When I touch a probe from
my voltmeter to control grid of 75 tude, audio level
jumps to normal level. Almost like agc level
is turning the gain way down. I have tried to
monitor the agc voltage, but can't seam to
get a handle on this problem. Also,no apparent oscillation when probing with scope.
Any suggestions?
Thanks
John
Have you replaced caps in your radio? Even after replacing caps I have had radios act this way.
In some I have found bad contact with grid caps or tube pins. Try resoldering top cap of your 75. Resolder pins on 75 & 41 tubes.
Check for any rivets expected to carry ground from the chassis. They oxidize over time and make bad contact.
Norm
:Philco 25-39, tube line up 6a8, 78, 75, 41, 84.
:
:Upon turning set on (of coarse after warm up)
:audio is very low. When I touch a probe from
:my voltmeter to control grid of 75 tude, audio level
:jumps to normal level. Almost like agc level
:is turning the gain way down. I have tried to
:monitor the agc voltage, but can't seam to
:get a handle on this problem. Also,no apparent oscillation when probing with scope.
:Any suggestions?
:Thanks
:John
I had been thinking this problem
was in the RF section. (agc)
Seams as though it was the coupling cap between
the volume control pot and rest of the audio amps.
I replaced the cap and all has been well.
Thanks again.
John
:Hi John
:
: Have you replaced caps in your radio? Even after replacing caps I have had radios act this way.
:
: In some I have found bad contact with grid caps or tube pins. Try resoldering top cap of your 75. Resolder pins on 75 & 41 tubes.
:
: Check for any rivets expected to carry ground from the chassis. They oxidize over time and make bad contact.
:
:Norm
:
::Philco 25-39, tube line up 6a8, 78, 75, 41, 84.
::
::Upon turning set on (of coarse after warm up)
::audio is very low. When I touch a probe from
::my voltmeter to control grid of 75 tude, audio level
::jumps to normal level. Almost like agc level
::is turning the gain way down. I have tried to
::monitor the agc voltage, but can't seam to
::get a handle on this problem. Also,no apparent oscillation when probing with scope.
::Any suggestions?
::Thanks
::John