"Ernie" wrote in message
...
Thanks for your thoughts Tim.

No, there's not means to switch the AVC off. The TR-4 has
a scheme whereby
signal is taken off an IF transformer and applied to an
"AVC amplifier" that feeds it
across a plate resistor that develops current which then
varies the voltage to the grids of the
preceding IF amplifiers and detector. As the voltage is
varied, the output from their plates
increases or decreases the gain, depending on whether the
signal is stronger
or weaker which provides the AVC control. The S-meter
comes off of the same
system. My S-meter will not adjust any lower than "S6"
with the S-meter zero
pot, so I am guessing that there is too much current being
drawn somewhere
resulting in too much grid bias which provides too much
AVC action, which is
the same thing that rotating the RF GAIN control down
does.

My problem is that I hear almost no "receiver hiss" even
with the volume
control all the way up. I do hear signals, but they are
very weak and
rotating the IF and RF transformer trimmers has an effect
on the amount of
signal from my sig gen that I get. But the overall volume
is way, way down.

In addition, if I inject a 9 MHz signal to the grid of the
1st IF transformer, I get lots of
signal from the plate. But if I inject a signal to the
grid of the 2nd IF transformer, the signal level from its
plate is very low. Ordinarily that would mean the tube is
defective, but it's not. I've swapped two NOS tubes (that
all test well on a reliable professional tube tester).I've
checked that IF amp's bypass caps and load resistors.
Nothing.

So my focus is still on the AVC.

OK I didn't see this post when I replied. The up-scale
reading of the S meter does suggest something is wrong with
the bias. Have you checked the voltages around V13a? It is
also worth swapping V13 in case you have a gassy one. My
other suggestions don't apply other than getting the disc I
mentioned.



--
Richard Knoppow
Los Angeles
WB6KBL