[SignalOne] Transmit Level

[jerry]

Hello!

    My CX7A is transmitting well on all bands except 10M.  However, the 
transmit chain seems to have low gain.  For decent output, I have to 
turn the OUTPUT knob all the way CW.  According to the manual, I 
shouldn't have to turn it
past 9 O'Clock!

    The list of transmitter voltages in the manual is confusing to me.  
The exact conditions of measurement.

   SO:  Here I have the radio on 40M.  TUNE mode.  100W output.  Probing 
at the input to the RF board ( Pin 267 ).
The OUTPUT control is slightly past its midpoint.  Seeing 760mV 
peak-to-peak.

   Can anybody tell me:  is the low gain BEFORE that input, or AFTER it?

   OK, I think I answered my own question.  Regardless of conditions - 
the table says that when the voltage at the
RF board output is 40V p-p ( see some clipping at that level ), the 
input voltage at pin 267 should be 180mVp-p.
Whereas it is ACTUALLY 940mV p-p.  So something ON THE RF BOARD is not 
performing up to spec.   The board as a whole
should have a voltage gain of 222 whereas it actually has a voltage gain 
of 42.

   Now to do the same exercise inside the board.  I really hope it's the 
CA3028A;  I have two of those here.  The big
transistors are pretty much unobtainium.  But it's not necessarily a 
semiconductor;  this thing is full of carbon comp
resistors, and I have already found two that have drifted up in value.

   For this work, I really love my Hantek 2D72 handheld oscilloscope.  It 
has measurement functions that let me just
read voltages off a tiny numeric display, instead saying "Lemme see:  
We're set at 100mV per division, and we have a 10x probe, and the signal 
starts HERE and ends THERE and...let's nudge it down just a bit and look 
at the top..."

                         - Jerry, KF6VB