[Gonset] More G-76 Update

[W5HTW@att.net]

G76 update and general comments

Got my G76 aligned.  Hot receiver, except on 15 meters where it is only 
average.  Still puts out 65 watts on AM into a dummy load, which seems high. I 
would guess that figure should be about 45 watts, but I see no ill effects so 
far.   

Anyone intimately familiar with various versions or mods?  Meter only reading 
about 100 ma on transmit, so it is obviously wrong.  Plate voltage under load 
is 590, with 65 watts output.   A guess, based on a maximum of probably 55 
percent efficiency, is that the final is running about 120 watts input, which 
is high. That means the meter should be indicating nearly 200 ma instead of 
150, but is actually showing 100-110.  In fact, on LOW power, it barely dips at 
zero.  The meter itself is fine as it works correctly on receive.  

According to schematic, there are two parallel resistors in the 12AQ5 clamp 
tube plate, each is 47K, 2 watt.  On mine that was replaced with a single 
5-watt resitor.  The color bands have faded and are unreadable, but looks like 
the third color could have been brown, which would not make sense.  It actually 
measures 8500 ohms when removed from the circuit.  I'm going to replace it with 
a 5-watt value nearer 25K.  This is off pin 5 of the OB2, which I noted does 
not 'fire' on transmit.  

Relays were removed and cleaned and seem to be working very well.  Had to 
create a slug for the L1 VFO coil, and that appears successful for the moment. 
 
No crystal so have not checked the unit on six meters.  

Made a local (7 miles or so) contact on 75 meter AM and noted it was a solid AM 
signal but there was some hum on the carrier.  With no way to measure 
modulation, I think I had the gain too high.  Saw a downward deflection in 
power output with modulation.  Reduced gain to about mid point, using a 
Shure 444 wired for high impedance, but have not since checked the rig on the 
air.  Monitoring locally in the shack, the hum still seems to be there but less 
noticeable.  Oddly it is audio hum like an ungrounded microphone input, rather 
than 60 cycle hum.  Turning mike gain to zero removes the hum, but it is there 
whether or not the microphone is plugged in.  May just be too much gain in the 
mic amplifier, due to changed values over the years.  No hum on receive. 


The old rig is slowly breathing again.  

Comments regarding the radio are welcome.

73
Ed