08-05-2019, 02:52 PM
Moving ahead I constructed an adapter from the 76 tube to a 6C4. That helped some and I gained a couple of hundred kc's lower now. To track it I've been using a Kenwood TS-440's receiver. Did note that the amplitude of the oscillator lowers before it dies, can watch on the receivers S meter.
Lowered the value of the 76's plate resistor down to 12K to see if I could get a little more gain and it did but just a little. I need more dissipation!
Next I measure the heater voltage at the socket and it was 5.6vac. Kinda low. Hooked up my variac and got the voltage up to 6.2v. This helped too.
Measured the cathode voltage and it seemed to be reasonable at abt 4v. Now the 77 mixer's cathode is connected thru a 1250mmfd cap to the 76's cathode. This how the oscillator signal is coupled from the oscillator to the mixer. The mixer cathode is 5k above ground so the voltage there should be somewhat higher. It wasn't it was fairly close to the voltage at the 76. Disconnected the 1250mmf cap and replaced it. Not much of a change.
Did note that when I was measuring the voltage at the 76 cathode the oscillator seemed to perk up and almost acted as it should. I'm thinking abt adding a gimmick cap to see if this will correct the original.
There is a light at the end of the tunnel and no train is coming at me.
Lowered the value of the 76's plate resistor down to 12K to see if I could get a little more gain and it did but just a little. I need more dissipation!
Next I measure the heater voltage at the socket and it was 5.6vac. Kinda low. Hooked up my variac and got the voltage up to 6.2v. This helped too.
Measured the cathode voltage and it seemed to be reasonable at abt 4v. Now the 77 mixer's cathode is connected thru a 1250mmfd cap to the 76's cathode. This how the oscillator signal is coupled from the oscillator to the mixer. The mixer cathode is 5k above ground so the voltage there should be somewhat higher. It wasn't it was fairly close to the voltage at the 76. Disconnected the 1250mmf cap and replaced it. Not much of a change.
Did note that when I was measuring the voltage at the 76 cathode the oscillator seemed to perk up and almost acted as it should. I'm thinking abt adding a gimmick cap to see if this will correct the original.
There is a light at the end of the tunnel and no train is coming at me.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
