42-1008 code 121 - Printable Version
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RE: 42-1008 code 121 - rperry - 01-13-2019
unfortunately not
RE: 42-1008 code 121 - rperry - 01-13-2019
I'm not entirely sure of the state of the tubes, I have a knight 600b tube tester but it doesn't list any of these tubes on the scroll
RE: 42-1008 code 121 - Radioroslyn - 01-13-2019
Good time to find one. Doesn't have to be anything fancy but it allow us to inject a signal and hear what stages are working. You can go thru and measure the pin voltages on all the tubes (5Y4 is ok) and see if there are any anomalies.
RE: 42-1008 code 121 - rperry - 01-13-2019
I'll see about acquiring one, and in the meantime i'll test and record pin voltages for each tube. As you can tell I'm new to radio's and I really appreciate the help you given me.
RE: 42-1008 code 121 - rperry - 01-13-2019
Ive got a heathkit sg-8 on the way
RE: 42-1008 code 121 - rperry - 01-14-2019
What kind of voltage should i be seeing out of the output transformer?
RE: 42-1008 code 121 - Radioroslyn - 01-14-2019
THe simple way to check the voltages at the transformer is to measure the plate pin of the output tube (on the 41's it's pin 2) So measure the voltage from pin 2 to the chassis. On both tubes should see abt 250vdc. Then measure the voltage on the screen grids (pin 3) should see about the same. One of the screen grids is going to be a bit lower in voltage as it has a 3,000 ohm resistor in series with the hv source.
RE: 42-1008 code 121 - rperry - 01-14-2019
nothing on those and the center tap is dead also... Looks like I'm back in the same boat. Do you know of a new tx i can get for this?
RE: 42-1008 code 121 - Radioroslyn - 01-14-2019
To be clear I'm speaking of the output transformer.
If the power transformer was bad (now) you wouldn't have 600vac from pin 3 to pin 5 on the 5Y4.
RE: 42-1008 code 121 - rperry - 01-14-2019
Power transformer:
3 and 5 (yellow)=637 ac volts
7 and 8(blue)=370 dc volts
on the 5Y4
Between black and black coming off the PT 6.5 volts ac
yellow-green center tap= o volts to chassis
Output transformer:
0 volts VDC from pin 2 on 41 tube to chassis
RE: 42-1008 code 121 - Radioroslyn - 01-14-2019
And pin 3 of the 41 tubes??
RE: 42-1008 code 121 - rperry - 01-15-2019
I got high tech and set up a thermal imaging camera on the chassis as I slowly wound up the variac, and found the #77 resistor on the far left side was what was getting hot and smoking.
RE: 42-1008 code 121 - rperry - 01-18-2019
I found 2- 470k resistors that where out of spec by a little over 20% that go to the bias resistor, I'm hoping that is my issue. What wattage resistor should those be replaced with? I don't see a rating on the schematic. 2 watt?
RE: 42-1008 code 121 - rperry - 01-20-2019
To follow up on this post, There was a short in the field transformer wires, and a resistor that was not connected. Set is now receiving. Thank you Terry!
-rperry