I am having difficulty getting any reception after recapping and replacing out of spec resistors. While I can see the expected voltages on the schematic for some tubes, others, particularly one of the 2 XXL's shows none. Should I assume they should both be the same? I have attached a summary of the readings I've deciphered and those I read on the set I'm on which I'm working. Is there a chart somewhere for this radio that I am missing?
Hey Glenn,
You're going to have to give us a better voltage chart. The XXL triode tube has pin 2 to the plate, pin 6 to the grid and pin 7 to the cathode. We will need to see the voltages for those pins. The others are filament and no connection (used for terminal connection to other circuits).
No, the 2 XXLs are not in the same type of circuit. The one at the lower part of the schematic is the oscillator and the one at the top is an RF amplifier/mixer. The plate voltage for that tube should be around 200 volts.
Best way to get voltages is to write the pin numbers of each tube on the schematic, read the voltage on each pin and record them using the name of the tube element (plate, cathode, etc.). It also helps you to number each tube on the schematic, then write the tube number near the socket. Now you won't get confused when there are multiple tubes of the same type.
Appreciate the input. Did some refinement, hopefully this is better.
Hi Glenn,
I've been looking at the fine refinement voltage chart. It appears some of the tube bias voltages are wrong. If you look at the grid of XXL tube one it connects to the bias network in the power supply. You show 47 volts and it should probably be -5. My first question is when you replaced the power supply filter cap 83, did you connect the negative lead to ground? If not then we should measure the voltage between ground and each junction of the voltage divider resistors 82, 82A and 82B. You should get 3 negative voltages.
Thanks for the reply Rod. See below.
I hope this answers your questions. I double checked the resistors along the path and confirmed they are good as well. One thing I do find puzzling is that on the XXL I have marked as 1, there is a strap from pin 6 to 7 and the 2.2M ohm resistor #7 and .01u cap #35 are both connected to pin 6 of the XXL which I do not see in the schematic.
So, I removed the "strap" and straightened it up to match the schematic and bingo, I'm up and running. Thanks for getting me focused Rob!
Excellent, hope you connected cap 35 to pin 7. Wow, we not only avoided making mistakes but found someone else's.
My final voltage readings for future readers. Line power 120v AC, using a Kaiweets HT118A digital multimeter.
Hello GRG,
Great news glad the set is working and from time to time I have seen some bad work too.
Like my Philco 51-930 that I am currently finishing up really poor soldering and some almost touching connections one was even the factory connection .
Sincerely Richard