[klondike98]

I combined the two 40-120C threads together as we like to keep the discussion of the same radio together. It helps with the flow of the discussion, provides additional information for the current question and makes future searches of the topic more useful to the folks that come after us. Thanks, Bob

[radiorich]

Hello David,
that is great news about the tubes source being local !
Sounds like you got good start on the radio .

Sincerely Richard

[David]

Not my radio just trying to help. David

[MrFixr55]

Hi David,

Check the cathode bias resistor, it may have changed value. That will affect grid bias, etc. Also, verify that C26 is not bad, even though you replaced it. I had a radio give very low volume and very high distortion from a leaking coupling cap years ago. This will drive grid voltage positive and cause excess plate current in the output tube. Admittedly, this would lower B voltage due to high current. Verify that your output transformer is compatible with the tube. Although drawn as a pentode, this is a beam power tube similar to 35L6 except for the base. In fact, I have a socket adaptor from 35L6 to 35A5. The transformer should have a primary impedance of 2500 Ohm.

I have never really had an issue with excess distortion running an AA5 on 120V as opposed to the 110 or 115V nominal spec for the radio.

[bluecap]

I found the problem. I had some faulty wiring on the field coil. Unfortunately, now I'm getting low voltage on the plate of the 7C6 tube. The B+ voltage appears okay (90V), but when I measure the voltage on the other side of a 220k ohm resistor connected to the 7C6 plate, I get 10V where it should be 45V (see pic). I've thoroughly checked all solder joints and components associated with the tube. Have not located the culprit.

[morzh]

Change the tube. Check the tube's bias network.
Are any other tubes experience the drop or just this?`
Is resistor 23 OK?

It is either the tube is bad, or the 220K is not 220K, or your grid bias is too large, or your cap #25 is leaking, or the wires from 220K to the tube are bad (connection). Or your socket is dirty.

[bluecap]

Thank you for your reply. I will check voltages on the other tubes, look at resistor 23 and cap 25, etc. If all else fails, I'll swap the tube.