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Reese,
I can't thank you enough for effort your putting forth here.
I'll try to be as concise as I can. I won't do any changes until I hear back from you on my findings and the changes that need to be made.
I'll add a side note or two if it seems to pertain.
1. The tech who wired this for 120VAC made it into a hot chassis set. Notice that one side of the line goes to the power switch and the other side of the switch is grounded to chassis. It is dangerous like this in that if the hot side of the line goes to the switch, the chassis with the switch on will be a shock hazard with respect to ground. Even with the switch off it will be a shock hazard if the hot side of the line goes to the rectifier as the chassis would be hot back through the heater string. You can find the other errors and get the radio to work this way, but you should use an isolation transformer between the set and line. Also you should be insulated from a concrete floor and be careful and don't rest your arm or other hand on the chassis when taking readings. The live chassis can be made safer with a floating B- bus but I'd say get the set working first and tackle that as a later project.
2. 25Z6: pins 3 and 5 are tied together and one side of the line cord goes to them.
The neutral side (I traced this side back to the plug and marked it to ensure it is always plugged in as neutral) of the line cord is attached to pin2, jumped to pin3 and jumped again to pin5 of 25Z6.
3. 25Z6: pins 4 and 8 are tied together and go to the + side of the first electrolytic cap. The - side of this cap goes to chassis ground. Be sure you have + and - correct on all electrolytics. It looks like you have two electrolytics with their + sides tied together. Why is that, and where are they in the circuit? There's another underneath them. What are the mfd values and voltage of each?
Yes…pin 4&8 are tied together and go to the (+) of the first electrolytic. I assume your referring to the 2 brown electrolytics, 39uf/400V each. They replace a 40mdf/40mdf/150V cardboard can cap that had two (+) leads and a single (-) lead. The 2 (-) leads (striped side of labels) of the new lytics were tied together to mimic what was removed. There isn’t another lytic below them, unless you mean the blue one, 15uf/400V out to the side…semantics?
Note: The 130.5V tap from the lower transformer is also attached to pin 8 of 25Z6
4. 25Z6: cannot see but there should be an approximately 1000 ohm 1 watt resistor also connected to the + side of the first electrolytic cap and the other end of the resistor should go to the + side of the second electrolytic cap. The - side of this second cap goes to chassis ground. Where does the + side of this second cap go?
I do not have 1000 ohm 1 watt resistor spanning to two (+) leads of the elecrtolytics.
The 2 (-) neg leads of the elecrtolytics (which are tied together) go to pin 8 of the 6Q7 tube. Then pin 8 is jumped to pin1 which is soldered to the chassis ground tab.
The (+) lead of the second electrolytic goes to pin 6 of 6Q7.
5. 25L6's: tube at front of chassis near speaker plug let's call tube A, other one tube B. Tube A has a wire from nearby input transformer going to pin 5 (grid 1.) Should be another transformer wire to pin 5 on tube B? What is resistance between the two pin 5's? Is there a third wire from the transformer on the same side as the other two and if so, where does it go? What is resistance between this wire and each of the two other ones going to the two pin 5's? Transformer can't be open or shorted or there'll be no audio.
The resistance between pin 5 on the two 25L6’s is 276.1 ohms
The third wire goes to pin 1 on 25L6 tube (A)
The resistance on the third wire, pin1 to pin 5 on 25L6 (A) is 141.7 ohms.
The resistance on the third wire, pin1 to pin 5 on 25L6 (B) is 134.3 ohms.
Note: Pin 1 on tube A is also attached to the chassis ground tab.
6. 25L6's: each tube should have separate wire from pin 3 (plate) to speaker plug. Another single wire from speaker plug to both pins 4 (screen) jumped together. Pin 4 on tube B appears to have another wire which should be going to B+ (the + side of the second electrolytic.) Does it?
Yes…pin 4 on 25L6 B has a wire that attaches to the (+) lead of the second at the pin 6 of 6Q7.
Pin 4 of 25L6 B has an additional wire that goes to the opposite side of the afore mentioned (upper) “3 wire input xfmr”.
7. Unplug the speaker. Determine which wire going to the output transformer on the speaker is the one that goes to pin 4 on tubes A and B. Connect one lead of your ohmmeter to this wire at the plug. Check the ohms between this wire and each of the other two wires going to the transformer in turn. They should be about the same.
133.7 ohm & 153.7 ohm
8. 25L6's: there is a resistor (what ohms?) from pin 8 (cathode) to ground on tube A, and an electrolytic cap (what mfd. and volts?) from same pin 8 to ground. Is there a similar arrangement on pin 8 of tube B?
Resistor from pin 8 to grnd…620 ohms
Electrolytic (blue) 15mfd/400V.
Pin 8 on 25L6 B is jumped to pin 8 on 25L6 A
Whew!
Hope this answers your questions and gets us closer.
Thanks again.
Martin
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