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Went back and checked things again, with the power switch in high these were the voltages:
80 tube 1-4 was 4.5VAC, 26 plates were 46-47 V, 71 plates were 107 V.
Put the switch in low and 80 went to 5.5 VAC, 26 plates went to 84-87 V, 71A plates jumped to 214. Brought the variac down to 100 V, switch still in low and got 4.6 VAC on the 80, 26 plates were 71-72 v, and the 71A plates dropped to 136 V. Redid the resistors and made sure they were close, changed filter cap 5, .01uF becouse I wasndt getting a voltage drop across it or at resistor point 5. Now I have 24V drop. Concerned about the plate voltage on the 71A's. being to high. Whats next
Thanks,
George
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City: Roslyn Pa
Since you have a variac put the chassis sw in hi and set the filament voltage at the 80 for 5v using the variac. This could get your voltage to fall into place or pretty close. The 26's should be 1.5vac and the 27 2.5ac. The 71A's are 5vac but they are NOT connected to the same winding as the 80 tube. As mention the 80 as 200vdc or so on it's filament and the 71A's won't work under that situation.
RCA sez max plate voltage for the 71A is 180v. If you can get the hv to 170-175v I'd call it good. That would leave the 26's at 80 some volts and that ok too.
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
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City: Irvington, NY
Also keep in mind the reference point for the measurements.
If you measure the 71A plate voltage from plate to chassis, with the chassis as ground reference, the voltage will read high. This is because the filaments of the 71A's are +40V with respect to the chassis because of the voltage drop across the bias resistor. So if you measure 220V DC from plate to chassis, the actual voltage across the 71A from plate to filament is only 180V because the filament is at +40 to create the negative bias at the grid. Subtracting, actual plate voltage is 220V - 40V = 180V.
It is also confusing because Philco listed their voltage measurements for the early sets using their set tester. This test box was used by removing a tube, plugging the tester adapter into the tube socket, and then plugging the tube back into the adapter. Because the socket had no ground pin, voltage measurements were taken from filament to plate, not to chassis. This resulted in the situation above where voltage readings differ from those taken from chassis ground.
So in other words, you need to measure the 71A plate voltage from plate to filament, NOT to chassis to get the published voltage readings. This also applies to the 26 tube readings, but difference is much lower due to the lower voltage drop (10V to 15V) across their bias resistor.
(This post was last modified: 01-07-2022, 09:36 PM by
Mondial.)
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Thanks Radioroslyn and Mondial. Measured plate voltages from the filiment and the 71's were 173V and the 26's were 73-76V, that was with the power switch in high and 4.6 VAC on the 80. Did the alignment again but still no reception. Going thru it again, had no adjustability on the neutralization.
Thanks,
George
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City: Roslyn Pa
Ok flip on it's back and find the 26 tube that is the closest to the 27 tube and the rf coils, not the one by the 71A's. Take your nice long antenna wire and clip it to pin 3 of the 26. Tune the set around and see if you can pick up a station or two. If you can leave the dial tuned to it and move the antenna wire to the next 26 tube going towards the connector. Station should get louder. When you find the one that doesn't that's the stage that need a look at and probably a coil problem. If you can't get a station a the 26 closest to the 27 look at #16 for a bad winding.
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
(This post was last modified: 01-08-2022, 05:41 PM by
Radioroslyn.)
Posts: 114
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Joined: Jul 2021
City: Pensacola
State, Province, Country: FL
Thanks alot Radioroslyn, did what you suggested and had weak signal on the RF tube next to the 27, went to the next one #2 and had nothing. I guess my coil winding skills need improvement. Rewound that coil again and saw improvement. I will rewind the next one and check again. On the path to success!
George
Posts: 114
Threads: 6
Joined: Jul 2021
City: Pensacola
State, Province, Country: FL
My thanks to all of y'all that has helped me on the project. You have taught me a lot and I appreciate the help and your patience. I know its not perfect but, wanted to see how it did back in the cabinet. Need to work on the refinishing, but that is another project. Had a short video but cant upload it.
Thanks again,
George
