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Philco 71 Tuning Capacitor Continuity - Printable Version

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Philco 71 Tuning Capacitor Continuity - dmblackburn - 03-07-2026

I am testing continuity on the 3-gang tuning capacitor (between stator and rotor). There is no continuity between them on the 1st and 3rd section. But, I am getting continuity on the middle section. I do not see any places where the fins are rubbing in this section. Is this normal ?

RE: Philco 71 Tuning Capacitor Continuity - morzh - 03-07-2026

It always helps if you describe your cap's environment where you test.
Is it in-circuit, connected to anything or is it by itself, taken out?

This question cannot be answered without additional info.

RE: Philco 71 Tuning Capacitor Continuity - MrFixr55 - 03-07-2026

HI DM Blackburn,

If you have disconnected ALL connections from the tuning cap, there should be NO continuity between rotor and stator OR between different stators.  The rotor is in continuity with the tuning cap (capacitor) frame which is grounded to the chassis.  Review the following link to the schematic:
https://philcoradio.com/library/download/service%20info/wiring%20diagrams/vol1/split/Part44-Philco%20Wiring%20Diagrams%20Vol.%201.pdf

and the following isolated section of this diagram:
   

If you are measuring the tuning cap "in circuit", the oscillator section (green circle) would register open circuit, as the coil associated with the tuned circuit has a cap in series with it, therefore you will not see the coil resistance across the stator.  The RF Amp section (orange section) will have a high resistance as there as about 2.5 megohm between the antenna coil secondary and chassis ground (the AVC circuit).

However, the middle section, (red circle) the mixer section will have a very low resistance to ground as the secondary of the mixer transformer (the transformer between the RF amp and mixer) is directly across that section of the tuning cap.

To accurately test the cap:
It is not uncommon for the plates of a tuning cap to oxidize developing what would look like little stalagmites and stalactites on the surface of the plates.  These will touch and short the rotor to the stator section in question.  In addition, mishandling of the tuning cap will bend plates, causing them to short together.  This is the reason that you want to start the test with the cap set to the highest frequency and the plates totally unmeshed.

Also please note that you are dealing with a somewhat troublesome vintage radio.  The RF transformer and Oscillator "Tickler" coil are notorious for opening in these radios, requiring you to rewind the offending coil.  

Hope this helps.

RE: Philco 71 Tuning Capacitor Continuity - dmblackburn - 03-08-2026

Thank you all for your very thorough comments and the time you took to assess my situation. Yes, the capacitor is still connected in circuit. I will plan to take it out of circuit and do some thorough cleaning. I will most likely need to restring the dial and add a new spring as the knob does not always turn the capacitor in all places.
One question regarding one of your points: Grid leads can remain soldered to the cap but removed from the tubes.) Are you referring to the wires that connect to the dial light or something else ? Thanks again.

RE: Philco 71 Tuning Capacitor Continuity - dmblackburn - 03-10-2026

I removed the tuning capacitor from the chassis and performed the continuity testing and resulted in infinite readings on all three sections. To mitigate the difficulty in turning (slippage), I applied some rosin to the dial string as much as possible and applied some Deoxit D5 to the areas where the spring clamps were rubbing on the shaft. Worked the knob back and forth several times and for now not getting any slippage at all.
I also have a better understanding of the capacitance changes that occur when rotating the shaft (changing stations). I took pF readings with a L/C meter and could see the changes in capacitance when turning the tuning capacitor. 14.7 to 348.7 pF on the RF section, 18.49-348.1 pF mid-section, 20.5-346.4 pF on the oscillator section. I turned the compensating condensers also and saw the changes in capacitance. 
Question: Should the pF ranges be consistent among the three sections ? Or maybe, this is what happens when the set is properly aligned

RE: Philco 71 Tuning Capacitor Continuity - dmblackburn - 03-10-2026

I did an alignment after getting the tuning capacitor back into the chassis. I used an EICO 324 signal generator and put a Simpson 260 across the speaker wires (AC voltage). Was getting a fair amount of volume on the lower end alignment but reduced volume on the high alignment.
I have replaced all capacitors in the Bakelites and replaced the capacitors in the tone control. Any resistors that were out of tolerance were replaced. This Code 121 only receives 1 station at 620. Nothing received on the high end around 1410 (a very strong local station). I estimate I'm getting about 10-15% volume on the one station that I can receive.
I have performed ohm readings on the coils and they are within specifications. Tubes are good to very good (EICO 666)
I am still using the dim-bulb setup for fear of doing any damage to the set (using about 90 volts).
Voltage readings on the tubes are close to spec relative (realizing I'm not using wall voltage). The CG-K readings are concerning:
44 RF 0.15 (Measured) 4 (Spec)
36 Detector Oscillator 8.5 2.3
44 IF 3.9 0.2
37 Detector Rectifier __
44 Audio 2.2 0.3
42 Output 16 0.2

RE: Philco 71 Tuning Capacitor Continuity - dmblackburn - 03-10-2026

The format did not use my spaces between the measured voltage and spec voltage. There is a space between the measured and spec voltage

RE: Philco 71 Tuning Capacitor Continuity - morzh - 03-10-2026

Ditch the dimbulb.
I cannot stress that enough - this is a crude "exsessive current draw" tester, it is not good for anything else.
And whatever alignment you performed with that dimwit concoction, guess what - it is not fully valid. The alignment needs to be performed with the nominal power voltage.

About the tuning cap's sections: itis different for different caps.
Some actually intentionally use different size and value sections.
Some use the same.
The manufacturing tolerances 9this is not exactly a high-precision part) of each section will vary as much as any signle-section cap would. Yours is not bad.

And the differences - this is what the compensators are for. They compensate.

RE: Philco 71 Tuning Capacitor Continuity - dmblackburn - 03-11-2026

Thank you for your response. Makes total sense.
I performed new voltage readings after doing an alignment with the radio plugged into the wall. The wall voltage measured 122.9 VAC  when I did the readings. Incidentally, I can only get that one station at 620 with a little bit more volume. Nothing received on the top end of the dial.
I have attached my voltage readings. Not really understanding the CG-K readings. They are way off unless I'm not using the correct technique. I'm measuring from the CG cap connected to the tube on the capped tubes.

RE: Philco 71 Tuning Capacitor Continuity - dmblackburn - 03-11-2026

Some additional information that may be useful.
The voltages across the 13,000 ohm resistor (P/N 59) 266 VDC to 123 VDC
I substituted a 10K resistor for the 15K resistor (P/N 18)
All of the 36 tubes I have in stock measured good off the scale on my EICO 666. I am using the updated tube chart from BAMA.

RE: Philco 71 Tuning Capacitor Continuity - morzh - 03-11-2026

The 59 will be hot, but I guess this is as intended: the screen grid voltage of the 36 or 44 tubes are much lower than the 42 one.