[TNTrawlerman]

Hello All,  I am a newby  here, and looking for help on a Philco Model 65 that I am working on.  I have found the wonderful restoration project that has already been posted, and have read it from end to end, and gotten a lot of help as a result.  On the chassis that I am working on. the power supply choke #21 is burnt out, and despite noble efforts, is beyond repair.  I have found the reason that this happened, and rectified that, but I have two questions that I would like direction on, those being (a) what would the likely inductance value of the choke be, and (b) what is the purpose of the capacitor in parallel with the choke?  I understand the filter effect of the ones that go to ground before and after the choke coil (Pi type filter) but not sure of the purpose/theory of the one across the coil. Is it intended to form some sort of resonant circuit?
Thanks in advance to anyone who can give me a steer on this.
Ken

[morzh]

The cap in parallel could be left out.

The theory goes that since the cap has voltage lagging current and the choke is ortherwise, a cap could be chosen such that the ripple voltages will cancel each other out.
It has little or no effect and today most of us drop the cap.

The choke value usually is in units to tens of H.
AI gave 4-6H and 230 Ohm.

https://www.mouser.com/ProductDetail/Ham...61EBX0Y%3D
I think this one is 108 Ohm (found my own post earlier)
https://philcoradio.com/phorum/showthread.php?tid=7386

You could pad the resistance by using an extra resistor.

[RodB]

Welcome to the Phorum, Ken. The Phorum library has a chart of chokes (say that fast) but it's not all inclusive and I did not find yours in the list. Judging from the coil resistance of 3200 ohms, I would say it's in the range of 50-70 Henrys. If you want to get the power supply to supply power while waiting for a replacement choke you can substitute it with a 2.2K resistor 8 watts or more. In addition, you can double the capacitance of the filter capacitors. When you are ready to replace the choke, you can remove the supplement caps.

That parallel bypass capacitor across the choke was put there to decrease the possibility of voltage spikes or oscillation. Maybe rf interference too. Could be some dozen other excuses for it. You can leave it out or replace it.

[RodB]

Oh Mike, my speaker chart from the library shows the Philco 65 choke at 3200 ohms. Maybe it's a misprint. It would seem yours is more acceptable.

[morzh]

Rod

I am not sure. There are two chokes. One is the field coil; that one is sure 3200 Ohms. But he asked about the #21, the filter choke.
The choke itself ... I asked the AI. The answer seems plausible.
The P/N is 3422-D.

AI answer:

The filter choke in a 1929 Philco Model 65 (part number 3422-D) typically has a resistance of approximately
200 to 230 Ohms.

I only found Parts list for 96 on Nostalgia, it is 3422 indeed. They are supposedly the same across this series of early 1929-1930 TRF consoles plus 111-112.



Also I found this on eBay:

Philco Filter Choke 3422-D (230 Ohms) Clean! (1929) fits many model Radio or Amp

Offered is the Philco Filter Choke type 3422-D. The choke is clean and in good condition with only a few blemishes here and there. It measures 227 ohms on the DMM. Used in Philco models 15, 40, 65, 76, 77, 87, 95, 96, 111, 112 and possibly others.



----------------



And no, it is not a misprint. Like I said, there are two chokes; yours shows the Field coil at 3200 Ohms which is correct, but we are looking for the filter choke.

[morzh]

For instance, the Philco 70 choke 4819 is this

7.5H 285 Ohm, which is similar.

[morzh]

Right now on eBay:

https://www.ebay.com/itm/285419459794
4819 (for Philco 70) It is a 130mA chole so will do just fine provided the size fits.


This is supposedly the exact part. But I'd be a bit cautios as this is from such a radio and how much life it still got it in, is anybody's guess.

https://www.ebay.com/itm/277290444534?_s...R865ya2RZg



So are

https://www.ebay.com/itm/266210687401?_s...R86S7Pb6Zg


and


https://www.ebay.com/itm/267221194007?_s...R86S7Pb6Zg

[RodB]

That's the whole thing in a nutshell. Looking good, Mike.

[TNTrawlerman]

Many thanks to all who responded, all very valuable info. At 81 years old, I have been off the bench for a LOT of years, but now back into it as a hobby to replace having sold my boat to eat up time. I am going to give a power supply transformer that I mistakenly bought a bunch of, and give that I a try as a choke, and use larger capacitors on the downstream side. This primary measures 7.4 H and 338 ohms. I am always leery of some of the old units for sale wherever, as they may be as close to biting the dust as the one in the set. I did an autopsy on the defunct one, and found that corrosion was endemic inside it, with lots of copper going green, especially the wires that joint the terminals to the windings. Also, the winding potting material so hard that virtually impossible to dig into successfully to find and reattach wires to the thin copper windings. I will let you know how that works out. Still a lot to do before I give it the initial "smoke test".

[morzh]

I am not a big fan of using power transformers as chokes, but might work fine. The power transformer works with AC (ecpecially those centertapped) and the choke works with DC bias.
Make sure the primary is supposed to withstand 100-120mA (it likely is, as this would make it 12-14W and the xfmrs are larger).
Either clip or reliably wrap in insulation the secondaries. Those could have large voltages across them.

Again, the 1st capacitor after the rectifier should not be increased. After the choke it can.

[TNTrawlerman]

Will do.  I have insulated the secondaries with plastic.  I realize that the the 1st capacitor should be the same as the original design to not overload the rectifier tube, and as such have used the same value.  I have increased the value of the capacitor after the choke to 10 uF in the hopes of compensating for any lack of filtering effect from the choke.  I will let you know what the outcome is when I get to the power-up stage.  Still a LOT of work to do.  I will bring the power up with my homemade digital watt-meter that gets its power from a variac, and I bring it up slowly with an eyeball for excess current and/or other nasties happening.
Many thanks for your expertise.
Ken

[TNTrawlerman]

Just a quick reply that the old transformer worked like a charm. The radio works like a charm now on the remaining two AM stations that are near enough to Maryville TN to receive with any decent volume. Thanks to all for the advice and help.