[RGallahue]

Have been working on a Model 65.  Have lurked out here on the site for some time, and you folks have been helpful in the past, so here goes:

I have rebuilt a number of Philcos in my time but this is my first TRF unit.  Doing all the usual repairs, caps, (yes, including the power supply) and all out of spec resistors.  Making progress but have run into a couple of issues.

First, the Philco 3518 choke is a shielded 150H, 10ma unit with a DC ohms measurement of 4,000 ohms.  Mine reads a shade under 83 ohms, so I would suspect it has a short.  My question is regarding a replacement as chokes with a 150H rating are apparently rare birds.  Checked Hammond, etc, but have not been successful.   Any ideas or does anyone have a 3518 they might part with?

Secondly, although I have yet to fire this old beauty up, I did check continuity across the speaker connector and got continuity but some rather large resistance measurements; on the small pins a rather unstable 40K ohms and the large pins read a steady 240K ohms which seems somewhat high to me.

Of course the schematic is unhelpful, so not sure what to expect, but I do suspect the coil and what I presume to be the output transformer which sets atop this glorious piece of cast iron. Anyone out there with Model G that might check theirs?

I do appreciate it...

[Radioroslyn]

If you can't find a suitable choke replacing it w/a 4K resistor and adjusting the value of 20 to eliminate hum. As for the speaker sounds like the field coil and output transformer are open. Both are rewindable a member did one a few months ago. If you have a lot of time and patience the opt is doable but is a job.

[Phlogiston]

In addition, this early set is prone to bad/intermittent crimp connections. So check connections before parts replacement. The oddly colored dog-bone resistors are usually way off. Get the Philco color chart because the colors are not industry standard (if there was one, at the time).

[RGallahue]

Radiorosyln: Well, I was certainly not the first one in this chassis. I had noticed that the choke was not original and apparently the last repairer had noted the choke had failed, but left it in circuit and compensated by putting a huge 16MFD electrolytic in parallel with the power supply capacitor block on the other side of the chassis at the speaker connector. That is much like you have suggested with the resistor replacement ( I am thinking a 5 watter or so), and I may need to go back to that sort of a brute force arrangement.

Phlogiston: One dog bone in the bunch at the power supply capacitor block, but it was in spec. The strangest thing to me was the combo resistor/capacitor units. Never had run across those before...

Hammond does make an open framed choke (156C) which is 150H, 8ma and 3700 ohms that might work in this application, but as the unit that is on there is fully shielded and enclosed, I think that I would be expecting some issues using this as a replacement? Everything topside on the chassis is pretty well shielded in any case. Thoughts?

The speaker is another story, and while I have not gotten there yet, if whoever it was that did some rewinding of a Model G speaker would come forward, I would certainly appreciate your info as I may have some questions a bit further down the road. I did do a search and could not find the associated posts. Otherwise, if someone has a speaker (working!) that they might part with....

Both of you, appreciate the assistance. Anyone else with any thoughts is welcome to chime in. Again, my first TRF radio, so I am wandering around in terra incognita (a.k.a. lost in the woods).

[Radioroslyn]

https://philcoradio.com/phorum/showthread.php?tid=21906
https://philcoradio.com/phorum/showthrea...#pid173866

[RGallahue]

Well, I am back.  After replacing the speaker in its entirety, all power and bypass caps, all out of tolerance resistors, one filter choke and an interstage transformer, got it running pretty well and them ran into a problem with the one filter choke that had checked out good initially.  The choke in question (#21) is a Philco part number 3422,  6.5H rated at 150ma and 200DC ohms.  I see replacements which are close as both Triad and Hammond make a 6H choke rated at 200 ma and 150 DC ohms. 

If I substitute with either of these chokes, I am just a bit short in the Henrys department as well as resistance.  Would this be close enough without additional modifications?  Do I need to add the 50 Ohms in series or will the replacement choke be a sufficient substitute?

There is a 7H choke from Hammond that is rated at 150ma like the Philco, but its DC resistance is 100 ohms.  Would this be a better bet with a 100 ohm power resistor in series?

Any assistance is greatly appreciated.  This Model 65 is my first TRF radio, and it has been quite a chore...

[Phlogiston]

I think that the 6H chokes will be fine. The DC resistance doesn't actually = the impedance, but close is good. When your done just check the LOADED B+ to make sure it isn't too far off (before thinking of adding resistance).

Russ

[RGallahue]

Well, the 6 Henry choke took up a bit of real estate, and between that and the open interstage transformer, the radio did lose some of its original appearance, but up and operating rather well. B+ was good, no need to add resistance. Been quite a trip working on this one, and I thank both of you, Radioroslyn and Phlogiston, for your assistance.

Now to get the scalloped grill cut, stained and replaced. That may be the hardest part of this yet.

[Ron Ramirez]

RGallahue, let me ask you a question. Does your model 65 break into oscillation if the volume control is turned too high? I just completed mine, and it does. I am just curious. Thanks.

https://ronsradios.com/2021/08/02/philco...rs-part-1/

[RGallahue]

Sorry, Ron.  Have been offline while I was awaiting the grille to come back and fixing up a Crosley D-25 for sale on Ebay to make back some of my investment in this Model 65.

Tried out a number of scenarios, and could not drive the tubes into oscillation regardless of the volume setting.  I will tell you that one of the 24 tubes was bad, so I replaced with a set of 24a's.  Not sure what you are running, but perhaps the 24a tubes are not as susceptible to oscillation when driven hard.

Outside of that, if there is anything you would like me to test, let me know.  Turned on my email notifications.

Also saw that you rebuilt the transformer. That was the only item I did not have to touch on mine, but also did not have to work on a mouse house either.

[Ron Ramirez]

Interesting. I was using Arcturus Blue 124s in my 65.

(It came with a full set of globe Cuningham tubes. Oddly enough, when I tested the tubes, the two 324s and the C-327 were all weak/bad. The globe CX-345s and CX-380 were all good!)

Anyway, I tried two 24A tubes and it still broke into oscillation if the volume control was turned up too high, so I reinstalled the Arcturus Blue 124s. An RCA UY-227 replaced the Cunningham C-327, so my 65 still has all globe tubes.

I'll have to look in my tube stash and see if I have any Cunningham 24s or a 27, so that it has a matched set again.

But all of that does not answer the oscillation issue. ???

[Phlogiston]

Make SURE that your tube tester is putting out at least 2.5V when testing these tubes (especially the 245) most testers are calibrated around 6.3 or higher settings and sag at 2.5V. The old story that the manufacture and/or  expected results (Mhos) are designed to make up for that is B.S. - sorry.

I will often insert my VOM probes into another sockets (big pins) while doing these tests to actively monitor voltage. A lot of good tubes have been thrown away - - 

Russ

P.S. TIP - I set my 533 on 3V for these tubes and I get about 2.5 on the filaments - Saves me time, might work for you, just need to check.

[Phlogiston]

There are slight differences between the 24 and 24A (fast  warm up). As I recall, there is at least one radio (a Crosley I think) that will not work properly when its 24 is replaced by a 24A.

Russ

[RGallahue]

Ron,

Not an answer yet on the oscillation matter, but I do have a question about the filter can, terminal #1.  When I got into the radio, I found that at some time in the past the wire had been removed as I presume that section of the filter can had failed.  I can tell you that the chassis was rather hacked, looks like yours fared better even with the mice.  When I rebuilt the can (I was not lucky enough to have an already empty can around ) I routed a wire under the wiring harness back to the filter choke (Part #21) as per the schematic, no issue, but I do not believe that was where that was originally attached. I saw the photos but cannot make out the connections exactly...

Just curious.  If you have a chance let me know. 

As to oscillations, in looking at the schematic, I would think the bypass caps would take care of that. That is a puzzle. Maybe some else has the answer, but if I come up with a possibility I will let you know.

[Ron Ramirez]

I've put my 65 away and am busy helping wife get ready for a yard sale so there is no chance of my being able to open it up again anytime soon.

However...

Looking at the schematic, terminal 1 of the filter condenser block connects to one of the filament pins of the 280 tube (which also connects to terminal 1 of the power transformer); to one side of filter choke (21), and also to terminal 2 of the filter condenser block.

Parts 2 and 3 of my model 65 rebuild are on my blog; I'll be posting part 4 tomorrow; part 5 Friday; and parts 6 and 7 next week. I don't know if any of those photos will help, but feel free to look at them. A tip: Depending on which browser you use, you can right-click any photo on my blog and select "Open image in new tab" or "View original image" and you will then see a larger image.

Regarding the oscillation in my set, I've replaced all of the bypass caps. The only capacitor I did not replace is one mica capacitor in the detector circuit, part (15).