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Philco Model 20 Lowboy - Printable Version

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RE: Philco Model 20 Lowboy - WallaceRoger - 07-01-2017

This new mail carrier is driving me to drink. I finally picked up the new transformer waiting for me at the post office.

I was hoping there would be some sort of diagram with it explaining which wire is which, but no dice. The new part has five wires like the old one... two are green, a black, a red, and a blue. From looking at the schematic, it looks like the two greens are for the 71A tubes, the black goes to point #1 on the filter condenser block, then red and blue are for the 27 tube and the bakelite block. I don't want to hook this up wrong and kill myself or fry my radio! Which color wires match up to which of the old interstage transformer wires? My knowledge isn't currently enough for me to figure it confidently.

Photos of old and new are below.

   

   

RE: Philco Model 20 Lowboy - KCMike - 07-01-2017

https://www.tubesandmore.com/sites/default/files/associated_files/p-t124b.pdf
This might help you.

RE: Philco Model 20 Lowboy - Radioroslyn - 07-01-2017

The wire are a standard color code. red B+, blue plate of the 27, Black grid bias, and green grid of the 71a's. Polarity doesn't matter on the green wires (doesn't matter which of the 71a's they go to).

GL

RE: Philco Model 20 Lowboy - WallaceRoger - 07-01-2017

I studied the schematic... figured it out. All wired up and it does make a difference. The volume knob now actually seems to have an affect on the volume. When I tune it all I get are various levels of hum/buzz. I'm not getting any stations. For an antenna I just used a 15 ft piece of wire. Didn't try grounding it.

I'll go through and test everything again.

RE: Philco Model 20 Lowboy - Radioroslyn - 07-02-2017

Simple test. Put knob on the tuning shaft. With the set on tune it w/one hand and place a finger from the other hand onto the grid cap of one of the 24A tube and hear if you can get any stations. If not do it again w/the finger of the other 24A cap and hear if you can get any stations. Really we're just testing your magnetic personality. You should be able to pull in the BIG 8 from where you are.

RE: Philco Model 20 Lowboy - morzh - 07-02-2017

The key point: do put the knob on the shaft. It's a safety measure.

RE: Philco Model 20 Lowboy - WallaceRoger - 07-02-2017

I powered up this morning to try this test and immediately picked up WLS! Some noise, but it was coming in. Lots of noise beyond that on the dial. Lower on the dial, I barely grab another station, but it's very faint. I should add that this was happening WITHOUT me touching the 27 tubes at all, the station just came in right away.

I listened to WLS for a few minutes, tried tuning and it all faded to static. Tried tuning back and forth, just static, not even WLS anymore. I didn't see any smoke or smell anything cooking.

I noticed that the volume knob doesn't turn as freely as it seems like it ought to. It's somewhat difficult to turn in one direction and makes small sounds occasionally like a spring popping. Maybe this is an issue?

It's weird that I was getting a station and then it just went away as the set ran.

EDIT: I shut it off, waited a few minutes, powered back on and listening to WLS again... then 5 minutes in, the station drops out and just getting the radio hum. seems really odd.

RE: Philco Model 20 Lowboy - morzh - 07-02-2017

Have you a) tested all tubes, b) checked all RF coils continuity?

RE: Philco Model 20 Lowboy - WallaceRoger - 07-02-2017

All tubes were tested for filament continuity with a multimeter as well as normal tube tests on my Conar. I came up with a bad 24, so the one in there now is a replacement (I tested that too when it arrived, tested good). The tubes I have are 24 rather than the later 24A, but I don't think that would matter as long as they all test ok.

The 27 that came with this radio gave me a "?". I bought a replacement from the same guy as the 24 "just because". It was listed as being 90% and tested on a Hickok, my Conar gave me another "?" on it. I tried swapping the replacement 27 tube in now and volume overall is much quieter, the original one seems better. Maybe they're both no good.

The RF can next to the 27 tube gives me 25 ohms or 4kohms, depending on where I place the leads. The other two cans seem to give me about 6-7kohms no matter where I place the leads.

RE: Philco Model 20 Lowboy - Ron Ramirez - 07-02-2017

...too bad you can't tune in WLS Musicradio from the 1970s...

RE: Philco Model 20 Lowboy - WallaceRoger - 07-02-2017

Ron, that would be great. Here in Chicago, there's not a great deal on AM anymore except sports and talk radio.

Terry, thanks much for the phone call. I put the chassis back in the cabinet and ran a ground lead to the center screw of the outlet. That seems to have helped me pull in more stations. I'm listening to (background noisy) WBBM, will see how long it holds out for. I'll give your screen cap finger test a try if it ends up cutting out.

RE: Philco Model 20 Lowboy - morzh - 07-02-2017

Greg,

All the RF cans are xfmrs and have primary and secondary, they are at the sch on the left of all tbree 24 tuves. Both prim and sec should give you low ohm readings, certainly not​in kOhms. Make sure they do.

RE: Philco Model 20 Lowboy - WallaceRoger - 07-03-2017

Hi Mike,

Terry and I worked through this on the phone yesterday (that man has the patience of a saint). Now I'm at work and can't recall exactly what we did, but he was telling me the RF cans were ok after he walked me through which points to use for the resistance check. What we settled on as a possibility is that one of my tubes has a fault in it that doesn't materialize until after it gets hot. I need to clean all my pins and contacts (and the volume pot) with contact cleaner, too.

I could re-test the RF cans again though, wouldn't hurt. Which pins/locations do I use to test the resistance of each can?

EDIT: Actually, maybe it would be a good idea to test when cold, then turn on and test again after the signal drops?

RE: Philco Model 20 Lowboy - morzh - 07-03-2017

(07-03-2017, 10:40 AM)WallaceRoger Wrote:  Terry and I worked through this on the phone yesterday (that man has the patience of a saint).

That he does Icon_smile

I think he is right, if you went through it; it could very well be what he thinks it is, which is a hot tube defect.

I wonder if this can be tried (only in case you have no spare 24): 20 is a TRF and even without the first tube if the antenna or the finger are connected to the second tube the same station (strong local) could be received. Or so I think. If this is the case, you could substitute the 24 tubes in the same socket (say, the second RF tube) until the defect shows up/disappears, and figure out which tube causes that.

RE: Philco Model 20 Lowboy - WallaceRoger - 07-03-2017

I think I might buy a spare 24 tube. I can always resell it if that winds up not being the issue. I'll either do that or give the "missing tube" test a try and report back.