1930 Philco 20B Cathedrals - Printable Version

1930 Philco 20B Cathedrals - Printable Version

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RE: 1930 Philco 20B Cathedrals - PhilcoPhan1936 - 06-08-2018

(06-08-2018, 11:00 PM)Ron Ramirez Wrote: +1 what Terry said.

For what it's worth, all of the dogbone resistors in Model 20 are 1 watt. Some, such as the 500K, are overkill. Philco simply did not have anything smaller in wattage at the time.

1/2 watt resistors did not start to appear in Philco sets until 1931.

Thanks Ron.

I usually keep 1W on hand, so that's what will go in. May be overkill, but at least they'll stay cool. Icon_thumbup

RE: 1930 Philco 20B Cathedrals - PhilcoPhan1936 - 06-18-2018

I just rebuilt the big can capacitor. It went fairly smoothly for my 1st time doing one of these. Icon_thumbup

[Image: https://farm2.staticflickr.com/1829/29016848888_3579a88989_k.jpg]

The concern I have is there was a noticeable amount of tar that had leaked out onto the top of the chassis. I'm hoping it came from the cap can, and not the main transformer. Icon_eek

I was able to clean it up. Icon_biggrin

Does anyone have the ohm readings for the various windings on this transformer, so I can check if they are all good?
It's not indicated on any of the paperwork I have.
Here's the schematic for reference.

[Image: https://farm2.staticflickr.com/1765/41988515225_d517d7e442_h.jpg]

Any help or tips welcome and appreciated. Icon_thumbup

RE: 1930 Philco 20B Cathedrals - Radioroslyn - 06-19-2018

Would worry too much abt the resistances. There are a few things you can check. Smell around the bottom of the transformer under the chassis. Does it smell burnt? Remove the 80 tube and measure the ac voltage from terminals 6 and 12 and then 6 and 9. Voltages should be pretty close + or - 10v. Bad transformer will have a large difference between the ct and one end. Typically lv windings aren't an issue if the hv filters short, they take out the hv winding. With 80 tube removed plug in the set and leave in on for 10 or 15 min. Have a look at the tubes heater to be sure they are lit. Don't think the early model 20's had a dial lamp. Transformer should feel pretty close to room temperature. If it is warm, hot or smoking. That not a good sign.

RE: 1930 Philco 20B Cathedrals - PhilcoPhan1936 - 06-22-2018

Terry,

Thanks for the tip. I did as you suggested. All tube filaments light up, no excessive heat or unusual smells, so I plugged in the 80, and turned it on.
I hear a low hum, and a pop, and then next to no audio. I do hear faintly our local 50Kw talk station at 580 AM on the dial, and that's it. Icon_thumbdown

I have yet to measure voltages.
I did pull the tuning coils- IF and RF, and put new grid cap wires on them, and check the coils. They all appear to ohm out to what I believe to be appropriate resistances. Icon_thumbup

(I had the same issue of no stations before I did this, so I thought it might be one or more coils, hence my pulling them.)
All the dog bone resistors were pulled and new ones installed since they had all drifted out of spec.
My only concern is what I believe is the Output transformer or choke. (Part 21 on the schematic.)
I get uneven readings on the 2 sides. On the input side I get 1300 Ohms. On the output side, from one 71A to the other, I get 6.35K ohms. Measuring to the tap, I get 3.48K ohms on 1 side, and 2.9K ohms on the other side.
Also, my 71 tubes don't match. 1 is an ST style, the other is an older globe. Although they both check out strong on my tube tester.

I'll check voltages and report back.

RE: 1930 Philco 20B Cathedrals - PhilcoPhan1936 - 06-22-2018

OOOPS!!! Icon_redface

I pulled my Philco 20 chassis, and put them up side by side to start testing and comparing values.

I discovered a mis-wiring. I had to replace the dog bone resistors. I did it at the same time as re-stuffing the bakelite blocks.
I got the connections on a couple resistors wrong when reconnecting everything. Icon_redface

I guess I'm getting old. I really need to stop working by memory and start marking everything. Icon_crazy

She's up and running! Icon_biggrin

Now to align it. Icon_wink

RE: 1930 Philco 20B Cathedrals - Radioroslyn - 06-22-2018

>I did pull the tuning coils- IF and RF
No if or osc in this one as it's a trf.
Glad to hear you got it working!

RE: 1930 Philco 20B Cathedrals - Stall-U-Rated - 06-23-2018

Sorry to interrupt guys,
the transformer test mentioned earlier got my attention. Would this be a safe test for my 16b? No speaker and the filter cap wires have crumbled but i really want to make sure the power trans is up to snuff.. Will a removed #80 work here too?

Thanks.. Icon_smile

RE: 1930 Philco 20B Cathedrals - Radioroslyn - 06-23-2018

Should be fine to test in the same manner w/the 80 removed.

RE: 1930 Philco 20B Cathedrals - Stall-U-Rated - 06-24-2018

Thanks Radioroslyn, It worked out fine, Power transformer measured good, and ran cool. Icon_thumbup

Steve

"We now return to 20B cathedrals, already in progress".. Icon_razz

RE: 1930 Philco 20B Cathedrals - mg34.42 - 04-28-2019

so this means there will be no capacitors on terminal 5 and 6

RE: 1930 Philco 20B Cathedrals - Radioroslyn - 04-29-2019

5 appears to be unused or is a tie point. 6 has a.13 cap connected to it.