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Philco Model 20 to restore - Printable Version

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Philco Model 20 to restore - StoneyD - 07-31-2025

Was recently gifted a Model 20 Gothic arch.  The cabinet has not had an easy life but I'm going to try and salvage it best I can.  The chassis looks to be untouched except some of the tubes have labels as to who replaced them and the date they were replaced.  Preliminary readings with DVM show the "carbon" (?) resistors have drifted high 25-50% of nominal value.  Bakelite caps show no evidence of damage don't seem to be reading open or shorted.  Tube filaments show good values, and windings reading correctly.  I have downloaded schematics, drawings, user instructions, etc. from various sources. My inclination is to replace the out-of-tolerance resistors and recap.  This is the only tube radio I own that is not working so I'd rather not purchase components in packs of 5 or 10.  Is it likely I would be able to locate a source that could supply a "kit" of the components that would be needed for this Model 20. Thanks for any help you could offer.

RE: Philco Model 20 to restore - Paul Philco322 - 07-31-2025

Try WJOE Radio I think he does assortments. Good luck. Paul

RE: Philco Model 20 to restore - GarySP - 07-31-2025

Welcome to the Phorum, StoneyD! other sources who may have kits, or can be ordered as needed are ...
https://www.justradios.com/
and
https://www.mouser.com
They may be able to help you. I strongly recommend that you replace ALL resistors and caps. There are tutorials archived here to help with rebuilding the filter cap can and bakelites. Lots of people here wanting to help you along the way! Take care, - Gary

RE: Philco Model 20 to restore - morzh - 08-01-2025

I have restored three Philco 20: one console and two cathedrals. All threads are here.
I agree with what Gary said: full recap, the can included, and carbon resistor replacement.

Also, check the wire-wound; often enough the 1400 ohm section in series with the centertap of the filaments' winding for 71A is open. As well as check it in general. This is usually not replaced even if a section is bad; the bad section is shunted with the appropriate resistor.

RE: Philco Model 20 to restore - StoneyD - 08-01-2025

Thanks for the replies. As I continue brushing off the dust in the chassis, I am finding labels attached to some of the components that I find interesting, is there an interest in preserving or those sharing labels with the group? As I go forward with questions should I continue with this same post? Also, I seem to be not having any luck when I do a forum search for the radio, I am needing information on.

RE: Philco Model 20 to restore - GarySP - 08-01-2025

Hello StoneyD. Using the search feature at the top of the page, type in Philco 20 in the Search by Keyword column. Scroll to the box labeled Search. Numerous threads came up. They may be mixed a little with other topics, but there to be found. Also, at the bottom of the Home page is a column labeled Philco Radio Library. You can find your schematic there.
Continue to post questions about the venerable 20 in this thread. Add pictures when you can. Lots of help is here to assist you along the way. Take care, - Gary

RE: Philco Model 20 to restore - MrFixr55 - 08-01-2025

Hi Stoney D,

First off, Welcome to the Philco Phorum! Please take time to read the "Phorum Rules" and "What not to Post". We are here to have fun (or "phun") and help fix (or phix) your Philco and other radios. Please feel free to navigate, explore, open doors", etc. on the Phorum website to familiarize yourself with the site. "Old Ron's Bar and Grill" is our virtual hangout where general topics such as the weather, what did you fix and "finds and losses". So belly up to the bar, get a virtual brew and shoot the breeze with the gang!

Secondly, congratulations on acquiring a Model 20. Although many were made, this was a pivotal radio for both Philco and the Industry, and a rather good performer. Although Philco was known for storage batteries and "B Battery eliminators", they got into the radio manufacturing business only in 1928 They sold about 300,000 Model 20s in total, and became the#1 radio manufacturer up to WWII, and popularized the "Cathedral" design. The radio had reasonable (about 1.5W) output, a generous sized 8" electrodynamic speaker and "Screen Grid (Tetrode) tubes in the RF and Detector stages.

Do please continue this same thread as you work toward repairing and restoring this radio. This makes it easier for both you and folks (pholks) who respond to your questions, as the history of your radio will all be in the same thread. I own one of these that I have totally recapped, another that I will eventually get to and have repaired 2 others. Several members also have much experience with these sets.

Thirdly, please post your progress and do not be afraid to ask questions; we are very happy to help!
If you look at the "Header" of this site, you will see 2 links that will be very useful. The Philco Gallery has very good photos of all Philcos from the first Philco radios to 1960. The Philco Library has links to service data (official Philco schematics) and various articles and restoration tips from several contributors, including the late Ron Ramirez who founded this site. Do post photos of your progress, questions and photos of the labels that you have questions about. (We do have a section for various labels.)

To make things easier for you, I am posting links from the Phorum that should be helpful to you:
The schematic and service data for your Model 20: https://philcoradio.com/library/download/service%20info/wiring%20diagrams/vol1/split/Part13-Philco%20Wiring%20Diagrams%20Vol.%201.pdf

You may run into several issues while restoring this radio:

Although none of the "caps" (capacitors) are electrolytic, caps can go bad in this 94 year old set and should be replaced. Hear is an an article by Mike (Morzh) on "restuffing" the Bakelite cap blocks:
https://philcoradio.com/library/index.php/shop-talk/techniques/bakelite-capacitor-rebuild-without-desoldering/ It is important to not just "bridge" over a cap, it must be disconnected from the circuit.

Although this is a TRF (Tuned Radio Frequency) set as opposed to a Superheterodyne) and much simpler, Philco sets of this vintage are notorious for the primary of the RF coils that have tube plate current passing through them to "open". Coil condition can easily be determined by ohming from the plate pin on the tube socket to the B+ at Point D on the schematic. Here is an article on rewinding Philco coils:
https://philcoradio.com/library/index.php/shop-talk/techniques/rewinding-philco-coils/

This set utilizes a "push-pull" output stage. Phase is inverted by an interstage transformer between the '27 first audio and the pair of '71 output tubes. The primary of this transformer is known to "open". Attached is an article on "bridging" transformers:
https://philcoradio.com/library/index.php/shop-talk/general/tips-on-audio-interstage-transformers/ Following the instructions for capacitive coupling of a good interstage transformer greatly improves the fidelity of the radio.

Field coils and transformers on the speaker used in the model 20 have been known to open. See the following article:
https://philcoradio.com/library/index.php/shop-talk/model-notes/the-speaker-problem-in-early-philco-cathedrals-20-21-70-90/

Ther were 2 speaker designs. The earlier one had a very stiff centering device (called a spider). The later one used a spider that looked like one of those adaptors used with 45 RPM records to adopt to the standard spindle used on record players. This speaker sounds much better than the original.

If you look at the links for these topics, you can see where I got them from.

There are several articles on repairing "cathedral" style cabinets such as the Model 20, Model 70, etc. which had similar construction.

Finally, good luck, ask any question, keep us posted and have FUN! (PHUN)

RE: Philco Model 20 to restore - StoneyD - 08-03-2025

Thanks for all the response to my post, finding some great information here.  Am posting some pix of my struggles with the damaged case and some tubes with the repair tech labels still on them, also a Dubilier label that I think came off on one of the metal can bypass condensers.  Am thinking of leaving the cabinet repairs with all the battle scars as is and am eager to get started on the chassis work needed.

RE: Philco Model 20 to restore - bridkarl - 08-05-2025

Doubt you will find a “kit” of parts. I’d just go though the schematic and order what you need.
Justradios does sell sets of resistors and caps for pre-war radios so if you think you will be doing several radios that’s an option.

By the way I asked Dave today and there apparently is no effect on his prices from tariffs right now.

RE: Philco Model 20 to restore - StoneyD - 08-05-2025

Ordered the individual components I needed so in few days I will be able to proceed with the restoration of the chassis. The case rehab is not pretty but it's the best I can do for now.

RE: Philco Model 20 to restore - bridkarl - 08-05-2025

I’m understanding the original front was trashed, but I’m still unsure about your replacement.
I think you could find a local craftsman who could make some fretwork that closer approximates the original. This isn’t totally an an aesthetic issue as I think having that thick cross will affect the acoustics.

RE: Philco Model 20 to restore - Radioroslyn - 08-05-2025

Hi and welcome,

Two quick service notes for your mdl 20. The filter caps in #26 should be replaced with mylar style cap and not electrolytics. They can't take the ripple current and will overheat causing one or more to short, not good. 

Use an ohm meter to measure the resistance from one pin on the spkr plug against the other 3 one by one. Should less than 4,000 ohms. That's the field coil's resistance (3,100)+ the output transformer (abt 500 total). It's not uncommon for the fc or 1/2 opt to be open. Doesn't hurt to know where you stand. Sometimes it's a bad connection.

RE: Philco Model 20 to restore - StoneyD - 08-06-2025

Checked the speaker assembly, field coil reads about 250 ohms. Infinite ohms on all other pins. Guessing that the primary of the output transformer is open, but will check the connections.

RE: Philco Model 20 to restore - RodB - 08-07-2025

My guess is the 250 ohms is the opt primary and the field coil, which should be 700 ohms or more, is open.

RE: Philco Model 20 to restore - morzh - 08-07-2025

Philco 20 field coil is 3.1 kOhm or so.