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Philco 50-520 - Printable Version

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Philco 50-520 - Joe Rossi - 09-03-2026

After putting the Model 81 on hold, I thought I would start on the 50-520 which is a close cousin to the 81.  It is not to be.  This radio was a mess, and I am not going to try to rebuild this one from scratch.
   
   
   
   
   

This level of fix-em-up is not to my liking.  However, good has come out of it.  I paid $44 on e-Bay, and the radio had $50 worth of NOS tubes in it.  Also, the IF cans both measured per the schematic and I rescued the gold dial plate and a replacement audio output transformer. The xfrmr is not a Philco original, has the marking 5575A and the date 8-39 stamped on the metal surround.  I'm goung to open it up and replace the lead wires.  It measures the same as the Philco xfrmr.  The 500K pot and switch are good, and I'm going to drill the rivets out that hold the variable cap on the chassis.  I have a National NC-60 Special on its way to me.  In the mean time I've bought some shelving to start storing all these radios on! Icon_smile   Joe

RE: Philco 50-520 - MrFixr55 - 09-03-2026

Fire it up! If it works, then compare this one to the Canadian 81.

BTW, nice chassis holder!

RE: Philco 50-520 - RodB - 09-03-2026

Looks like the speaker took a hit, too.

RE: Philco 50-520 - Arran - 09-04-2026

A lot of sets that end up on fleabay are from estate sales, sometimes they work, others were are unfinished projects that were abandoned for one reason or another. What happened here is someone had a go at replacing the filter caps, and obviously chose to use the 450 vdc rated MIEC brand ones that many vendors seem to offer, they will work but are bulky for am already rather congested chassis. One thing these early 1950s Philcos have is that they have excellent documentation with block diagrams of each stage, as well as part placement diagrams. As long as all the critical stuff is still there you can usually make them work, the only real weak point is the mica caps in the slug tuned IF cans.
Regards
Arran

RE: Philco 50-520 - DaleHCook - 09-04-2026

Joe Rossi Wrote:  The xfrmr is not a Philco original, has the marking 5575A and the date 8-39 stamped on the metal surround.

The part number sounds vaguely familiar, but although I have a number of transformer catalogs and replacement guides, I have not been able to find it.

RE: Philco 50-520 - MrFixr55 - 09-04-2026

The Output tubes commonly used in AA5 type sets such as 50L6, 50A5, 50C5, etc. generally have a transformer primary impedance of about 2.5KOhm. Sets with 41s, 42s, 2A5, 6K6, 6F6 etc. generally have primary impedance of about 7K-10K. 6V6s generally are about 5K.

Bottom line, is that you will likely not smoke anything if the wrong transformer is installed, it will just not have the highest volume. The needed transformer for this set would be anything out of any AA5 type of set.

RE: Philco 50-520 - DaleHCook - 09-04-2026

MrFixr55 Wrote:  The needed transformer for this set would be anything out of any AA5 type of set.

Still, I would like to figure out which transformer is currently in it. It bugs me when I see a part number which seems familiar, but I can't find the manufacturer. Of course, it is possible that a previous owner replaced the original with one from a scrapped out AA5. That would certainly be true if "8-39" is a date.

On the subject of output transformer primary impedances, the stated plate impedance for a given type of tube will vary somewhat from manufacturer to manufacturer, and with various operating conditions. Plate impedance, however, is not the value which you want to use for the primary impedance of an output transformer when selecting a replacement. You want to use the load impedance shown in a receiving tube manual for the operating conditions which most closely match your set. When building my Universal Shop Speaker and Dummy Field Coil, I compiled a primary impedance table to help me to select which taps to use on the included universal output transformer, based upon tube type and operating conditions. It has primary impedance values averaged from the dozens of receiving tube manuals in my library.

RE: Philco 50-520 - Joe Rossi - 09-04-2026

Gentlemen, I too am intrigued by part numbers and I too think it looks familiar. Dale, I went through your website xfrmr catalogs to see if that one showed. For all I know it could be out of another radio and not a replacement. Joe

RE: Philco 50-520 - DaleHCook - 09-04-2026

Joe Rossi Wrote:  I went through your website xfrmr catalogs

Joe -

Those are just catalogs that I have in print. I have a lot more transformer catalogs and replacement guides in downloaded PDFs.

My go-to in looking for replacement-line parts is Sams' Radio Industry Red Book, First Edition (1948). I have it in print, but you can download a scan from World Radio History. Unfortunately it does not cover 1950 models. There was a 1950 second edition, but I have not found it online or in print. The only library holding it, as shown by Worldcat, is about 400 miles away.

RE: Philco 50-520 - Joe Rossi - 09-05-2026

Dale,  Thank you for the World Radio link, and your website.  It has been a great help over the years.   Joe

RE: Philco 50-520 - Arran - 09-05-2026

The transformer isn't a Hammond, the old ones had the name "Hammond" stamped into the top of the frame. So that would leave Merrit, Stancor, Thordarson, and Triad to look under, though there were probably more.
Regards
Arran

RE: Philco 50-520 - Joe Rossi - 09-05-2026

Odd thing, the transformer on the 81 is marked on the side metal 5070 in the same font as the transformer on the 50-520. The 81 transformer also has the Philco #32-8384 stamped on it. Joe

RE: Philco 50-520 - DaleHCook - 09-05-2026

Arran Wrote:  So that would leave Merrit, Stancor, Thordarson, and Triad to look under, though there were probably more.

Others included Freed, Jefferson, Peerless, Thurow, Utah, and UTC (TRW).

RE: Philco 50-520 - Joe Rossi - 09-05-2026

Dale, I downloaded the Sams Redbook. There section on specific radio data looks very similar to the Mallory/Yaxley layout. Joe

RE: Philco 50-520 - MrFixr55 - 09-05-2026

Sorry, Dale. I meant Loade resistance, not plate resistance. The output transformers for 43, 25L6, 35L6, 50L6, 50A5, 50B5, 50C5 all specify about the same load resistance at the usual 110V or so plate voltage, namely 2,000-2,500 Ohms. This was my rationale for stating any output transformer from an AC-DC transformerless set using a half wave non voltage doubling rectifier will work.