resurrection of a dinosaur
This handsome beast was to be offered as-found but before my photo-shoot I decided took a closer look for a better description of it's condition. At first I was impressed with the high quality construction and streamlined, clean chassis detail. Featuring an exceptionally large (for it's time) electrodynamic speaker and impressive 4 tuned RF stages with push-pull 45's for output tubes.
My thoughts while disassembling this radio was that some of the designers of this and other radios late 1920's behemoths must have been former WW-I tank designers as as everything seemed to be made to withstand a bomb blast.
Next I proceeded to remove the chassis and look it over. It did not take long before I realized that someone had been here before. In spite of it's, clean unmolested appearance, one of the two component cans had been gutted leaving all the wiring dangling underneath the well shielded chassis with no diagram. So I searched for a schematic with no success. Both Riders and Official publications had one that was similar but not the same. The next two - three hours were spent drawing up a wiring diagram so I could determine what was in the large empty can. The results were two audio interstate transformers, a resistor and capacitor. I'm sure glad I did not offer this piece as is for several reasons, not the least of which....having an unsuspecting buyer getting more of a project than he bargained for and the likelihood of creating some ill will. I was now determined that this set should be heard before offing it for sale.
It was now obvious that I was going to have to do full electronic restoration if I was to bring this monster back to life.
The Next Step
Before getting too much deeper in what now to be a several day project, I needed to make sure all the special components such as the power transformer and tuning condenser were ok. Fortunately the tuning condenser was free of pot metal and the power transformer with no load checked out great on all windings. I did notice that the large umbilical cord (connecting the main chassis to the power pack) had some brittle & flaking of the rubber wiring insulation at the terminals on both ends. The cable seemed flexible otherwise and nothing was shorting or bare at the important spots so I decided to leave the cable as is and handle it with care.
The Audio Transformer Can
New audio transformers were installed inside the original can. I used the common 1:3 ratio interstage transformers that are readily available from those that cater to the likes of guys like me. The terminal strip at the opening to the chassis underside was missing, so new one had to be fabricated.
The Capacitor Can
Right next to the audio can was another can, identical in external appearance containing the filtering and by-pass capacitors. I decided to gut and replace them all. The method to remove the guts from such cans is tip #10 on my Tech Tip Page. As you can see in my photos with the top of these two cans removed, the new components only occupy a small fraction of the space the original components did.
The Smoke test
After all the above was completed plus re-stuffing of a smaller external capacitor pack and replacing two other small components I was ready for the first "play" test. The results left a lot to be desired, poor selectivity with strong stations booming in and poor control over the volume. Not too surprising as the signal and volume control design of this set was typical to others of the times. The volume control was very noisey and intermittent and cleaning it did not help. Engineers of the early days had not yet discovered AVC and none of the usual methods of volume control were very good. Most were quite simple, they just dealt with attenuating the antenna signal at the first stage. The more sophisticated control had a dual pot that increased in resistance on one section while the other section deceased. This allowed the gain of the antenna and RF stages to be controlled together. These were special parts that are often defective and nearly impossible to find or replace with something suitable of modern design. So what to do???
Make some changes in the basic circuitry! To some, this is heresy and I suppose if you were dealing with an extremely rare piece I would agree. But radios such as this are not rare and are not of high value to most collectors even if they are working. So what I do with some of these is to make a few minor modifications that I do not feel does anything except increase the value to someone that wants to use the radio for his listening pleasure. The modification I have done to this radio makes it play like a million bucks and uses all of the original circuitry. In fact, you will have to look hard with a very technical eye to even tell that it was modified. As I said, all the original parts are still in place and used (with a couple of minor exceptions). The added parts are tiny, they are hidden and they are not transistors.
A hidden AVC circuit
Adding an AVC circuit and a conventional volume control to an early radio such as this one is a great improvement. For those interested I can furnish the details and schematics to do so for a modest fee. As for this set which now works and sounds great has better sensitivity than many typical, popular modern super-hets. I offer some images of the chassis before and after modification. This modification can also be done on the Philco 90's and other radios that use that dual volume control.
How to do it
Here's a quick and simplified approach to how I place AVC in one of these early sets. First some additional components are installed in the present RF circuit stages (a small capacitor and resistor). I prefer to hide them inside the RF transformer cans as can be seen in the photo. The AVC detector circuit is all contained in the small Mallory box as can be seen in the after mod photo. For the purest who may want to put the radio back to it's all original state, these components can easily be removed and the radio put back to original. The original dual volume control must be removed and a common type be added in the audio stage as they are in a typical more modern radio.
This is now a great performing radio, tunes all am stations smoothly and clearly across the dial with great sound. The original finish is not perfect but looks very presentable. The case is sound, no moisture damage, has been kept in a clean hospitable environment. I'm offering it with the antique globe tubes as shown.
I offer schematics & AVC circuit detail material for sale > ORDER