Philips Repro Superinductance R634/15.

[pwdrive]

Excellent job Gary, do you do a full chassis strip down including valve bases etc?

Lawrence.

[Radio Fixer]

Thanks for the compliment Lawrence

No! thankfully I didn't have to do that! But the easiest way to restuff some of the caps was to take out fairly large chunks of circuitry and work on that on the bench. Many of the resistors are joined up with spirals and the like and only have short ends. Having no look a like spares I couldn't afford to damage any. Once out of the chassis I usually was able to clip on forceps as heat shunts.

Things like o/p transformer, mains switch, aerial switch and tuning mechanism all came out.

Its a really nice set. A keeper!

Gary

[pwdrive]

Thanks Gary, I have never done what would be called a full restoration yet, I mainly do what I would call a refurb ie: enough to get the receiver up to spec and useable, one day though I would like to do a "set piece" full restoration.
Somewhere on the web is a Hallicrafters SX28 where the guy had removed the lot from the chassis and did a full up restoration job, not a light undertaking for one of those receivers as they are quite complex, according to what I have read the Philips Superinductance was a very good performer for a TRF design.
It's strange now as thinks are going full circle, superhets out of the window now and direct conversion coming back in with the advance of computer DSP etc.

Lawrence.

[Yorkie]

Just re-read the Winter 2011 article Gary - a fantastic restoration covering all aspects in some depth, of what was obviously a very challenging project, with very useful hints and tips on all aspects, from re-metalising the valves to finishing the cabinet. The choice of replacement speaker fabric was very much in keeping with the set. Is the 'Mohawk' lacquer applied by aerosol can, or with a spray gun? You mention staining prior to lacquering, which must have been tricky to get the shade right. (Not a task for the feint hearted!)

Produced at an interesting time when superhet designs were struggling to gain acceptance over TRFs. (At first glance at the circuit, it could easily be mistaken for a superhet - well by me, at any rate!).

I've got a couple of low budget little TFR sets of 'minimalist' circuitry - namely, a Portadyne Pricess and a Noble, which is almost identical and use the same cabinet. Nothing like your 638A of course, but I was impressed with the performance, and lack of a reaction control, (incorporated in the volume control circuitry).

I'd agree with your view that the 638A, with its smaller cabinet, (and to my eyes, a more attractive design than the 634 'Ovaltiney'), could hardly be described as 'ungainly'.

[Radio Fixer]

Thanks for the kind remarks David. I really enjoyed doing this radio.

Yes! Mohawk, I use is rattle cans, too late now to invest in spray gun equipment although if I had done it at the start of getting into the hobby!! But I was only going to do one or two. I'm going to investigate asking a local body shop, friendly guy, for how much to spray if I do all the prep.

As to the staining I made the colour lighter than it was. The original lacquer was the thickest I have ever come across, it seemed like mm's thick so probably had aged darker. It was so dark that all the attractive marquetry couldn't be seen unless under flood lights.

No other TRF that I have ever worked on had almost constant bandwidth all the way across the wavebands and with excellent selectivity as well. That is a really impressive thing to have achieved in a domestic radio. It was Superhet performance but of course eventually production cost killed them off.

   
   

Gary

[pwdrive]

That's about as flat as you can get, I'm impressed.

Lawrence.

[Radio Fixer]

Really impressive engineering.

How's this for tracking with no adjustments made by me. Well the coils are the best and the trimmers are a mechanical work of art, being coaxial tubes over a ceramic former, so I didn't adjust any of the RF. I set the dial mechanics up to achieve a correct pointer setting at 550m. After a few iterations between this and 250m the pointer was amazingly accurate at almost any setting. It was almost spot on at 550m, dead on at 450m and 350m, half of a small division (about 1/16”) out at 250m and one small division low at 200m. On LW I only checked for R4 and the 1500m marker, or 200kHz. This peaked at 199kHz with the signal generator and frequency counter.

And that was all adjusted back in 1934!

Here's a pic of the coaxial trimmers from my 834C and one I actually took apart! the gap between the tubes would need someone like Colin to measure it! Tiny it is, mere thou. Boy! they were fantastic engineers.

   

And finally heres a couple of pics of the 634A tuning gang (on a French web site somewhere, why he took it apart I don't know but I was over the moon to get a look).

[attachment=8011]
   

Gary

[pwdrive]

Excellent stuff, the later Philips bee hive trimmers always amazed me, I think the 30's were the golden age of radio, many new materials and techniques, nice deco cabinets as well.

Lawrence.