The PHILCO Phorum

I've had this 38-690 sitting around here, literally, for years. I had done nothing with it at all during that time.







So, back in February, I decided that I should check it out and make sure it was ship-shape and good to go.

To be brief...it wasn't.

Oh, I could plug it in, turn it on and (barely) hear my home AM transmitter...but that was it.



Notice the BNC jack in the back of the chassis, to the left of the antenna terminal board. Notice also that one of the screw terminals on the antenna terminal board is missing, and that two wires are connected to the other two screws. Keep this in mind as this thread progresses.



Close inspection revealed the speaker cables were dried out and in poor shape. I also discovered that the same was true for the tuner-to-amp interconnect cables.

So here we go with a...ummm...an adventure.

I started the process by putting the amp chassis on the bench.



Let's look underneath.



A hack job. Very poorly done. And what was dangling at the top of the chassis?





What an incredibly sloppy way to attach a fuse to this receiver.

And look at the woofer plug:



Much of the Bakelite plug has been broken away.

Yup, my work's cut out for me this time...

I began by making new speaker cables. Here's one of the new tweeter cables, next to one of the old ones for comparison.



I also made a new woofer cable, using a 1939-40 or so Philco speaker connector to which I added a fifth terminal (it only had four while the 38-690 has five terminals; the plug is made in such a way that a fifth terminal may be easily added, however).

Then, I turned my attention to one of the power transformers. If you noticed in a couple of the images above, the retainer ring had come off and the socket was basically just dangling in air.



Those old rectifier wires were badly dried out from age and heat...as I knew they would be.



So...I proceeded to shrink wrap the four wires, running double thicknesses of tubing up inside the paper wrapping as far as I could.





Since I had the upper bell off anyway in order to work on the wires, I sanded down and repainted the bell, and the tube socket retaining ring, with Rustoleum Flat Black paint.

Next, the bell was reattached to the transformer (once the paint dried, of course).





Unfortunately, something was wrong with the socket itself.



As you can see above, it was broken! This was just a carbon track waiting to happen (definitely not a good thing). Fortunately, a trip to the junk pile yielded another, good socket from a 1937 Philco power transformer.

It was difficult to get the "ears" bent just enough to hold the socket and retaining ring in place, as some of the metal used to form the "ears" was gone. But I persevered...and finally succeeded.

Next came electrolytic capacitors.

This chassis was missing some of its original electrolytic cans. For those that remained, I cut them open and restiffed as many as I could with film caps. Unfortunately, there was one on the amp chassis (and, later, one on the tuner chassis) in which I had to use electrolytics as the film caps I had bought would not fit!

Here's one in which the film caps did fit:







The cans which were missing on the amp chassis were mainly single 8 uF caps. These were replaced with the motor caps Bob Andersen had recommended in another thread.

As for the 18 uF cap, this was restuffed with two Solen Fast 8 uF caps connected in parallel to equal 16 uF - close enough.

The finished amp chassis:





No, I didn't restuff any paper caps. Pardon me. There were no paper caps under the chassis to restuff - the hacker, er, "repairman" had removed them all.

Now, I needed a fused AC plug that looked like the original plug. This too was missing in this radio.

Fortunately, a farm and home store which also sells electric fencing had just the plug I needed.



This new plug is nearly identical to an original Elmenco fused plug:



Of course, the new one is made in China. Isn't everything these days?

Next up: the tuner chassis.



Yes, the dial scale is cracked.



Take a good look at the top view of the chassis. Somwehere along the line, someone had removed several of the tube shield bases so that metal and/or GT tubes could be used. This would present a bit of a challenge - especially for one tube socket which required a wire to run through the rivet which helped to hold the socket and shield base in place.

But first...I will tackle other issues on (and in) this tuner chassis.

Stay tuned...

Excellent thread, Ron. Really enjoyed following your progress on the amp chassis. Learned a few things too, which is always a good thing.   Looking forward to your work on the main chassis.

Ron;
  I will have to keep my eyes open for those newer fused plugs, they used to sell aftermarket ones like that for use on TV sets. Though I personally don't think it's necessary in most instances, they are a much more elegant alternative to the hacked in fuse holders I see some people adding to vintage sets, especially the 12 volt plastic automotive ones that are not even rated for 120 volt use. As for the tube shield bases someone could make a cottage industry of making reproductions of the 1937 style ones, given how many of the 1938 and later ones seem to get hacked. Those later ones are a stupid, and might I say, vindictive design, they rub me the wrong way much as the silly security screws that seem to infest modern appliances, if I own it it's none of their business to keep me from opening it up, just as it was none of Philco's business whether someone wanted to use metal tubes in one of their sets.
Regards
Arran

By now it's mid-March.

The amp chassis was fairly easy and painless to rebuild, even considering the new woofer and tweeter cables which had to be made and the repair work to one of the power transformer sockets. It has a new power cord with the proper fused plug as well, with 2 amp fuses in place as per original.

Now comes the fun part - the tuner chassis.

Remember those two wires connected to the remaining two screws on the antenna terminal board? Remember how I said the radio was just barely picking up my home AM transmitter (and nothing else) before I started working on this set?

There was a good reason for that.





(These photos were taken after removal of the tuner chassis' RF unit.)

The hacker - er, repairman - had connected the set's RED (antenna) lead to the BNC connector. The other two screws connect to ground! The wires, being grounded to the set's chassis, had no effect as an antenna.

March 24.

I begin work on the tuner chassis by removing the RF unit and setting that aside, and then tackling the IF - expander assembly. The wires protruding from the top of these cans and going to the IF amplifier tubes were badly frayed and in need of replacement.

Here's how those IF transformers look with their shields removed:





After replacement of the wires, the shield was put back in place.



I find it easiest in these situations to feed the wire (in this case, wires, plural) from the spool of wire (again, three spools in this case) through the shield, solder the wires to their proper place(s), reinstall the shield, then cut the wires to the proper length. This cuts down (pun unintended) on wasted wire.

March 25.

By now I have about half of the tuner chassis recapped (the right side and a couple on the left).



I am also replacing all of the old carbon resistors. Overkill? Maybe. But knowing how old carbon composition resistors increase in value over time, I know the radio will be happier (and perform better) with all new metalized film resistors as well as new capacitors.

Again, no restuffing of caps - you can see on the left side of the chassis that there are no original caps left to restuff.

One of the old resistors was the Micamold type, part (69), 500 ohms.

Having no 1 watt 500 ohm resistors on hand, I improvised by placing two 1000 ohm, 1 watt resistors in parallel to end up with a 500 ohm, 2 watt resistor.



Works for me...

You can see how burnt and bubbled the original Micamold resistor was in the photo above.

April 1.

By now I have the tuner chassis (except the RF unit) almost completely recapped and recarbed.

I turned my attention to the area surrounding (85), the discriminator transformer.

I have removed the interconnect cables as they need to be replaced anyway, and the absence of the power cable will help me work in this area.

Part (85) had two old 2 meg resistors protruding from its underside, and some wires that looked questionable.









I removed (85) and removed the innards from the shield - no easy task!



I replaced the red and white wires, resleeved two other wires with new black tubing, and replaced the 2 meg resistors.



I reinstalled this assembly in the shield...





...and reinstalled (85) in the tuner chassis.

April 5.

Let's rebuild part (108) - the three-section capacitor in a metal can.



Having removed this from the tuner chassis, the first thing to do is pry open the tabs which hold the insides in place.



Now, the innards easily pull out from the can.







I put together the replacements - two new 0.1 uF caps and one new 0.68 uF cap.



I put the original gray insulating paper back into the can and then put this assembly of new caps into the can. You can repot the unit with hot glue if you wish; it will hold everything in place as well as keep everything well insulated. And the hot glue does not harm these capacitors.

Don't forget to place the black insulator through which the wires protrude back in place, and fold the tabs back over.

The common (ground) lead is soldered to the outside of the can (not shown here).

The finished product, all new inside:

April 9.

Having completed the main part of the tuner chassis except for replacement of the interconnect cables, it was time to turn my attention to the part I dreaded most - the RF unit.

I have said this before - if I had my way, I would bring David Grimes back from the dead and sentence him to a lifetime of having to service the RF units of every higher end 1937 and 1938 Philco which used his awful RF units.

His invention was, in my opinion, one of the worst things Philco ever came up with. The RF units of the lower end models aren't too bad, but any RF unit with an RF amplifier stage is extremely difficult to service. Add to that the oscillator control tube as used in this radio, and you have a very complicated, very poorly thought out unit (from the perspective of the person who has to service it).

But to understand just why Philco went with Grimes' RF unit idea, we have to look at radio history in context.

RCA had developed what it called "Magic Brain". This, too, was a separate RF unit which could be removed from the main chassis for service. Unlike Philco's "Unit Construction", however, RCA's Magic Brain has wiring which terminated in a plug. Remove four screws, remove the plug, and remove the Magic Brain. Simple.

With the Philco RF unit, one must unsolder up to 12 wires - and then it can be H**l to get the RF unit pulled from the chassis.

Any mistake can seriously damage an RF unit. I damaged this one in removal. I forgot to unsolder one wire, and that cost me RF coil (14). This is why I was advertising for a coil a month or more ago.

So...I purchased an entire 38-116 chassis from the auction site just to get another RF unit so I could replace that coil.

I know...I probably should not have even mentioned it...but look, we all make mistakes.

Anyway...

Here are the two RF units side by side.





You can tell that the original 38-690 RF unit has one damaged tube shield base, and one missing. People did that so they could use metal and/or GT tubes in the Philco sets designed only for use with G (taper-top) tubes.

And notice in the second picture above - the 38-690 tuning condenser is rubber stamped 38-116.

The RF units of both radios are identical.

April 15-16.

I decided to rebuild and use the 38-116 RF unit instead of the 38-690 RF unit.

Why?

The 38-116 RF unit had unmolested tube shield bases.

I began the long, drawn-out process of removing one section of the RF unit at a time, replacing capacitors and resistors as I went. The main sub-base of the RF unit (where the tube sockets are attached) were also rewired...which took quite a bit of time.

Remembering my experience with my 37-670, I decided to replace everything...including mica caps.



I replaced the original micas with new silver micas, or with NP0 (C0G) ceramics.



In the case above, capacitor (19) was 130 pF. So I connected a 120 pF and a 10 pF in parallel to obtain 130 pF.

When this section (the middle section) was finished, here's how it looked:





Now have a look at the oscillator section of the RF unit before I did anything to it.











Coil (37) was bad. Notice the greenies in the middle:



I checked the same coil in the 38-690 RF unit and, fortunately, it had good continuity! So I carefully removed it from the 690 RF unit and installed it in the 116 RF unit.



While I was working on the RF units the evening of April 16 (my birthday), Debbie provided a very pleasant interruption:



H B 2 Me!