[Ron Ramirez]

April 21.

I decided to gather up some replacement tube shield bases to replace those which were missing from the tuner chassis.

I had several, but they all had varying degrees of rust.

Upon Bob Andersen's recommendation of Evapo-Rust back in 2013, I bought a gallon of the stuff last year. Now I had a good reason to try it out.

It worked very well indeed:

[Image: http://www.philcoradio.com/images/phorum...90_052.jpg]

I will be using the 1937 shield bases. This way, any future owner may easily use any type of tube in the sockets - G, GT, or metal.

[morzh]

The RF units of 38-116 and 38-690 are the same, right?


690 is a lot, lot of work and headaches. If it weren't for the teansformer fiasco with Heyboer it would take me 3 months, but with it it took me over half a year.

Speaking of......although thinking of it, yours was receiving so your transformers might be ok. I'd still check them as with half pushpull it will still work and even sound ok.

[Ron Ramirez]

May 6.

It's the Sunday before Kutztown.

I need to replace the interconnect cables.

Why?

One of them feeds into the chassis with no strain relief...no clamp...no grommet. And the chassis had cut into the wires, leaving bare spots.

The other interconnect cable uses a clamp to hold the cable in place, oddly enough. But the wires of that cable looked to be rather dried out.

So, using a micrometer, about a month previously I had carefully measured the individual wires of the interconnect cable with the 10-pin connector (power leads). The four filament wires (two pair; one red, the other black) were both 14 gauge.

The wires for the power switch were 16 gauge.

The other wires were 20 gauge.

Cloth-covered wire I had on hand already could be used to replace the 20 gauge wires. But I had to purchase 14 and 16 gauge wires for the job.

These were found at a place I had never heard of, which sells cloth-covered wires for the vintage automotive crowd - Tom's Engine Barn.

They filled my order in a reasonable amount of time and soon, I had all of the wires I needed for the 10-conductor cable.

I also had to order a two-conductor cable with shield for the other interconnect cable (the audio cable). This I purchased from Mouser.

[Image: http://www.philcoradio.com/images/phorum...90_067.jpg]

After some twisting of wires...

[Image: http://www.philcoradio.com/images/phorum...90_068.jpg]

[Image: http://www.philcoradio.com/images/phorum...90_069.jpg]

Both cables also received an outer braided covering purchased from Antique Electronic Supply. It's plastic rather than cloth, but it looks good.

Once the cables had been made and slipped into the braided coverings, I attached the individual wires inside the tuner chassis.

For the audio cable, which has no clamp or strain relief (and never did), I put a rubber grommet into the hole before passing the cable through the hole, to help protect the wires from what had happened to the original wires.

[Ron Ramirez]

Also May 6.

I've finished recapping and recarbing. Under the chassis, things now look like this:

[Image: http://www.philcoradio.com/images/phorum...90_071.jpg]

You may recall that I had mentioned earlier that I needed to pass a wire through a rivet hole for the 1st audio (6R7G) tube. With many thanks to Ed Locker for the idea, I used a 3/16" aluminum pop rivet to attach the tube shield base and tube socket to the chassis. I then used a nail to drive the aluminum nail out of one of the pop rivets. A new cloth-covered wire then fit through the rivet perfectly.

[Image: http://www.philcoradio.com/images/phorum...90_070.jpg]

[Ron Ramirez]

Also May 6.

I carried both tuner and amp chassis back upstairs (one at a time, naturally) and put both chassis back into the cabinet, where the speakers were still attached.

I hooked everything up through a Variac and slowly applied power.

The set came on...nothing bad happened...but...

NOTHING.

The only thing I could hear was The Sounds of Silence.

Only when I rotated the band switch knob I could hear static, but other than that...nothing.



So...I decided to go try and enjoy Kutztown and forget about this project for awhile.

[Ron Ramirez]

May 11.

At Kutztown, I ran into an old friend whom I had not seen for several years...fellow radio collector Dr. Mike Schwartzman.

He and his brother Dr. Dan were both there and it was great to see both of them. I had seen Dan at a recent Kutztown event, but as I said, it had been several years since I had seen Mike so it was great to have a little time to catch up with him.

As luck would have it, Mike had brought a 38-116 chassis. He very kindly gave it to me. I can't say how much I appreciated this very kind gift, especially since I had a feeling I was going to need yet another RF unit for this 38-690 project.

Steve (azenithnut on ARF and theradiofox here) had mentioned that he was needing the shaft for the IF-expander assembly for a 38-116. I only needed the RF unit from Mike's chassis, so I removed the RF unit on the spot and re-gifted the remainder of the chassis to Steve.

[Ron Ramirez]

May 20.

I had promised myself to not touch this 38-690 again until June.

But I had to know...was the fault in the RF unit as I suspected, or somewhere else within the radio?

So...I set the whole thing up (both chassis, woofer, and both tweeters) on the workbench and tried it out.

[Image: http://www.philcoradio.com/images/phorum...90_072.jpg]

With the 690 set to band 1 (AM), I fed a 470 kc IF signal into the grid cap of the mixer tube.

Guess what...the signal came through loud and clear.

While removing the signal generator lead from the grid cap of the mixer tube, I happened to notice that when I touched that grid cap with my finger...I started hearing AM noise!

So I connected a temporary antenna to the mixer grid cap and found that I could easily tune in my home AM transmitter (but nothing else on AM). I was also picking up some faint signals on one of the SW bands - Band 3 or 4, I think.

A-HA! I was right - there was a problem in the RF unit!

Hear the 690 for yourself, receiving my AM transmitter with a wire connected to the mixer tube grid:

[Video: https://youtu.be/d8fBMWCy7-U]

So...while I had the thing up and running, I went ahead and aligned the IF strip.

My next job is to remove that RF unit (again). Here some of you may disagree with my plans - that's okay, as Rev. Mason used to say, you have every right to be wrong if you want to be.

I am going to rebuild the RF unit I obtained from Mike Schwartzman and see if it performs any better.

Oh, and by the way, are the 38-116 Code 125 and 38-690 Code 125 RF units identical? As I mentioned in post #14, page 1, this thread:

The RF units of both radios are identical.

I will recheck the audio interstage transformer as well as the audio output transformer. Both showed good continuity when I rebuilt the amp chassis, but it will not hurt anything to recheck.

[Ron Ramirez]

A slight clarification:

The 38-116 Code 125 RF unit has no connection at contact C10 of the multiple wafer band switch assembly, but the terminal is there. The 38-116 does not have a separate bass amplifier circuit, so there is no bass amp to short out in the four SW positions.

The 38-690 Code 125 RF unit has a wire connected from contact C10 to the bass control and one of the control grids of the 6N7G 2nd audio tube. This permits the bass amp to only operate in the AM position - the bass amp is shorted out in the four SW positions.

Otherwise both RF units are indeed identical in every aspect.

One more thing. For any of you who are inclined to follow the bouncing resistor symbol, I previously posted the entire package of 38-690 service info here.

[Ron Ramirez]

May 25-26.

I begin taking apart my third RF unit.

The RF tube socket will need to be replaced to avoid a potential carbon track - part of the Bakelite is broken away on the bottom side.

I will also have to rewire the sub-base as the original wiring doesn't look the best.

By this evening, I had the antenna unit redone:

[Image: http://www.philcoradio.com/images/phorum...90_073.jpg]

and the RF unit:

[Image: http://www.philcoradio.com/images/phorum...90_074.jpg]

All of the coils in these two units have good continuity...but from prior experience not just with this Philco, but other 1937-38 Philcos as well, I know that that alone does not always equal proper performance from all bands. I'll need to clean the heck out of the band switch contacts, however, to (hopefully) avoid the same issues I had with the second RF unit.

[Ron Ramirez]

May 27.

If anyone is still reading...

Only the oscillator unit remains, along with the sub-base.

[Image: http://www.philcoradio.com/images/phorum...90_075.jpg]

[Image: http://www.philcoradio.com/images/phorum...90_076.jpg]

[Image: http://www.philcoradio.com/images/phorum...90_077.jpg]

You can tell from these photos why I am replacing the wiring.

I removed the oscillator section from the sub-base and began replacing all of the wires.

By the time I quit tonight, this is how it looked:

[Image: http://www.philcoradio.com/images/phorum...90_078.jpg]

Almost finished. I need to replace the RF tube socket, a couple more wires, and a component or two. Then I will examine the actual oscillator unit, make sure the coils are good, then replace some wires in the actual oscillator unit before I start putting it all back together again.

[Arran]

Ron;
  I found this one that same site you linked to, it's not the same as the original Philco stuff but at least it looks like it's from the era, asphalt wire loom:

https://enginebarn.myshopify.com/collect...e-loom-1-2

I've heard of people striping out bungie cords and some types of rope to get an old cloth style looking loom but this might be better. Of course there is the ready made cables that AES sells, they used to call it Atwater Kent power cable, but it probably has wires of the wrong gauge for thinks like the 690s.
Also thanks for that link, I don't think that they are really and antique car restoration supplier, I think that they are more for the stationary engine restoring crowd, though you could use their materials and parts on really antique cars too, or 1920s battery radios for that matter. I like the fact that they also have cloth wire with tracers much like the stuff the original 690 cable has, that's a little more difficult to find then the plain coloured stuff.
Regards
Arran

[WyTex]

Hi Ron

Is what you're discovering in that 690 normal age related issues or is this unusually worn in many areas?

Do the issues relate to over use or years of neglect? I'd imagine it depends how it was stored as well.

Thanks
Paul

[Ron Ramirez]

Arran

Oh, I didn't even notice the cloth loom when I was on the Tom's Engine Barn site! Only, 1/2" would have been too small for both interconnect cables. Well, I *might* have been able to get the audio cables into that loom (it may have been a tight fit though), but not the power cables.

I don't think that they are really and antique car restoration supplier, I think that they are more for the stationary engine restoring crowd

I think you're right. But nevertheless, their prices on heavy gauge cloth covered wire was less than other suppliers I found. And the wire is excellent quality too, the insulation is thicker than the insulation on the original Philco wires so it should easily last another 80 years.

[Ron Ramirez]

Paul

The radio is, after all, 80 years old. I'm starting to see more of this heat and age-related wear on old cloth covered wires than I used to see several years ago. In addition, I'm being over-the-top extra careful on this set because it deserves the extra care.

I don't think any damaged/frayed wires were due to over-use; after all, one does not fiddle with wiring while a radio is in operation.

[Ron Ramirez]

May 28.

I started the day by finishing up the sub-base:

[Image: http://www.philcoradio.com/images/phorum...90_079.jpg]

I replaced the RF tube socket, wired it up, and replaced resistor (38).

Then I turned my attention to the oscillator unit.

I checked all of the coils and was greatly dismayed to find that the band 5 primary of coil (37), which is two coils on one form and serves as oscillator coil for bands 4 and 5, was open!

However...

I then discovered, quite by accident, that one lead going to that coil was broken!

I tested for continuity again and (happily) found that the winding in question was good after all. Whew, what a relief!

So I carefully soldered a piece of wire to the little "nub" left on the coil form, the other end going to terminal E12 on the band switch.

I replaced all but a few wires on the oscillator unit, as well as resistors (33) and (43) as well as another resistor, not on the schematic but listed in one of Philco's "Changes in Models" bulletins (15K) which is connected across the band 5 oscillator coil primary.

Here's how it looks now.

[Image: http://www.philcoradio.com/images/phorum...90_080.jpg]

Now it is time to start reassembling the RF unit, a section at a time. But first I shall need to carefully clean those switch sections with DeoxIT.

Back to work tomorrow, so progress will necessarily slow to a crawl until next weekend. I don't have much spare time at all on work nights. Nevertheless, I do hope to have the RF unit finished in a day or two, install it in the 38-690 tuner chassis, and try the radio out again in the next few days.