[morzh]

I am on the fence about restoring this 38-14 I got during the last Kutztown.

http://www.nostalgiaair.org/PagesByModel...013238.pdf

I paid maybe $15 for it. A fairly durty backelite case, but the chassis is clean enough.
This will require lots of cleaning, especially the case.
No original caps, the tubulars all were replaced by the black beauties; the electrolytics are paper-cartridge axials.

Now the question: I decided to check the speaker first. The transformer is good, the cone is good, the FC is 23 kOhm. According to the sch it is 3 kOhm.
It is not open, it is 23K. I cannot imagine the failure of a wirewound coil where it does not get open, but develops 23K resistance.
The speaker seems to be original Philco; same cone assembly as in 38-12, and the FC looks the same, except the resistance value.
The coil in 38-14 is in parallel to the first rectifier cap and is not used as the filter; they have a separate choke for it. So, naturally, it is expected to be a higher resistance than in the 38-12 (3K vs 1.5K). But 23K?

So, my question is: has someone encounter this before and can 23 kOhm FC resistance be legit? If not, at this point starting this radio makes little sense for me.

PS> I thought, why not check my old idea of mounting a strong RE magnet to the centerpole and replace the FC as the magnet (it is not being utilized as the filter). Well, tomorrow is another day.

[morzh]

Well, I climbed down off of that fence and decided to proceed with restoration.
I did experiment with the speaker.
I never did that before.
I fed 10V AC (from the Isol. xfmer and Variac) to the outnput xfmer, and heard the hum.
Then I connected a 9V battery across that coil and the hum increased a bit.
Putting a Neodimium magnet inside the VC did not change the percepted loudness.

Anywho, I also found a 38-12 speaker with half cone in my stash. I might get it re-coned.
Or I might hunt down a 38-14 speaker. I have seen one listed as 38-12 one, but somehow sith the FC resistance of 2.5K, which tells me it might be 38-14 one. It is on that Play THings of the Past site, so this is why I was asking about it.


So. The radio was repaired before, and it was in 50s, because the parts (Black beauty and some other non-Philco tubulars) are mostly not original. The elctrolytics are also tubuilars: the originals were removed and discarded.
Because of that, after making sure all RF coils (other than the IF; I did not check it, never do), I decided to proceed with the restoration, but with a lighter version of it: I will be replaacing the parts directly, without trying to restuff and such. The reason is, I would have to find all original things, and I am not sure I want to do this. So, the radio will be flaunting bright yellow caps inside, should someone ever be interested enough to look there. As well as the aluminum radial Panasonic electrolytic caps.

Most resistors seem good as they are. All tubes are good and strong.
Maybe in Kutztown I might be able to get another junker with a good speaker.
Plus there is auction in Oct in my town; who knows what that might offer....

To be continued.

[morzh]

Other ailments are also present.
The lamp socket requires rebuilding as the insulation inside is all crumbling. I have done it but forgot I need a nylon washer. Will have to find one.

I have finished the recap. THis is how it looks now.

   

Also, a funny find: the 300 Ohm resistor happened to be a 27K one, measuring at 30K. Considering there is no obvious change in wiring, I wonder how it ever worked after that repair. The resistor is visible here. It is #31 in the sch below.

   







http://www.nostalgiaair.org/PagesByModel...013238.pdf

What else...all resistors are done. Now I need the speaker. For alignment I could get by a PM one (I cannot seem to locate my perm 8" speaker after that French drain disaster of a project...).

Obviously, all has to be done via an isolation xfmr, as this one is a "warm" chassis radio, the AC IN wire (I intend to make it N) separated from the chassis by 0.15uF cap, which is a true death cap.
Now I will pause a bit.

[morzh]

Strange thing about that speaker.
After I removed the transformer to try to use it with a PM speaker to align, the resistance of the FC became about 4.5K.
Then it sat awhile on the table, and the resistance increased to 6.5K.
I made an experiment: I put a 9V battery across the field coil, and then I measured the resistance, which became 4.5K again.
So I put the speaker back together and put it in the radio. It works fine.

Now about the radio.
Once the speaker was in, I powered it on and it hummed and motorboated, quite a bit.
Then I realized the shield for the 38 tube was missing. I have a spare from the sacrificial chassis, so I put it in, and the motorboating stopped, but lots of hum and noise remained.
TRhen I remembered to turn off my bench lighting, and the hum went down quite a bit.

Eventually I was able to receive one station (local), but the reception is very noisy.
I think I need to do two things:

1. Try to align it. As I use my isolation transformer, I think the Philco transformer for their generator (which they recommend) is not needed.
2. Buy a polarized AC plug. I am not comfy with the chassis being across 0.15uF cap[ from the Hot Line.
And I only have the non-pols.

Will continue....

[morzh]

I also found in the service bulletin, that in order to reduce hum modulation the 16uF cap across the rectifier tube's output is increased to 40uF. Will do that too.