[tym]

Hello everyone. I have been restoring my Philco 19B and documenting on ARF.

I've been chasing down an intermittent and challenging issue with periodic and temporary volume drops. I finally found the likely cause today, an open antenna transformer primary in which the broken wire was making intermittent contact to the outside of the coil. The coil looks to be charred from lightning damage.

The entire transformer is part number 32-1062.

I am considering rewinding the primary or replacing with a compatible substitute. Does anyone know how many turns the primary should have? I do have 40 AWG magnet wire left over from raining the shadow meter coil.

Thanks!

[Radioroslyn]

I rewound one of those a while back. Used about 40' of 40ga wire. It's not particularly critical as it's just used to couple the rf signal from the ant to the tuned circuit of the rf stage. It doesn't affect the tracking. The trick is getting the cardboard strip out of the coil form w/o breaking it...

[tym]

Thanks, so it sounds like a scramble wind that fills the bobbin the same amount should do it, without having to duplicate the turns count?

I will wind in the same direction as original and connect inner and outer ends of the winding to the same terminals.

[tym]

Using a tip from Ron's blog (RIP), I was able to pop out one of the cardboard tabs and remove the crispy primary coil. Nicely charred.

[morzh]

Use it as a spice.

Old spice.

[tym]

Let the spice flow...

The original wire was too friable for me to be able to count turns. Since that's not a critical parameter anyway, I'll just scramble wind roughly the same amount of wire onto the bobbin in the same direction as the original.

[David]

Looking on Nostalgia air at the model 19 gives a ohm value for the ant coil. If you know the size of the wire can figure length. I always add a few extra turns I can always remove extra wire if needed.  http://www.nostalgiaair.org/Resources/151/M0013151.htm

[tym]

Thanks. Looking it up online, AWG 40 wire is about 1.05 ohms per foot at room temperature.

[tym]

I completed the rewind with AWG 40 wire.

The Nostalgia Air link notes the primary should be 27 ohms. Ron's (deactivated) blog suggests the original may have been AWG 38, which is about 0.66 ohms per foot at room temperature.

My rewound coil measures 85 ohms, so I may have overdone it a little and put on ~80 feet of wire when the original likely used closer to 40-45 feet. I've coated the coil with wax already to keep the fine wire in place, so can't easily remove turns.

Any reason not to just use this as-is?

Photos of my poor-man's coil winder and the final product attached.

[GarySP]

Given the choices, I'd rather have too much wire problem rather than not enough. Try it as-is ... If it needs finer tuning, just unwind a little until you find the spot!
Regarding your "poor man's" coil winder ... Absolutely brilliant! Functionality without incurred cost ... all good!
Take care and BE HEALTHY! Gary

[David]

Living in the South we would call your coil winder great redneck engineering. In your parts Yankee ingenuity. I like it! David

[tym]

Thanks, Gary and David! Makes sense - and hard to believe it will be any worse than the zero-turn coil it had previously...LOL

I used a wine bottle cork from the top to pop the primary coil assembly back into the slots of the secondary's coil former. I then used some drops of molten wax to "glue" the tabs into the slots like original.

All windings still have continuity, so at least I didn't break anything. I won't have time to reinstall the transformer until the weekend. Fingers crossed!

[tym]

The repaired transformer is reinstalled and the radio is working well - no sudden and intermittent volume drops (which prompted this repair effort) and improved sensitivity on both bands. So, more proof that the turns ratio in this applicaton is not critical.

I measured the gauge of a piece of wire from the original coil. It had some solder on it which made it hard to get an accurate diameter measurement, but it does seem to be somewhere between AWG 36 and 38, for what it's worth.

[tym]

So as if to taunt me, shortly after typing the above post, I had another volume drop issue. I checked the second RF and oscillator transformers - all windings are good including the pesky tickler coil. I had already reduced the 15k resistor in the oscillator circuit to 10k and replaced the 700 pf cap in the bakelite block with 750 pf (three 250 pf silver micas in parallel).

I did two things to try to resolve the issue (not the best approach to diagnose an issue, but I was getting a bit annoyed).
-Swapped in another 36 tube in case it was an oscillator issue (doesn't seem to be the case as I can still hear stations).
-I noticed the rivet for the antenna Fahnestock clip was a little loose. I warmed up the gun and soldered both sides of the rivet (above and below the chassis) to ensure a good connection.

In earlier stages of the restoration, the volume control was replaced with a correct tapped unit from Mark Oppat and the tone control and bandswitch were thoroughly cleaned.

Anything that I am missing?

[tym]

I played the set for 2.5 hours without any problems. I have now put the original 36 tube back in (after reflowing the solder on the top cap a second time) and will retest.

EDIT: I tested another 3+ hours with the original 36 tube and the only change in volume was when the station I was listening to reduced power at sunset.

Phew! It might finally be fixed!