[younggene]

Picking up from where I left off with the Model 38 oscillator coil problem; Twelve turns were wound onto the oscillator coil at the bottom of the resonant winding and the oscillator started working. Oscillates over entire range. Had very weak signal from antenna terminal and found the primary of the antenna coil open. Removed the old winding and wound 12 turns (no. 32) on and was able to get improved signal from the antenna terminal.

Now I want to align the oscillator and antenna coil. My problem is that I had to replace the tuning capacitor scale and now I don't know whether the scale should be balanced with the range of the tuning capacitor or whether I do something like open the the tuning capacitor fully and set the end of the scale with the full open capacitor.

The above may not be very clear but what I want to do is set the scale reading accurately with the tuning capacitor location.

Can anyone provide me with the procedure?

Gene, K4ZQM

[Arran]

 if the primaries of each coil were rewound properly, with the correct number of turns with the correct gauge of wire in the same direction as the originals, then there shouldn't be any reason why you couldn't get it to track properly. I think that the dial scale should be lined up with the pointer at the bottom end of the dial, plates in tuning condenser fully meshed, the top end is a little trickier to figure out sometimes. I'm not sure about the model 38 but most radios have a trimmer capacitor for the upper end of the dial and a padder capacitor for the lower end, although some will substitute a tunable slug inside the oscillator coil for one of them, but not in this case. Once the IF cans are aligned properly setting up the oscillator should not be too difficult if the factory procedure is followed, there is usually a lot of adjustment built into the oscillator tank circuit to make everything track properly, unless the dial scale is wrong or installed really far off which would be pretty obvious.
Regards
Arran

[Radioroslyn]

Hi Gene and welcome,
Gosh all these years I though Huntsville had electricity but I guess I was wrong!
Glad to hear you got it working, I had no doubts you could getter done.
Don't think the primary have much if any effect on the resonant frequency of the
secondary alignment should be pretty straight forward.
GL
Terry

[younggene]

Hi Terry, One would think that a city that could build rockets that send people to the moon would certainly have electrical power. A couple of years back I designed, assembled, tested at my house and helped install a 1KW solar pwr system for a friend with a cabin in the mountains, 40 miles from Huntsville. It's still working for him. I didn't ask for pay and didn't receive any. I felt he would compensate me in some way to some extent. (Oh well) I worked with solar power systems for orbital payloads for NASA here in Huntsville.

A friend inherited the Philco 38. He's an electrical engineer but with essentially no vintage tube radio experience. He realized that it was a battery set and asked if it was worth building a battery eliminator. I suggested that if all the tubes were good, then it would not be much effort to build a battery eliminator. In the late 40s and early 50s I would occasionally see an old battery radio. I remember the large plate (90V) and filament (1.5V) battery. I saw many with all tube filaments blown where the 90V had been shorted to the filament supply wire. This radio requires 135, 67.5, 7, 3, and 2 volts.

This story is getting long so I'll just say I got hooked with the whole job; building the pwr supply and making the radio play. It's like the mountain solar power system all over again!

Now to the problem at hand. Per Arran's comment, aligning the marker at the low end of the dial scale with the pointer light and the tuning capacitor fully meshed appears to be be the proper method for placing the dial scale assembly on the capacitor shaft. The oscillator can be made to track. Thanks Arran.

With the oscillator tracking, the radio still had very poor sensitivity. Better reception was had from a signal placed on the control grid of the oscillator-mixer than on the antenna terminal. I checked the antenna coil and found an open primary. As a result of corrosion, it was open in 2-3 places. I had no 38G wire so I rewound 12-13 turns with the smallest wire size I have; #32. I placed the antenna terminal side of the primary winding next to the low side of the secondary. I am getting coupling but the signal from the antenna terminal is still not as strong as when coupled directly into the top grid of the mixer-oscillator tube.

I have gone through the recommended alignment process.

I have #38 wire coming. I need suggestions and comments on how many turns, placement, hints etc.

Gene, K4ZQM

[Radioroslyn]

Hi Gene,
So your a rocket scientist!!!
I'm just a wiseguy!
I would reverse the connection on the ant primary. The diagram shows the top of the winding going to the ant post. Would also add some more turns say 25 total. Should be near the bottom of the secondary. You could add some C between the top of the pri and secondary like 10-50 mmfd.

Gl
Terry

[younggene]

Hi Gene,
So your a rocket scientist!!!
I'm just a wiseguy!
I would reverse the connection on the ant primary. The diagram shows the top of the winding going to the ant post. Would also add some more turns say 25 total. Should be near the bottom of the secondary. You could add some C between the top of the pri and secondary like 10-50 mmfd.

Gl
Terry

Thanks Terry. You promoted me. I never considered myself a scientist; more like a wiseguy. I did enjoy my 35 years of employment.

I didn't say it very well but I did connect the top of the primary winding to the ant terminal. The top of the primary winding is next to the bottom of the secondary. I'll wind it in the same direction and put on as many turns as I can without overlapping. I doubt if I can put 25 turns on there but we'll see. A few mmf across the ant tuning capacitor should help.

Thanks again Terry. I look forward for to getting email that says I have a reply from the forum.

Take care,  Gene in Alabama