[Ron Ramirez]

Well...youse guys are just better than I am at those 1937-38 coils!

[morzh]

I do mine by hand. 16 to 40 turns.....no biggie.

[Phlogiston]

not that I don't love coil winders - -

[morzh]

Oh I love'em. I just don't have'em.

[rfeenstra]

This certainly is doable by hand, but the winder was sitting there so I used it. I've got one hand that doesn't always cooperate and I can see me dropping the coil half way through! I've done several output transformers on this thing.  Couldn't do that by hand!

[rfeenstra]

Russ, you mentioned that you did/do not use  the separator between the primary and secondary.  Does that work in all cases or just when you use new wire for both primary and secondary?  No doubt that the modern enamel insulation is much better than the old stuff.  I used a separator cuz the original did.  Off course the original caused the problems in the first place. You can see one of the green spots in this photo.  I used tape as the separator hoping that the adhesive would not cause a problem down the line.  To help against that  and to hold the wires in place, bees wax was melted over the windings before the tape was applied.  I'm also counting on today's insulation materials to be more immune from chemical attack.

     

[Phlogiston]

It is because of the new enamel. If there were a considerable voltage difference, but there is none here. Layering in output and power transformers is more of a concern, but still, the voltage difference between subsequent layers is still not enough to break-down the coating.

P.S. I have used stretch-wrap between layers on output trans - more to hold layers in place than to insulate. We'll have to see how that lasts, but I am confident that it will outlast me.

I just found this picture that I titled "Worst Cap" from a 37-116:

   

--looks like a bank of RF coils rather than the osc bank.

[Ron Ramirez]

...precisely why I've previously said that David Grimes should have been sentenced to a lifetime of having to repair/re-cap those things (his RF units).

[morzh]

Well, some of RF transformers are used with the primary being at the plate potential ()anywhere from 40V to 200V) while the secondary is at pretty much 0V. In these cases you do want some separation. Not likely but due to the enamel defects it is theoretically possible for the two windings to short.

[rfeenstra]

Good point on the voltage difference between primary and secondary on some coils.  Didn't think of that.

[Phlogiston]

Yeah, but not on those osc. coils.

[morzh]

No, not in this case.
I just thought I'd mention that since at some point the conversation came to just RF coils. Which could be anywhere.

[rfeenstra]

To change the direction of this thread just a bit, since this is the first "HI-FI" AM radio I've had experience with, I decided to play with the  selectivity control a bit.  I fed the radio a modulated RF signal to the antenna terminal and varied the modulation frequency from 30 Hz to 10K Hz.  With the selectivity control in the fully clockwise position (narrow band width), anything above 5kHz was highly attenuated.  In the counter clockwise position, 8kHz was attenuated but still significant on the scope connected to the voice coil.  My ears are getting old, I know, but I couldn't hear much above 7.5kHz.  I don't think the speaker is capable of it.  I kind of wish Philco had separated the Treble control from the selectivity control.  It would have given better control over the intensity of the high frequencies.

For fun, I did the same thing with my Scott 16A from 1947.  It's speaker is a coaxial and has a little better high frequency response.  Interestingly, even a 10kHz signal is significant on the scope, yet selectivity is good.  I can hear the the sign wave to above 8kHz., which is probably where my ears drop off.  Evidently, they learned how to give a wide AM frequency response and still maintain a degree of selectivity.  Perhaps this is why the "HI-FI" AM sets kind of disappeared after '38, '39????  Or was it the prospect of FM coming soon?

I am enjoying playing with this radio as it sounds good and is quite sensitive.  The automatic tuning and Magnetic tuning work well.  Bass response is excellent and well balanced.  Perhaps the passive radiators (acoustic clarifiers) have something to do with that.  This has been a fun experience and all of your input and comments have been a great part of it.  Thank you!!!

[rfeenstra]

Well crap!!  Was listening to the radio and it was and has been playing fantastic.  All of a sudden there was a bunch of static, and then a station that spread itself from 1300 to 1600 was audible. I was listening to my home transmitter set a 1500. Changing the frequency of the home transmitter I was using brought in different stations.  Interesting!  With the transmitter set at 1470, I had a station that actually transmitted on 1000.  The difference is the IF frequency so I concluded the oscillator died.  Sure enough, the tube was dark.  Put in another 6A8G and part of the dial started to work.  Other parts of the dial were dead. Slowly, dead parts of the dial came to life. After about 10 minutes, the whole dial worked but other bands had problems. The oscillator seems to be a bit temperamental.  This is not good as this is in the tuner assembly which is a b..ch to get at.  Most of the resistors were nicely within spec so they were not changed.  I suspect I have a resistor that has drifted high with use.  Why it all happened at the same time, I'm not sure.  Interestingly, the dark tube will still get warm even though the filament is not lit.  Something in the tube is drawing enough current to generate a bit of heat.  Maybe this damaged something in the circuit.  I'll check voltages once I get the radio out again and on the bench.  I'll let you know what I find!