[sjhs1962]

I am curious about wire size for rewinding rf coils. It seems that the primary wire size is smaller....e.g. #38 vs. the secondary wire around #32 awg. This seems counterintuitive and I was wondering why. What is the principle involved here? I presume it is not a' step up or step down ' relationship, or is it??? And sometimes it appears that the wires are the same size for both primary and secondary sections.

[exray]

IMO, its more a matter of fitting the turns on a reasonably sized form. I had to rewind one (BCB) recently in a 30s era radio and it seemed like the original was around 34-36ga. All I had was 30 and 38. 30 wouldn't fit but it did turn out ok with 38 although I had to tweak it quite a bit with my AADE L/C meter. There was 15-20 turns of difference.

The problem in doing like I did going from 34 to 38 was there's a difference in the distributed capacitance. So although the inductance came out ok, it didn't track as well as the original.

Using 38 when you can do the job on the smaller secondary with 32 simply introduces more production issues.

[sjhs1962]

Exray: gracias...my project is an Audiola 31 TRF. I have been trying to get info. on rf coils. A couple of questions: how successful is coil rewinding in general, without the sophisticated equipment you seem to have? When you tweak it, does that mean adding extra wraps or removing them? How is that done...since you almost have to hook everything up for test....I mean is there an easy way to do this without a total redo? Can you tell if primary is not correct enough? Any tips greatly appreciated.

[murf]

IMO, its more a matter of fitting the turns on a reasonably sized form. I had to rewind one (BCB) recently in a 30s era radio and it seemed like the original was around 34-36ga. All I had was 30 and 38. 30 wouldn't fit but it did turn out ok with 38 although I had to tweak it quite a bit with my AADE L/C meter. There was 15-20 turns of difference.

The problem in doing like I did going from 34 to 38 was there's a difference in the distributed capacitance. So although the inductance came out ok, it didn't track as well as the original.

Using 38 when you can do the job on the smaller secondary with 32 simply introduces more production issues.

Anyone interested in fixing an antenna coil out of a Philco model 76?
I am too chicken to attempt this,and can't seem to find a replacement.
Thanks, Murf

[exray]

Exray: gracias...my project is an Audiola 31 TRF. I have been trying to get info. on rf coils. A couple of questions: how successful is coil rewinding in general, without the sophisticated equipment you seem to have? When you tweak it, does that mean adding extra wraps or removing them? How is that done...since you almost have to hook everything up for test....I mean is there an easy way to do this without a total redo? Can you tell if primary is not correct enough? Any tips greatly appreciated.

Hi, yes, I have seen your posts on the other forum.
If you use the same gauge of wire, and the same number of turns, and fill up the same coil length then your rewound coil should be no different than the original. Of course that is easier said than done. If you try to bump up/down the wire gauge by even one step it becomes 'interesting' and will require some tweaking adjustment.

As I recall, yours was a multi-stage TRF set. (Three stages? ) Now, with a single stage circuit like a crystal radio or regen radio (or a simple RF coil in a Philco) you can wiggle around at will but when all three stages need to complement each other then precision is needed. The older Three-Dialers were built that way just for that reason, the operator had control of the tuning of each stage. But when they are ganged together by a common tuning capacitor gang...well, you can see the difficulty.

No sophisticated equipment here Just an AADE meter. I do a lot of homebrewing so for the $100 cost it serves me well and I couldn't live without it. Helps out on old radios too! But aside from plonking down 100 bucks I suggest reviewing your rewound coils to see how closely they resemble the originals if you still have the data handy. Its much easier to fork over a few dollars for the correct gauge wire if that is in question. (I ordered some 34 and 36 to have on hand after my recent quandry)

To answer your specific questions. Tweaking, yes, using the AADE meter while adding or subtracting turns. There is no reliable alternative. If it were one coil out of three you might be able to tweak it by trial and error but I recall all three of yours were open.

Primary is usually not all that critical in interstage RF transformers. You achieve resonance with the larger secondary (grid circuit). The turns ratio relationship should remain the same regardless of the wire size (more or less).

Hope this helps.

[sjhs1962]

Exray....thanks and yes your posts help and all advice helps. I have ordered some wire and have setup a rudimentary rewinding apparatus. So I will give it my best shot. I am hopeful to hear a station and will proclaim it a great success. I will let you know.