Model 70 Detector Coil/Transformer - Printable Version
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Model 70 Detector Coil/Transformer - jjfritz5528 - 08-15-2023
This is my first attempt at fixing this, so go easy on me!
The Primary winding is open, and according to the schematic it is Part# 03083. one of the wires was broken near the solder terminal, but there must be another, or more breaks elsewhere. So I plan to rewind the primary.
I found in the Library the "Rewinding Philco Coils" information, which is a big help, but I want to confirm some information.
The links to the www.philcorepairbench.com don't appear to work, and I tried going directly there, and no luck either. It looks like there should be 69 turns of #32AWG for the primary. I can try to count the turns when I remove the existing winding to confirm. It looks like there are 2 layers of windings for the Primary. If so, I think there are more than 69 turns, but I will check that and plan to use the same number of turns as the original.
I don't have any #32, but I do have #34. Would that be OK, or is it critical to use #32?
Anything else I need to be aware of? I know direction of the wrap is important.
What do most people use when finished to help keep the windings in-place? I think it used a wax originally.
Thanks in advance!
RE: Model 70 Detector Coil/Transformer - Chas - 08-15-2023
Use the same size wire.
I have rewound using my methods and got a good coil. But methods by others may be just as well.
Do, map the coil form to paper so you can stop at any time for a break and continue later.
I used heated beeswax, melts higher temperature than paraffin. I also coated the bare form with a thin layer of bees wax as it is tacky, paraffin is slippery. I used a thin layer of PETE plastic to replace the decomposed celluloid liner.
GL
Chas
RE: Model 70 Detector Coil/Transformer - jjfritz5528 - 08-15-2023
Thanks Chas! Appreciate the tips!
RE: Model 70 Detector Coil/Transformer - jjfritz5528 - 09-11-2023
Just got back to preparing for the winding of the Primary for the 1st Detector Coil for the Model 70, P/N 03083. The information from the website in the Coil Winding Section is for the RF Coil, so it's NOT the same for the Detector. As close as I can tell, the Primary Detector Coil is #40AWG (~3 mil, as close as my caliper reads). Could be #41AWG, but that seems like an odd value. SO I also expect the 69 Turns to be incorrect also. I haven't unwound it yet to verify, but it looks like its more turns.
I can't work backwards using the resistance to confirm the gauge, since there are obviously breaks within the existing windings. And there is no data that I found on the resistance of the Primary Winding on this transformer.
Does anyone have information to confirm the correct wire size for the Primary coil, before I order the wire? OR am I splitting hairs and just go with the #40AWG?
Thanks in advance!
John
RE: Model 70 Detector Coil/Transformer - Chas - 09-11-2023
I do not have the wire size, however, if an end of the primary can be extracted at either solder lug it can be measured. Better off getting the correct wire size in event turns count fails. But using a magnifying glass and a wooden stylus the count can be correctly made. Do replace the celluloid liner, PEET or PETE is fine and can be salvaged from a bottle or bought on eBay. Measure the thickness of the celluloid for the nearest value of PEET. I have also used acetate salvaged from a wrap of a lampshade protection. Rotting of the celluloid is a principle cause of the coil failure.
If the wire size seems to be slightly smaller than a known size that can be accounted for as the wire was wound under tension. Do allow .0005 for enamel
You will find cleaning the form thoroughly then dunking into hot bees wax until bubbling stops and the form is HOT there will be a thin film of wax. The wax will grip the wire during winding and help create a more even lay.
Confirmation of the turns can be made by multiplying the wire sized by the distance the winding occupies...
GL
Chas
RE: Model 70 Detector Coil/Transformer - jjfritz5528 - 09-11-2023
Thanks Chas!
I do have access to each end of the winding, but no continuity. After I unwind it, I can check the resistance, of the pieces, hopefully not many, and also hoping I don't lose count of the number of windings.
The caliper I have is pretty accurate, and I also have a table that shows the wire diameter with AND without the enamel coating. I have been getting my magnet wire from Remington Industries. Quick delivery and no shipping fees!
How do you attach the PETE prior to dipping in the beeswax? Would a smooth adhesive tape work?
I have to get some beeswax.
I was hoping to do the unwind and rewind all about the same time, but it sounds like I need to go slower with this and unwind to determine the correct wire, order it and then apply the Liner, dip and rewind.
A wealth of knowledge Chas!
RE: Model 70 Detector Coil/Transformer - Radioroslyn - 09-11-2023
Another way to determine the # of turns is if you still have the wire measure the total length.
And then use the dia of the coil form and Pi to calculate it.
RE: Model 70 Detector Coil/Transformer - Steve Davis - 09-11-2023
By expanding the photo, you can count the turns, I get 67.
Steve
RE: Model 70 Detector Coil/Transformer - jjfritz5528 - 11-17-2023
Additional request.
I have a defective Detector Transformer with an open Primary. The Philco website, under Techniques say the RF Transformer Primary should be 69 Turns of #32AWG.
On My Detector, I agree with the 69 turns, but the wire is much smaller, maybe #38 or #39AWG. I can't verify because I couldn't get more than 12" of continuous wire on the defective winding, it was so brittle.
The schematics do not list resistance for any of the windings on this Model. I haven't gotten to the Oscillator Coil, but highly anticipate the small outer winding will also be open.
Does anyone have information on what Gauge wire, or resistance for the Detector and Oscillator Coils should be?
My Caliper isn't real accurate at these small diameters, but #38 seems to be about right, and I have that, don't have #39 or #40AWG.
The Philco Part#'s are 03083 & 03084.
Thanks in advance for any assistance!
RE: Model 70 Detector Coil/Transformer - morzh - 11-17-2023
I use fabric glue to hold turns together in 1-layer RF coils.
RE: Model 70 Detector Coil/Transformer - Radioroslyn - 11-19-2023
So Mike is water the enemy of Q?
RE: Model 70 Detector Coil/Transformer - morzh - 11-19-2023
H2O mixed with C2H5OH is the enemy of IQ. That I do know.