restoration of a 75z receiver element for a 143/144 receiver

[Darkstar2006]

 I promised on the "trouble shooting" thread that if I decided to try to rewire one of the bad coils in a 75z receiver element i'd share it.
Ok, I am NO expert of for that matter not even a phone collector. I just have a few old phones in my house cause I like the way they ring. I'm not going to bore you with how, where or why i purchased the 75z.
Hopefully the pictures upload.
Tools and supplies
#40 copper ENAMALED magnet wire 48 feet, a small 3/4 to 1 inch thread spool to transfer the wire to, fly fishing tools (a beter quality bobbin, bobbin threader, fly vice) solder tools. 


FIRST. I needed info on the OHMs of the receiver coils. the good coil ohm out at about 43 ohms. which would be about 85 ohms for both coils. Ralph Meyer's repair book seems to confirm that. However, "G-MAN" has documentation showing 75 ohms for the same 143/144 receiver. I didn't see that post until after I completed the restoration. So I went with 85 total ohms. (a Kellogg element i have also ohm out at 85.

SECOND. diagnosis. Using a volt/ohm meter that also has a continuity setting i found which coil was bad.   

THIRD. coil removal, VERY DELICATE, each coil sits on one of the iron bars that are connected at the opposite magnet end. They are connected in series.
A. I desoldered the bad coil from its terminal connection and where it's connected to the other coil.
B. Using a Dremel cutting wheel, I gently cut the welds on the metal oval retainer cap. There are 2 oval cardboard insulators under that. Remove all and set aside. REMEMBER IT 80 TO 100 YEARS OLD
C. remove the bad wire form the insulator, AGAIN GENTLY. DO NOT TRY TO REMOVE THE INSULATON WITH THE WIRE ON IT!
D To remove the little cardboard insulator- using a no.11 exato hobby knife ,YOU ARE NOT GOING TO CUT ANYTHING, gently slide the exato between the iron bar and the insulator on the long flat side, making sure the sharp part of the blade points to the center of the iron bar. Do this on both sides. When you think its free from the iron bar gently remove it and set aside. CA glue the 2 top cardboard insulators back on. the bottom one is loose and can stay that way as long as it doesn't fall off.
FOURTH. prep the wire. using a 6ft table I painter taped one end of the wire to the table ran to the end taped it then zig-zagged taping each row until I layed out about 48 ft. I then rolled that wire on to the small spool for use in the fly fishing bobbin.
Thread the fishing bobbin 
FIFTH. re-winding the coil- attach the insulator to the fly vice by the top insulator. Start by taping about 2 inch lead to the insulator, with the end of the wire pointing to the TOP of the coil. With MIMIMAL tension on the bobbin, start winding the wire slowly from bottom to top and back, until all of the wire is on the insulator.
SIXTH. checking the continuity & ohms- You must gently scrape the enamel coating from the wire ends. First test continuity. This will tell you if you got the coating off. If you got continuity, check ohms. If too high, unwind about 1 ft per ohm, scrape, test for continuity and then ohms and repeat until you get to about 43 ohms.
SEVENTH. remount the coil
EIGTH. resolder the connections one lead to the terminal bar the other to the loose end of the other coil.
NINTH. check continuity and ohms at terminal blocks.
TENTH. place metal insulator cap on and a couple dots of solder will hold it into place
ELEVENTH. rewire and install element into shell and test the sound.


I don't know if I did it right I thought the sound was low. At least lower than the HA1 in my 151al candlestick but just about same as the Kellogg candlestick receiver that I have.

[Contempra]

I'm not expert at all , but,... wood and metal (where the wire is wound ) I guess "OHMS" wouldn't be the same thing. I imagine metal is a better conductor of current than wood. I say that, I say nothing because I am not an expert on the thing.

[Darkstar2006]

The insulator is made of some type of cardboard. So its really a oblong carboard tube with a cardboard top and bottom.

[Darkstar2006]

After re-reading my 1:30 am post, I noticed a instruction notice error (outside spelling and grammar errors). in section "Third" line "C" i said "DO NOT TRY TO REMOVE THE INSULATON WITH THE WIRE ON IT" it should have said "DO NOT TRY TO REMOVE THE INSULATOR WITH THE WIRE ON IT"
in EIGTH I should have added that "I covered the coil-to-coil solder joint with clear nail polish."
and, the HA1 receiver element , is on a 51C with a 554 subset not my 151AL.
 
finally, not sure it was worth the trouble

[poplar1]

You can modify your recent posts for a certain amount of time -- maybe 2 hours? Gives you a chance to proofread.

[Contempra]

The insulator is made of some type of cardboard. So its really a oblong carboard tube with a cardboard top and bottom.

I hadn't noticed that. Sorry .

[Darkstar2006]

You can only post 6 pictures. I did have a picture of the stripped insulator in my hand so people could see its size, but I mis-filed it. But here it is.
by the way, when I stripped the old wire off all the cloth insulation fell off. I guessed at the wire size,40, (couldn't find my micrometer)

[Darkstar2006]

Update: recently purchased another 75Z receiver element on ebay. It to ohm out at 86 ohms at the terminals. Thats just about the same (85 ohms)as stated in Ralph Meyer repair book. It has excellent sound.

[poplar1]

Update: recently purchased another 75Z receiver element on ebay. It to ohm out at 86 ohms at the terminals. Thats just about the same (85 ohms)as stated in Ralph Meyer repair book. It has excellent sound.

Is it possible that "75Z" is the impedance, rather than the model number? You are measuring resistance with a volt-ohm meter.

[TelePlay]

You can only post 6 pictures.

 . . . per reply. For 15 pictures, 3 replies would be needed.

[Darkstar2006]

Is it possible that "75Z" is the impedance, rather than the model number? You are measuring resistance with a volt-ohm meter.

Ya know I never thought of that. "G-MAN"'s document shows a 143/144 WE receiver was 75 ohms. However it doesn't say what element was in it. Neither does the info say that it is a 75Z in Ralph Meyer repair book (85 ohms resistance DC) but it seems to be backed-up by a 75Z (also about 85ohms) I purchased off of Ebay. Both, the one I purchased and the one I repaired, work well.
As I said I'm no expert of electronics or anything phone, I tried to gather as much info before I started the project. I am measuring resistance with a volt-ohm meter. An old, but pretty good MICRONTA (Radio Shack) 22-195A. I use this for a lot of toy train repairs.

... per reply, for 15 pictures, 3 replies would be needed

After re-reading my "You can only post 6 pictures" it sounded like I was complaining, I wasn't.  It was a stupid line in my post. I know pictures eat a lot of storage space and understand why the amount and size are limited. I did know that I could open another "reply" and post my mis-filed (on my computer) picture. Sorry for the confusion.