Hallicrafters S-40B Antenna Coil rewind

[ns7h]

Any folks out there have an old S-40B receiver and have had to rewind the Band 2 coil(s)?  The coil is L3 and is connected through the bandswitch to the antenna.  I restored this receiver a number of years ago, forgot about the issue on 75 meters (weaker signals on Band 2).  Evidently in an earlier life for this receiver someone fried the input by too much RF and tried to fix with a different external RF coil.  The original unit still has about 3 ohms continuity but does not peak with the associated trimmer capacitor.

I rewound an antenna coil for an HQ170 for the same reason (I was a new ham in 1963- fried it myself!).  Other than a lot of patience (maybe on a good day), good eyes (I am 75), and steady hands (did I say I was 75?), is there any wisdom out there for the task??

NS7H

[DMOD]

I think I would also be suspect of the associated trimmer capacitor.

[AJ1G]

If you suspect the coil primary (input/antenna) side is suspect, I would try to discern the turns count on it and check it’s continuity with it isolated (by disconnecting) any associated trimmer cap.  If it’s fried open, you might be able to remove the remains of primary and lay on a new primary winding. Also visually and with an ohmmeter check any associated trimmer cap for shorts.  Don’t overlook the possibility of burnt bandswitch contacts.

One of the first radio troubleshooting and repairs I performed on a radio was this exact problem on my E. H. Scott SLRM receiver.  Band 3 that covered 80 and 40 meters was suddenly very deaf, found the antenna coil primary wide open, probably from a lightning near miss.  Just laid on a new primary winding over the old one.  Still in there 57 years later!

[W1RKW]

although not a radio but a similar concept, back when I was a poor college student, my car had a check engine light.  After much time troubleshooting, I narrowed the problem to an open coil on a solenoid valve in the emission control system.  A new valve was cost prohibitive at the time so I figured first I'll dissect the solenoid. Had nothing to lose. Casing was injection molded so proceeded to carefully remove the casing. Once the coil was exposed, I looked it over carefully. It was indeed open and probably open within the winding somewhere. So off came the winding which was easy. Now the hard part, rewinding the solenoid coil.  The coil wire was very very thin, hair thin and thousands of turns needed. Hair thin breaks easily so winding by hand might be tricky. Tried that a couple of times by hand and I didn't have the patience to do it.  I needed a nice neat and consistent rewind so I built a simple coil winder.  I didn't worry to much about turns count since it was a solenoid. I just refilled the bobbin to a similar amount, eyeballed it.  More critical for a radio coil but not this. Anyway, check engine light went out. I was happy and saved some $$.  So I say rewind it. take your time.  you can put more turns on the bobbin and if too much, easily remove some turns. that's easier than having to add turns.

[ns7h]

Well guys, thanks for the response.  I took the coward's way out and found an operable coil/trimmer unit in a parts S-40B.  When I took the damaged coil out of the receiver, a whole section was missing (three sections in the unit) and an external slug tuned coil was connected/jumpered and the trimmer was not connected.  As in the earlier note, the likely fault was a failure for a TR relay to operate.  The evidence was a tell tale blast pattern above the coil on the chassis.  I had no clue about the missing section until I got the identical component from the parts rig.  No data on the coils of course, so rewinding would be an excessive challenge to my patience, eyesight, and mental stability (did I say I was 75?).

The parts rig surrendered a good looking unit, fit well, and works like a new receiver on band 2.

Thanks for the forum again.

NS7H