The AM Forum

I am restoring the above receiver and transmitter for a friend here in Costa Rica. The receiver didn't give much problems, but the transmitter was "worked on" before. I think that there wasn't a single trimmer cap or slug that wasn't touched and mis-aligned. The balanced mixer had other diodes and I couldn't null the carrier enough. There were various caps non original and some short circuited. A few high resistor values way off. etc, all quite common and simple to solve problems. What gave me a bigger headache was the the coil of the antenna relay was broke. I think it is a 100 V relay from Potter and Brumfield, and I wasn't able to find one. The wire is approx. 0,05 mm, so rewinding without a machine is close to impossible. I tried but the wire broke 4 times and I gave up. So I did rewind the coil with 0,15 mm and that gave me a relay that operates at approx 6,5 Volts. Rectified the 6.3 VAC filament voltage and powered the relay with that instead of 265VDC via two 8.2 kOm resistors as original. Its a small mod, but the transmitter works again. May be a tip for high voltage relays that can't be found.
The power supply transformer has a short and pulls the fuse. Even at 12VAC instead of 115 it takes a few amps unloaded, so I have to try to find one or replace the transformer with a Hammond type that come close.
When ready I will miss the S-line, it was real fun to get them going again
Fortunately, the owner had a spare set on acceptable condition without power supply for spares, and he gave them to me for the repair. So I can do it again. But this time they will stay.   ;D  Nice stuff.

some nice work, Nico ... I am in the works for restoring an S line and putting them on am .... been thru all the published mods but found them lacking .... came up with a hybrid design with only 1 added hole in the tx power supply... gettiing enuff audio swing a bit tricky .... when it checks out I will release design info

I think that 75s1 rx would be an ideal candidate for an sdr if/det back end .... trick is how to do agc  :-\ :-\

putting on AM, interesting!!
I first want to restore to original condition. The second receiver that he gave me is also operational again, just have to improve some older bad repairs for optical reasons.
The receiver has a spot for a Q multiplier. I think I will  put a sync. detector there for AM