Central Electronics 20A on the bench

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 The time has come for this 1954 Central Electronics 20A to spend some time on the repair bench.

Central Electronics was a pioneer in commercial single sideband products, using the phasing method to generate SSB. The 20A is an SSB exciter (about 20W out) intended to drive a linear amplifier. These were quite popular back in the day, and there´s still a lot of them around. I wanted one to go with my Collins 75A4 and work some 15-20m ssb.


This one I bought from from Denmark, I'm guessing it came to europe with someone at the US airforce; the manual has a handwritten adress leading to the US air force base at Ramstein, Germany.  

This transmitter needs some work before I can apply power to it.  I usually start with having a good look at all the capacitors and resistors, and make a list of needed, obvious, replacements. All of the old 'sangamo' molded plastic caps will be replaced, the same goes for all the electrolytics. One potentiometer is also stuck and will probably need replacing.

Mouser carries the needed capacitors, below is a shopping list:

Capacitor list


.1uf 600v 100nf 418P10496LB3

.25uf 600v 250nf 418P25496MB3

.5uf 350v 500nf, schematic calls for .25uf, change to 0.25

40uf 150v  bias supply. go with 47uf 160v 476TTA160M 

8uf 450v 2pc. go with 10uf MAL204217109E3

.05uf 600v 50nf  6PSS50

20uf 25vdc 40vac TVA1305.5

.005uf 600v 5nf  S502M39Z5UN63L6R

.002uf 600v 2nf  S202M29Z5UN63L6R

40uf 450v 2pc, we go with 47uf axial caps.   MAL204317479E3 


QT1 vox unit :

50uf 30v TE1307-E3

.002uf 600v S202M29Z5UN63L6R

.1uf 600v 418P10496LB3

.05uf 600v 6PSS50


Alterations of capacitor values


A few of the capacitor values will be adjusted to suit modern, stocked, parts. When a capacitor is not in any frequency dependant circuit, I see no problem going to the nearest convenient value. As an example; the BC-455 receiver I recapped got all the bypass caps replaced, and I used 100nf caps instead of the original 50nf. Why? because the 100nf caps were available in 250V versions, meaning a smaller size, than the 50nf ones that I could only find in 600V rating. 


Anyway, the capacitors are ordered and should be on their on the way. Now to start wondering about the cosmetics. 

Stay tuned!


The manual with the original schematic 


Time flies. 70 years old 





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