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Old 11th Sep 2019, 2:57 am   #22
Silicon
Nonode
 
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,152
Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

I believe they are single plate Selenium rectifiers. There may be 7 of these in your receiver.

They are used for AGC, noise limiting and 'grid desensitising' functions.

The forward voltage drop may be about 5V and that would explain why you get no reading on the diode test. The reverse breakdown voltage may be as low as 20V.

If you desolder one end of each diode you could test them with a 9V PP3 battery wired in series with a 10kOhm resistor.

The AGC and noise limiter circuits may have been designed to make use of their characteristics.

If you replace them with a typical signal diode such as a 1N4148, you may alter the performance of the receiver.
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