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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 10th Sep 2019, 11:00 pm   #21
deliverance
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Hi all. There are two rectifiers shown on the bottom right of the picture how do you test them ? I have done a diode test with a multimeter they don't read anything .
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Last edited by deliverance; 10th Sep 2019 at 11:02 pm. Reason: Info
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Old 11th Sep 2019, 2:57 am   #22
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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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Old 11th Sep 2019, 11:44 am   #23
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Thanks for the info I had already ordered the 1N4148 diodes. I can't find any info on the rectifiers in the receiver would the cathode side be the one marked red on the rectifier or is that the anode ?
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Old 11th Sep 2019, 11:57 am   #24
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

RED should be Cathode.
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Old 11th Sep 2019, 12:25 pm   #25
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Thanks Hamish Boxer the receiver is working but the AGC is a bit hit and miss .
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Old 11th Sep 2019, 4:37 pm   #26
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Default Re: Marconi NS702 / 2207E, SN 623 (Atlanta type) receiver

Just for general info on the diodes:

https://www.vintage-radio.net/forum/...4&d=1271872981

Lawrence.
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Old 11th Sep 2019, 6:09 pm   #27
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Default Re: Marconi NS702 / 2207E, SN 623 (Atlanta type) receiver

Some info thanks Lawrence so the anode side is the disc side (red) .
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Old 11th Sep 2019, 7:12 pm   #28
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Default Re: Marconi NS702 / 2207E, SN 623 (Atlanta type) receiver

Quote:
Originally Posted by deliverance View Post
Some info thanks Lawrence so the anode side is the disc side (red) .
Anode is the metal case.

Lawrence.
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Old 11th Sep 2019, 7:36 pm   #29
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Default Re: Marconi NS702 / 2207E, SN 623 (Atlanta type) receiver

Cheers .
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