1950s rectifiers. - UK Vintage Radio Repair and Restoration Discussion Forum

G6Tanuki · 9th Sep 2016, 9:32 pm

I'm playing with a prototype aircraft radio power-supply from the 1950s - it has a pair of old-style rectifiers in the bias-supply for the transmitter.

These are marked "FSW 7199A" and "10D 19247 C56"

Thsy're clearly old-style copper-oxide-disc or selenium-stack beasties - any ideas what sorts of forward- and reverse-resistances I should be expecting to find if they're healthy/

From what I can work out they're expected to provide a -ve bias rail of around 75V.

Marconi_MPT4 · 10th Sep 2016, 9:52 pm

Quote:

Originally Posted by G6Tanuki

..These are marked "FSW 7199A" and "10D 19247 C56"

Just rummaged through all data books pertaining to selenium rectifiers and reasonably sure FSW xxx was manufactured by STC/Brimar. Unfortunately no data as yet but may be possible to estimate resistance based on the number of cells used.

Rich

orbanp1 · 11th Sep 2016, 12:08 am

Hi Tanuki,

The data I see from an old (early '60s) handbook, indicates that the forward resistance depends on the load current. The higher the current, the lower the resistance.
There was no data on the reverse leakage current.
A single element handles about 25V.

So you basically have to check it under the load.

I can copy a table listing the min resistances and max currents of various diameter selenium disk elements, if you are interested in.

Regards, Peter

orbanp1 · 11th Sep 2016, 1:35 pm

Did find some characteristic curves in a later edition of the handbook.
They show the forward and reverse bias curves, for different grade selenium plates.

Hope it helps, Peter

FrankB · 12th Sep 2016, 6:35 am

The best way to check them is with a load. IIRC, there was an article I saw on building a test jig for them, Possibly in Electronic Servicing & Technology magazine. That publisher is defunct, but you may be able to find a copy of the article online. (Gee- that was maybe 30+ yrs. back I saw the article.)

Hartley118 · 12th Sep 2016, 9:21 am

Quote:

Originally Posted by orbanp1

Did find some characteristic curves in a later edition of the handbook.
They show the forward and reverse bias curves, for different grade selenium plates.

Interesting.............Looking at those curves, not so much a rectifier, more a directional resistor.

Martin

G6Tanuki · 16th Sep 2016, 7:49 pm

Thanks for the guidance: given that they're used in a power supply to provide something like 50V of negative-bias and the maximum current drain is around 10mA I've replaced them with a couple of OA202 diodes I happened to have handy.

http://www.radiomuseum.org/tubes/tube_oa202.html

So far, so good.

9th Sep 2016, 9:32 pm	#1
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	1950s rectifiers. I'm playing with a prototype aircraft radio power-supply from the 1950s - it has a pair of old-style rectifiers in the bias-supply for the transmitter. These are marked "FSW 7199A" and "10D 19247 C56" Thsy're clearly old-style copper-oxide-disc or selenium-stack beasties - any ideas what sorts of forward- and reverse-resistances I should be expecting to find if they're healthy/ From what I can work out they're expected to provide a -ve bias rail of around 75V.

11th Sep 2016, 12:08 am	#3
orbanp1 Heptode Join Date: Nov 2009 Location: London, Ontario, Canada Posts: 675	Re: 1950s rectifiers. Hi Tanuki, The data I see from an old (early '60s) handbook, indicates that the forward resistance depends on the load current. The higher the current, the lower the resistance. There was no data on the reverse leakage current. A single element handles about 25V. So you basically have to check it under the load. I can copy a table listing the min resistances and max currents of various diameter selenium disk elements, if you are interested in. Regards, Peter

12th Sep 2016, 6:35 am	#5
FrankB Heptode Join Date: Oct 2005 Location: Olympia, Washington, USA. Posts: 664	Re: 1950s rectifiers. The best way to check them is with a load. IIRC, there was an article I saw on building a test jig for them, Possibly in Electronic Servicing & Technology magazine. That publisher is defunct, but you may be able to find a copy of the article online. (Gee- that was maybe 30+ yrs. back I saw the article.)

16th Sep 2016, 7:49 pm	#7
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: 1950s rectifiers. Thanks for the guidance: given that they're used in a power supply to provide something like 50V of negative-bias and the maximum current drain is around 10mA I've replaced them with a couple of OA202 diodes I happened to have handy. http://www.radiomuseum.org/tubes/tube_oa202.html So far, so good.