Cossor SD6 valve, a strange diode - UK Vintage Radio Repair and Restoration Discussion Forum

high_vacuum_house · 12th Jan 2021, 9:48 pm

I found this odd valve in a box of secondhand telly valves and it is a little unusual. It is a single diode in a B7g envelope. There is provision for a second diode and indeed, the second anode is actually installed to support the 2 mica disks with the micas punched to take the cathode tube.

There is no cathode or a heater in this second anode and what looks likely to have been the cathode pin from the base pins (should the second cathode been installed) has been connected to the anode, possibility to add more mechanical support to the cage.

I cannot see the point in developing this valve as a twin diode yet leaving Components out to make it a less useable single diode valve.

Would a single diode in a B7g valve envelope have been worth investing a design in when the EB91 valve would have likely been available with 2 separate diodes in?

Christopher Capener

Sideband · 12th Jan 2021, 10:38 pm

Info here: http://www.r-type.org/exhib/aai0018.htm

As you say, a bit of an oddball.

turretslug · 13th Jan 2021, 1:36 am

The only obvious virtue is the halved (0.15A) heater current- perhaps there was a low-volume requirement for a single diode for something like detector probes and this was a convenient way of using existing jigs that were churning out umpteen double-diodes anyway?

Cobaltblue · 13th Jan 2021, 9:49 am

The SD6 was used in some just post war Cossor TV's such as the 902 which has at least 5 of them.

They are used as video detector, spotter in the video section and has one as the vertical sync separator and another in the horizontal sync separator in the time-base and as an interference limiter in the sound section.
The Sound detector and AFC use the diodes in an OM4

The 902 is a pretty rare beast though.

Cheers

Mike T

12th Jan 2021, 9:48 pm	#1
high_vacuum_house Octode Join Date: May 2003 Location: Belper Derbyshire Posts: 1,935	Cossor SD6 valve, a strange diode I found this odd valve in a box of secondhand telly valves and it is a little unusual. It is a single diode in a B7g envelope. There is provision for a second diode and indeed, the second anode is actually installed to support the 2 mica disks with the micas punched to take the cathode tube. There is no cathode or a heater in this second anode and what looks likely to have been the cathode pin from the base pins (should the second cathode been installed) has been connected to the anode, possibility to add more mechanical support to the cage. I cannot see the point in developing this valve as a twin diode yet leaving Components out to make it a less useable single diode valve. Would a single diode in a B7g valve envelope have been worth investing a design in when the EB91 valve would have likely been available with 2 separate diodes in? Christopher Capener __________________ Interests in the collection and restoration of Tefifon players and 405 line television

12th Jan 2021, 10:38 pm	#2
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,572	Re: Cossor SD6 valve, a strange diode Info here: http://www.r-type.org/exhib/aai0018.htm As you say, a bit of an oddball. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

13th Jan 2021, 1:36 am	#3
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: Cossor SD6 valve, a strange diode The only obvious virtue is the halved (0.15A) heater current- perhaps there was a low-volume requirement for a single diode for something like detector probes and this was a convenient way of using existing jigs that were churning out umpteen double-diodes anyway?

13th Jan 2021, 9:49 am	#4
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,865	Re: Cossor SD6 valve, a strange diode The SD6 was used in some just post war Cossor TV's such as the 902 which has at least 5 of them. They are used as video detector, spotter in the video section and has one as the vertical sync separator and another in the horizontal sync separator in the time-base and as an interference limiter in the sound section. The Sound detector and AFC use the diodes in an OM4 The 902 is a pretty rare beast though. Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk