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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 12th Jan 2021, 8:48 pm   #1
high_vacuum_house's Avatar
Join Date: May 2003
Location: Belper Derbyshire
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Smile 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
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Old 12th Jan 2021, 9:38 pm   #2
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Default Re: Cossor SD6 valve, a strange diode

Info here:

As you say, a bit of an oddball.
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Old 13th Jan 2021, 12:36 am   #3
Join Date: Nov 2011
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Default 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?
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Old 13th Jan 2021, 8:49 am   #4
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Default 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.


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