Cossor MVS-PEN-B fault

[gary_crutchley]

Hi all,

I have a Cossor MVS-PEN-B valve which has a fault. When I replace the working valve in my Bush SW43 with this particular valve, I get audio but also a pronounced rhythmic "beat".

Does anyone know what's wrong, is it an internal short?

Is there anything that can be done to rescue the valve?

Best regards,

Gary

[Cobaltblue]

Hi Gary

This ISTR is a metalised valve.

Its possible the the metalisation ( grey coating) has lost its connection with the wire that grounds it.

The wire should be visable at the base of the valve wrapped around.

if it has the connection can be re-made using a conductive paint.

Cheers

Mike T

[gary_crutchley]

Hi Mike,

Thanks for the advice. Can you clarify where I am looking please? The Bakelite base on this valve is intact, should I be able to see the wire with it in place?

Regards,

Gary

[Cobaltblue]

Hi Gary the wire is usually in the join between the glass bulb and the base.

Unless the coating has flaked or the base is loose this connection is usually pretty good on Cossor valves.

to check to see if it is a coating issue you can temporarily wrap the valve in tinfoil avoiding the pins and top cap, wrap a piece of wire around it near the join and connect it straight to chassis.

The the fault remains then the coating is not the cause.

Cheers

Mike T

[gary_crutchley]

Hi Mike,

I just wanted to let you know that I tried the test that you suggested above. The valve was making the same beating noise before I connected the temporary wire to the chassis, then once connected it stopped.

But not only that, once I removed the tinfoil and the temporary wire it continued to work. Hence it was the connection problem that you suggested. I think compressing the wire and the coating together temporarily remade the connection between the two. Hence I am pretty confident some conductive paint will solve the problem. Do you have any suggestions on the type of paint to use please?

Also what does the wire connected to the coating actually do, does it simply earth the coating?

Many thanks,

Gary

[Cobaltblue]

Hi Gary yes it earths the coating.

Heater windscreen repair paint can help its a silver loaded paint.

This is a pretty common problem.

Cheers Mike T

[gary_crutchley]

Thanks Mike.