Filament "spring" in D series battery valves. - UK Vintage Radio Repair and Restoration Discussion Forum

Biggles · 5th Mar 2016, 9:57 pm

I have just been reading one of the excellent Radio Constructor articles by "Dick and Smithy" on the americanradiohistory.com website and they mention that you can visually check for a broken filament in, say, a DK96 valve by simply looking at the position of the filament tensioning spring at the top. It should be level if the filament is ok, and takes on an upward angle if the filament is broken and tension is lost. I haven't actually proved this as I don't have one to hand right now, but I would have thought that the gettering deposits would make this difficult to see. I will dig out my stock tomorrow to check. Any thoughts on this?
Alan.

high_vacuum_house · 5th Mar 2016, 10:08 pm

I have seen this as well.
The spring at the top should be approximately parallel with the top mica but will spring up if the filament snaps (I know this after I wound the filament voltage up on a battery valve radio trying to get it to work when I was a kid causing most of the valves to go with a ping!!) This should also be the case with battery octal valves if the top of the valve is clear.

Christopher Capener

kalee20 · 5th Mar 2016, 11:56 pm

I can usually see the spring.

It's to keep the filament in tension, straight, so it is the correct dustance from the grid wires. Obviously, length changes from cold to hot, due to thermal expansion, so some means for allowing for this has to be provided. Hence the spring!

Peter.N. · 6th Mar 2016, 12:38 am

You often find the spring or bits of it floating about inside the valve, so if its not there the filament has gone.

Peter

5th Mar 2016, 9:57 pm	#1
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Filament "spring" in D series battery valves. I have just been reading one of the excellent Radio Constructor articles by "Dick and Smithy" on the americanradiohistory.com website and they mention that you can visually check for a broken filament in, say, a DK96 valve by simply looking at the position of the filament tensioning spring at the top. It should be level if the filament is ok, and takes on an upward angle if the filament is broken and tension is lost. I haven't actually proved this as I don't have one to hand right now, but I would have thought that the gettering deposits would make this difficult to see. I will dig out my stock tomorrow to check. Any thoughts on this? Alan.

5th Mar 2016, 10:08 pm	#2
high_vacuum_house Octode Join Date: May 2003 Location: Belper Derbyshire Posts: 1,936	Re: Filament "spring" in D series battery valves. I have seen this as well. The spring at the top should be approximately parallel with the top mica but will spring up if the filament snaps (I know this after I wound the filament voltage up on a battery valve radio trying to get it to work when I was a kid causing most of the valves to go with a ping!!) This should also be the case with battery octal valves if the top of the valve is clear. Christopher Capener __________________ Interests in the collection and restoration of Tefifon players and 405 line television

5th Mar 2016, 11:56 pm	#3
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: Filament "spring" in D series battery valves. I can usually see the spring. It's to keep the filament in tension, straight, so it is the correct dustance from the grid wires. Obviously, length changes from cold to hot, due to thermal expansion, so some means for allowing for this has to be provided. Hence the spring!

6th Mar 2016, 12:38 am	#4
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	Re: Filament "spring" in D series battery valves. You often find the spring or bits of it floating about inside the valve, so if its not there the filament has gone. Peter