Marconi DEV Type valves

[David Simpson]

Folks, I've been asked to test 6 Marconi DEV type clip held valves. Am I correct in assuming that, say, a D.E.V.368 has a 3V Filament & a Va of 68V ? There is also a D.E.Q.209D. Some have missing or unreadable numbering.
I've been told that they are as rare as rocking horse manure, so need to be jolly sure that I'm applying the correct voltages. I ken that the end caps are the filament & the green side cap is the anode. Any info &/or advice most welcome, please.
I've downloaded some basic info off the internet, but any detailed valve testing info would be most appreciated.

Regards, David

[ms660]

I don't know if you've come across this, it's from WW, 30th April 1924...magazine page 138 (scroll down it's near the bottom)

"Valve Tests. The Marconi-Osram DEV and DEQ"....some curves etc are shown:

http://www.americanradiohistory.com/...4-04-S-OCR.pdf

Lawrence.

[M0FYA Andy]

Rocking horse manure? It looks like you've got the whole muck-heap there!
Lucky chap.

Andy

[ColinTheAmpMan1]

Hi David,
You might consider getting hold of a copy of "The Saga of Marconi Osram Valve" by Barry Vyse and George Jessop (you can buy it from Barry Vyse at Vyse Ltd.) There is some historical information on these valves, but I can't see any detail that might answer your questions, other than that they seem to be dull emitters. Lawrence's reference gives some more useful info.

Andy, David isn't as lucky as you might think, as he has said he's been asked to test these valves, not that they're his property.
Colin.

[David Simpson]

I've managed to get some decent gen(mu, ra, & gm) off museum sites, and Lawrence's site has given me great gen on testing - including graphs.
So far, by heavy breathing & a magnifying lamp, I've managed to read off the following faded numbering :-
(a) D.E.V.398, (b) D.E.V.365, (c) D.E.Q.200D, (d) D.E.V. E??, (e) & (f) = D.E.V. 's.
The AWA Radio Guide "Marconi" info says Filament = 3V at 0.2A, and max Va = 60V for the DEV's & DEQ's. And the "Victoria Collections" site confirms the same filament supply. Lawrence's 1924 site info says filament is 2.75V/0.2A, & their working graph Va voltages are 20 & 40V.

Regards, David

[PJL]

Seems a little crazy testing these. If the filaments are intact then I would call that a good one!

These are bright emitters and were used with rheostats to adjust the voltage until you get the correct brightness and/or anode current flow. You can't just apply the recommended filament voltage as with dull emitter valves. However, I would guess that any air that has entered in the past 100 years is likely to cause the filament to fail pretty quickly.

I suppose you could have a go with one and wind the filament voltage up gently and see if it shows any signs of behaving like a valve.

[David Simpson]

Right enough PJL, these valves are nigh on 100 years old. They belong to a local chum & very keen 1920's radio restorer, and BVWS member. If they work they'll actually be fitted into one of his current projects. I've already tested five B4 bulbous triodes of a similar age for him, & they passed with flying colours.
For special valve testing purposes, I have a modern 3 channel digital DC PSU, which can control current down to 10's of mA's. Obviously, with these rare DEV's I'll apply a filament supply very gradually.
First though, I'm going to build a bespoke valve holder rig for these horizontally mounted clipped wee valves.

Regards, David

[Mr Moose]

Hello,
The original valves of this type were the Type V24 and the Type Q. These were both true bright emitters with 5V filaments. (5V filaments would run off a 6V accumulator with a filament rheostat so could be overrun if you needed it.) They came out circa 1916.
http://www.radiomuseum.org/tubes/tube_v24.html
http://www.radiomuseum.org/tubes/tube_q_marconi.html
The DEV and DEQ valves were, as the initial letter might suggest, the dull emitter versions of the V24 and the Q. These had thoriated tungsten filaments so they would run at a bright orange rather than the almost white of a true bright emitter. (They are not oxide coated filaments so they are still bright by modern standards) These had 3V filaments and came out circa 1923.
http://www.radiomuseum.org/tubes/tube_dev.html
http://www.radiomuseum.org/tubes/tube_deq.html
Yours, Richard

[David Simpson]

At last, have managed to get round to building a valve holder for these delicate ancient valves. I'll get the component parts wired together this weekend, then very carefully start testing valves.

Regards, David

[David Simpson]

Plan B initiated :- Replaced side clips for Anode & Grid with Brass spring loaded contacts. Possibility of clips damaging side caps.
This is going to be a slow careful series of tests on all 6 valves.
Have firstly chosen DEV valve no 6 which has missing lettering. For recommended Vf it gives spot-on 0.2A at 3V. More tests to follow.

Regards, David

[David Simpson]

have finally done a Gm Graph for my DEV Valve No6, & compared it with an article titled "Valve Tests" on page 138 of the "Wireless World" dated April 30, 1924. Their valve was just called a "DEV". The 6 I have to test for a BVWS chum have a mixture of worn/missing lettering or numbering.
Using my DC lash-up involves a lot of fannying about. Next - find an old B4 from a duff valvebase & wire it with flyleads so that my wee DEV rig can be connected to my AVO Mk3.

Regards, David

PS. Has anyone out there used or tested DEV valves ?