A "found" triode... - UK Vintage Radio Repair and Restoration Discussion Forum

G6Tanuki · 22nd Oct 2019, 8:04 pm

Discovered recently: all signs of identification are missing except for the number "67" on the top mica-support.

It's indirectly heated and the filament appears quite thin so I'm thinking 6.3V? The anode is a 'box' style one made from two pressings riveted together - about 1.5 inches high and an inch wide.

5-pin "British" type base - whose only significant feature is that there's a small 'step' on the part of the bakelite right next to where it's bonded to the glass - does that suggest any particular manufacturer?

I haven't experimented with applying heater voltage/current yet - that happens tomorrow.

Any ideas what it might be? Assuming it has heater-connectivity, I'm tempted to see if it works as a "Pierce" crystal-oscillator around 2MHz.

G3VKM_Roger · 22nd Oct 2019, 8:23 pm

ML4 or ML6 maybe?

73

Roger

G6Tanuki · 23rd Oct 2019, 10:12 am

I've done some testing of the heater, hooking it to my variable-voltage PSU and slowly winding the volts up to see what happened.

See screenshot below. At 4V the bits of the heaters sticking out the end of the cathode were nicely orange, though the cathode itself was only glowing a very dull orange.

Now, if only I can find my stash of British 5-pin valve sockets!

FERNSEH · 23rd Oct 2019, 10:31 am

The Marconi-Osram ML6 was possibly the only 6.3volt valve on a B5 base.
Can't think of any others.

https://www.radiomuseum.org/tubes/tube_ml6.html

DFWB

G6Tanuki · 23rd Oct 2019, 10:59 am

Looking at the heater current I think that mine's a ML4.

G3VKM_Roger · 24th Oct 2019, 6:24 am

If you can't find a B5 base then P/M me as I should have several ex-RAF in stock.

73

Roger

cmjones01 · 24th Oct 2019, 8:25 am

That should work well as an RF oscillator. The Marconi TF144G signal generator uses them.

Chris

kalee20 · 24th Oct 2019, 8:42 am

From memory, the MH4 triode was 4V, 1A.

I didn't know there were ANY 6.3V heaters on B4 or B5 bases till Fernshe's post above!

The difference between MH4 and ML4 is anode resistance and mutual conductance, a bit like the difference between ECC82 and ECC83.

Heatercathodeshort · 24th Oct 2019, 5:46 pm

When I was a kid I remember building a one valve radio with an ML4. The HT was a B126 90v battery with a bell transformer set on the 4v tapping for the heater. I wound a large frame aerial and the performance was incredible at Wimbledon.

A very versatile valve the ML4 and I'm almost certain it was used as scanning drivers in the pre war GEC electrostatic television receivers. J.

G6Tanuki · 27th Oct 2019, 6:23 pm

Update: using the brass connector-barrels from 'choc-blocks' for valve-pin-connections rather than a proper valve-base, an old "10XJ" crystal on 3481.5KHz (made by Brush), a 10KOhm grid-leak and an ex-military radio-frequency choke marked "10A/10117", this antique triode oscillates nicely - settling down to draw 24mA at 300V HT, producing enough RF to light a 6-volt 60mA bulb to reasonable brightness.

I'm now thinking about building it into a "Retro" crystal-calibrator/marker-oscillator of some sort, in an Eddystone diecast box - I've got some obscure-frequency 10X- and FT243 crystals that could be used, and I'm thinking of sticking a 2-Ohm 2-Watt resistor in series with the heater so I can power it from my generic 6.3/250V shack-supplies [probably via a Jones-plug].

22nd Oct 2019, 8:04 pm	#1
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	A "found" triode... Discovered recently: all signs of identification are missing except for the number "67" on the top mica-support. It's indirectly heated and the filament appears quite thin so I'm thinking 6.3V? The anode is a 'box' style one made from two pressings riveted together - about 1.5 inches high and an inch wide. 5-pin "British" type base - whose only significant feature is that there's a small 'step' on the part of the bakelite right next to where it's bonded to the glass - does that suggest any particular manufacturer? I haven't experimented with applying heater voltage/current yet - that happens tomorrow. Any ideas what it might be? Assuming it has heater-connectivity, I'm tempted to see if it works as a "Pierce" crystal-oscillator around 2MHz. Attached Thumbnails

22nd Oct 2019, 8:23 pm	#2
G3VKM_Roger Heptode Join Date: Jun 2012 Location: Southeast Norfolk, UK. Posts: 773	Re: A "found" triode... ML4 or ML6 maybe? 73 Roger

23rd Oct 2019, 10:12 am	#3
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: A "found" triode... I've done some testing of the heater, hooking it to my variable-voltage PSU and slowly winding the volts up to see what happened. See screenshot below. At 4V the bits of the heaters sticking out the end of the cathode were nicely orange, though the cathode itself was only glowing a very dull orange. Now, if only I can find my stash of British 5-pin valve sockets! Attached Thumbnails

23rd Oct 2019, 10:31 am	#4
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: A "found" triode... The Marconi-Osram ML6 was possibly the only 6.3volt valve on a B5 base. Can't think of any others. https://www.radiomuseum.org/tubes/tube_ml6.html DFWB

23rd Oct 2019, 10:59 am	#5
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: A "found" triode... Looking at the heater current I think that mine's a ML4.

24th Oct 2019, 6:24 am	#6
G3VKM_Roger Heptode Join Date: Jun 2012 Location: Southeast Norfolk, UK. Posts: 773	Re: A "found" triode... If you can't find a B5 base then P/M me as I should have several ex-RAF in stock. 73 Roger

24th Oct 2019, 8:25 am	#7
cmjones01 Nonode Join Date: Oct 2008 Location: Warsaw, Poland and Cambridge, UK Posts: 2,679	Re: A "found" triode... That should work well as an RF oscillator. The Marconi TF144G signal generator uses them. Chris __________________ What's going on in the workshop? http://martin-jones.com/

24th Oct 2019, 8:42 am	#8
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,087	Re: A "found" triode... From memory, the MH4 triode was 4V, 1A. I didn't know there were ANY 6.3V heaters on B4 or B5 bases till Fernshe's post above! The difference between MH4 and ML4 is anode resistance and mutual conductance, a bit like the difference between ECC82 and ECC83.

24th Oct 2019, 5:46 pm	#9
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: A "found" triode... When I was a kid I remember building a one valve radio with an ML4. The HT was a B126 90v battery with a bell transformer set on the 4v tapping for the heater. I wound a large frame aerial and the performance was incredible at Wimbledon. A very versatile valve the ML4 and I'm almost certain it was used as scanning drivers in the pre war GEC electrostatic television receivers. J.

27th Oct 2019, 6:23 pm	#10
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: A "found" triode... Update: using the brass connector-barrels from 'choc-blocks' for valve-pin-connections rather than a proper valve-base, an old "10XJ" crystal on 3481.5KHz (made by Brush), a 10KOhm grid-leak and an ex-military radio-frequency choke marked "10A/10117", this antique triode oscillates nicely - settling down to draw 24mA at 300V HT, producing enough RF to light a 6-volt 60mA bulb to reasonable brightness. I'm now thinking about building it into a "Retro" crystal-calibrator/marker-oscillator of some sort, in an Eddystone diecast box - I've got some obscure-frequency 10X- and FT243 crystals that could be used, and I'm thinking of sticking a 2-Ohm 2-Watt resistor in series with the heater so I can power it from my generic 6.3/250V shack-supplies [probably via a Jones-plug].