DM70 valve? - UK Vintage Radio Repair and Restoration Discussion Forum

dominicbeesley · 1st Sep 2008, 1:46 pm

I just found this valve in a bag of general junk valves. I tried the fridge/breathe method of revealing the number but that just resulted in the last of the black lettering falling away!

I've no idea what it really is, the closest looking I could find on the National Valve Museum was DM70.

Are these particularly rare/special/expensive? I'm considering putting it in a project but wouldn't want to break something "special" (If they're cheap I'd like a few to make up a display

)

Dom

Robert Darwent · 1st Sep 2008, 3:21 pm

Hi Dom,

It certainly looks like a DM70, or more likely a DM71 which is basically a DM70 with short leads. I have a few sets which use DM70's and DM71's as tuning indicators and they too have the same 'exclamation mark' type display like your valve. If it does prove to be a DM70/71 then they are not particularly rare or expensive. I recently purchased a couple of NOS DM70's from the USA for around £9 the pair including delivery.

Regards

dominicbeesley · 1st Sep 2008, 4:27 pm

Thanks for the quick reply. I'll not feel too guilty about making something pretty from it then!

Dom

Sideband · 1st Sep 2008, 4:36 pm

Yes...odd little things really. There are some Ekco sets that use them I think and the Every Ready Sky Emporer. I also had an old Philips tape recorder (EL3527) that used it.

Rich.

Mike Phelan · 1st Sep 2008, 5:08 pm

Some of the Far Eastern mains valve radios like Unitra used them as well. The display was not very easy to show whan you were "tuned in".

jim_beacon · 1st Sep 2008, 5:49 pm

They were also used as transmitter tuning indicators on some military "portable" transmitters.

Jim.

kalee20 · 1st Sep 2008, 6:30 pm

I've seen one used as a balance indicator on a small battery-operated Nombrex CR bridge. And I think that they were used as tuning indicators on at least one Eddystone communications receiver.

Nickthedentist · 1st Sep 2008, 6:34 pm

If it eventually turns out to be surplus to requirements, I have a slightly tatty Ekco U243 which has a DM70 with virtually no emission. But I suppose yours may be no better, as they did have a bit of a reputation for early failure.

Nick.

dominicbeesley · 2nd Sep 2008, 4:12 pm

Poked it into the AVO last night and it lights up surprisingly well with an 85V anode voltage. The pattern is a very thin exclamation mark, not bulbous like the cutout would suggest.

Nick if you want it I'll swap it for a bog-standard tuning indicator. I'd like one for a rough and ready S-meter on my homebrew amateur receiver, if you're not bothered though this little valve would do perfectly!

Dom

paulsherwin · 2nd Sep 2008, 4:18 pm

DM70s were designed as battery valves, but were used quite widely as tuning indicators in small mains FM sets. Their heater voltage is derived from the O/P valve cathode, and when That Capacitor starts to leak, the voltage goes through the roof and wrecks the valve.

Paul

1st Sep 2008, 1:46 pm	#1
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	DM70 valve? I just found this valve in a bag of general junk valves. I tried the fridge/breathe method of revealing the number but that just resulted in the last of the black lettering falling away! I've no idea what it really is, the closest looking I could find on the National Valve Museum was DM70. Are these particularly rare/special/expensive? I'm considering putting it in a project but wouldn't want to break something "special" (If they're cheap I'd like a few to make up a display) Dom Attached Thumbnails

1st Sep 2008, 3:21 pm	#2
Robert Darwent Heptode Join Date: Aug 2006 Location: Sheffield, South Yorkshire, UK Posts: 990	Re: DM70 valve? Hi Dom, It certainly looks like a DM70, or more likely a DM71 which is basically a DM70 with short leads. I have a few sets which use DM70's and DM71's as tuning indicators and they too have the same 'exclamation mark' type display like your valve. If it does prove to be a DM70/71 then they are not particularly rare or expensive. I recently purchased a couple of NOS DM70's from the USA for around £9 the pair including delivery. Regards __________________ Robert G0UHF www.wavesintheair.co.uk

1st Sep 2008, 4:27 pm	#3
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: DM70 valve? Thanks for the quick reply. I'll not feel too guilty about making something pretty from it then! Dom

1st Sep 2008, 4:36 pm	#4
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,577	Re: DM70 valve? Yes...odd little things really. There are some Ekco sets that use them I think and the Every Ready Sky Emporer. I also had an old Philips tape recorder (EL3527) that used it. Rich. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

1st Sep 2008, 5:08 pm	#5
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: DM70 valve? Some of the Far Eastern mains valve radios like Unitra used them as well. The display was not very easy to show whan you were "tuned in". __________________ Mike.

1st Sep 2008, 5:49 pm	#6
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Re: DM70 valve? They were also used as transmitter tuning indicators on some military "portable" transmitters. Jim.

1st Sep 2008, 6:30 pm	#7
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,087	Re: DM70 valve? I've seen one used as a balance indicator on a small battery-operated Nombrex CR bridge. And I think that they were used as tuning indicators on at least one Eddystone communications receiver.

1st Sep 2008, 6:34 pm	#8
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,855	Re: DM70 valve? If it eventually turns out to be surplus to requirements, I have a slightly tatty Ekco U243 which has a DM70 with virtually no emission. But I suppose yours may be no better, as they did have a bit of a reputation for early failure. Nick.

2nd Sep 2008, 4:12 pm	#9
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: DM70 valve? Poked it into the AVO last night and it lights up surprisingly well with an 85V anode voltage. The pattern is a very thin exclamation mark, not bulbous like the cutout would suggest. Nick if you want it I'll swap it for a bog-standard tuning indicator. I'd like one for a rough and ready S-meter on my homebrew amateur receiver, if you're not bothered though this little valve would do perfectly! Dom

2nd Sep 2008, 4:18 pm	#10
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,958	Re: DM70 valve? DM70s were designed as battery valves, but were used quite widely as tuning indicators in small mains FM sets. Their heater voltage is derived from the O/P valve cathode, and when That Capacitor starts to leak, the voltage goes through the roof and wrecks the valve. Paul