Yet another unknown valve ... - UK Vintage Radio Repair and Restoration Discussion Forum

Richardgr · 15th Feb 2024, 9:57 pm

I am going through the stash trying to organise them into useful and otherwise.

Anyone have a suggestion for this one?

The base is B8G. There is a paxolin wafer on the pins and a mica sheet against the base. The inside of the glass is some sort of grey coating. The letters are not really disinguishable. X or K, M and then a 4.

turretslug · 15th Feb 2024, 10:03 pm

KT81, or possibly A1820? (Which I suspect is the same valve anyway....). Try measuring the heater current, would be around 0.95A for these.

Richardgr · 15th Feb 2024, 10:16 pm

Thanks! I will try that.

Here is another, Arcturus brand. The text on the base reads (I am 90% sure)
N 5
R 4
Metal base, with one pin missing.

I have found another with the vague bit of a marking on the side, 6 something, 7 GT, 6J7GT I am thinking.

turretslug · 15th Feb 2024, 10:22 pm

Maybe 6J7GT or 6K7GT? Not enough pins or internal connections for 6K8GT. Or maybe the 12V editions thereof.

Richardgr · 24th Mar 2024, 1:19 pm

Thanks for the replies. As luck would have it the thread next to this one was identifying a 6K7GT which looked identical.

Here is another that I cannot find a match for. This one has an ID, but I can't find anything online about what it is used for. Any clues appreciated! I am thinking something linked to Telecoms repeater service?

paulsherwin · 24th Mar 2024, 1:29 pm

Tungsram did use Pnnn codes in the 30s, but I can't help beyond that.

Station X · 24th Mar 2024, 1:57 pm

This eBay listing suggests it's equivalent to a K45, but there's no info on that either:-

https://www.ebay.co.uk/itm/404644868050

Mr Moose · 24th Mar 2024, 2:22 pm

Hello,
Whilst the first valve is most probably a KT81, there is also the KT101.
http://www.r-type.org/exhib/ach0004.htm

The P310 appears to be equivalent to a 310A see data here.
https://frank.pocnet.net/short/054/1/172.pdf

Yours, Richard

Richardgr · 24th Mar 2024, 3:34 pm

Many thanks for that!

This is another odd one. I am fairly certain it is a 309A, but I don't understand the modern box for such an antique looking valve.

I am going through the collection, hoping to get some boxes filled with stuff to get rid off. Vari-mu pentodes are always going to be fearing the reaper's blade, but coming in a box this size does not help their case ...

Richardgr · 24th Mar 2024, 3:39 pm

This one looks like a directly heated triode, on a B4 base?

Mr Moose · 24th Mar 2024, 5:23 pm

Hello,
The B4 triode appears to have the old british military stores number 10E/9856 which is a PX4.
http://www.r-type.org/exhib/aba0002.htm
Yours, Richard

Richardgr · 25th Mar 2024, 1:43 pm

Well, that is better than yet another ECH21!
Thanks!

15th Feb 2024, 9:57 pm	#1
Richardgr Heptode Join Date: Oct 2019 Location: Täby, Sweden Posts: 710	Yet another unknown valve ... I am going through the stash trying to organise them into useful and otherwise. Anyone have a suggestion for this one? The base is B8G. There is a paxolin wafer on the pins and a mica sheet against the base. The inside of the glass is some sort of grey coating. The letters are not really disinguishable. X or K, M and then a 4. Attached Thumbnails

15th Feb 2024, 10:03 pm	#2
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,400	Re: Yet another unknown valve ... KT81, or possibly A1820? (Which I suspect is the same valve anyway....). Try measuring the heater current, would be around 0.95A for these.

15th Feb 2024, 10:16 pm	#3
Richardgr Heptode Join Date: Oct 2019 Location: Täby, Sweden Posts: 710	Re: Yet another unknown valve ... Thanks! I will try that. Here is another, Arcturus brand. The text on the base reads (I am 90% sure) N 5 R 4 Metal base, with one pin missing. I have found another with the vague bit of a marking on the side, 6 something, 7 GT, 6J7GT I am thinking. Attached Thumbnails

15th Feb 2024, 10:22 pm	#4
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,400	Re: Yet another unknown valve ... Maybe 6J7GT or 6K7GT? Not enough pins or internal connections for 6K8GT. Or maybe the 12V editions thereof.

24th Mar 2024, 1:19 pm	#5
Richardgr Heptode Join Date: Oct 2019 Location: Täby, Sweden Posts: 710	Re: Yet another unknown valve ... Thanks for the replies. As luck would have it the thread next to this one was identifying a 6K7GT which looked identical. Here is another that I cannot find a match for. This one has an ID, but I can't find anything online about what it is used for. Any clues appreciated! I am thinking something linked to Telecoms repeater service? Attached Thumbnails

24th Mar 2024, 1:29 pm	#6
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 28,003	Re: Yet another unknown valve ... Tungsram did use Pnnn codes in the 30s, but I can't help beyond that.

24th Mar 2024, 1:57 pm	#7
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Yet another unknown valve ... This eBay listing suggests it's equivalent to a K45, but there's no info on that either:- https://www.ebay.co.uk/itm/404644868050 __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

24th Mar 2024, 2:22 pm	#8
Mr Moose Octode Join Date: Jul 2008 Location: Gloucestershire, UK. Posts: 1,043	Re: Yet another unknown valve ... Hello, Whilst the first valve is most probably a KT81, there is also the KT101. http://www.r-type.org/exhib/ach0004.htm The P310 appears to be equivalent to a 310A see data here. https://frank.pocnet.net/short/054/1/172.pdf Yours, Richard Last edited by Mr Moose; 24th Mar 2024 at 2:27 pm.

24th Mar 2024, 3:34 pm	#9
Richardgr Heptode Join Date: Oct 2019 Location: Täby, Sweden Posts: 710	Re: Yet another unknown valve ... Many thanks for that! This is another odd one. I am fairly certain it is a 309A, but I don't understand the modern box for such an antique looking valve. I am going through the collection, hoping to get some boxes filled with stuff to get rid off. Vari-mu pentodes are always going to be fearing the reaper's blade, but coming in a box this size does not help their case ... Attached Thumbnails

24th Mar 2024, 3:39 pm	#10
Richardgr Heptode Join Date: Oct 2019 Location: Täby, Sweden Posts: 710	Re: Yet another unknown valve ... This one looks like a directly heated triode, on a B4 base? Attached Thumbnails

24th Mar 2024, 5:23 pm	#11
Mr Moose Octode Join Date: Jul 2008 Location: Gloucestershire, UK. Posts: 1,043	Re: Yet another unknown valve ... Hello, The B4 triode appears to have the old british military stores number 10E/9856 which is a PX4. http://www.r-type.org/exhib/aba0002.htm Yours, Richard Last edited by Mr Moose; 24th Mar 2024 at 5:35 pm.

25th Mar 2024, 1:43 pm	#12
Richardgr Heptode Join Date: Oct 2019 Location: Täby, Sweden Posts: 710	Re: Yet another unknown valve ... Well, that is better than yet another ECH21! Thanks!