Mystery valve - UK Vintage Radio Repair and Restoration Discussion Forum

radiograham · 15th Jun 2018, 12:30 am

I have had these valves for about 10 years but have never identified them. They are a large B9A based triode/pentode looking very much like a PCL85 but I have tested them as such and they aren't. The strange thing is they have heaters on the usual pins 4 and 5, plus a tap on pin 1. I have never seen this before. Also I dont think this is a centre tap for series/parallel operation as the resistance is different between the two sections, Any ideas anyone?

Silicon · 15th Jun 2018, 9:29 am

I looked through the B9a valve base diagrams in the Radio Valve and Transistor Data book 9th edition) but could not see anything with the same heater connections as your valve.
The book mainly deals with British and the popular American valves.

Your valves may be American. I have a vague memory of an output or rectifier valve with a tapping on the heater.

vidjoman · 15th Jun 2018, 9:33 am

Maybe pin 1 is used as a support to join the two filament sections and is marked as NC .

ms660 · 15th Jun 2018, 9:34 am

Pics.

Lawrence.

GrimJosef · 15th Jun 2018, 9:45 am

If you had just one valve like this then I'd fear that pin 1 is actually a cathode connection and a heater-cathode short has developed. But if you have several and they're all the same (and not all damaged in the same way !) then that would rule that out. As Lawrence says, pictures would help a lot. Several close-up ones showing the connections between the valve electrodes and the pins would be particularly useful.

Cheers,

GJ

Silicon · 15th Jun 2018, 10:22 am

A triode pentode valve would normally use all of the pins.

If pin 1 was normally connected to chassis i.e screening, G3, etc then it could also be used for one of the heater connections.

David Simpson · 15th Jun 2018, 10:36 am

Is all the ident lettering completely obliterated ? Have you tried the "Hot Breath" method of studying the glass for a feint residual image ? DONT try washing the glass envelope or cleaning with white spirit. Quite a few American valves have lettering/numbering on the bakelite base. Yes please for pictures.

Regards, David

Boater Sam · 15th Jun 2018, 10:56 am

Bakelite base on a B9A?
Could it be Russian? Check the diameter, many Russian valves are 1mm bigger than normal.

barrymagrec · 15th Jun 2018, 1:26 pm

Are you sure that it isn`t a taller double triode? 12BH7?

Are the two halves visually similar?

radiograham · 15th Jun 2018, 5:29 pm

Quote:

Originally Posted by ms660

Pics.

I Intended to send pics, but dont know how to. Can you tell me how you upload pics to the forum.

ms660 · 15th Jun 2018, 5:40 pm

Re: Uploading pics:

https://www.vintage-radio.net/forum/...ad.php?t=77650

Lawrence.

radiograham · 16th Jun 2018, 12:07 am

Hopefuly pics attached. The valves have no legible markings, I have tried to see the inside with magnifying glass and as far as I can see pin 5 is one side of pentode heater, the other side of which goes via a connection to pin 1 which is one side of triode heater, the other side going to pin 4. So it looks like the two heaters are in series pin 1 being a anchor point,

Diabolical Artificer · 16th Jun 2018, 8:36 am

For the life of me can't see a tap. Is that an etch code there? Can't quite read it - B**4* ? Lastly if that pencil "C" is on the anode, not on the glass, I've seen that before, can't remember where though.

A.

Dave Moll · 16th Jun 2018, 9:05 am

Judging by the shadow, the "C" is on the glass.

Station X · 16th Jun 2018, 9:19 am

According to the first post, the tap has been identified by measuring the resistance between pins.

Silicon · 16th Jun 2018, 9:41 am

When I look at picture 2 it seems as if the large anode structure is strapped to the smaller anode structure.
I also get the impression that the large anode is linked to the G3 support rod.

This valve could be a prototype or a special industrial valve.

Biggles · 16th Jun 2018, 9:46 am

Looks like a triode-pentode to me. You could always connect a psu to pins 4 and 5 and wind it up slowly, measuring current and voltage for a reasonable orange glow. This would eliminate a few possibilities if you could get some heater data.
Alan.

GrimJosef · 16th Jun 2018, 9:50 am

Quote:

Originally Posted by Diabolical Artificer

For the life of me can't see a tap ...

I've tried to colour the heater connections as I see them Andy. Pin 4 (green) does indeed seem to be connected to one end of the triode heater and Pin 5 (blue) to one end of the pentode heater. One of my red lines drops down (that's down in the picture, or up in the valve) from Pin 1 and is welded to a piece of small flat bar which has been bent into a square U shape. My other red line follows the top (in the picture) edge of that bar. You can clearly see that it's fastened to the other end of the pentode heater and, less clearly, that it goes to the triode heater too. So radiograham's conclusion seems correct.

For what it's worth other pictures seem to show that the triode grid goes to Pin 2 and the triode cathode to Pin 3.

And that definitely does look like a Philips/Mullard Blackburn code.

Cheers,

GJ

G8HQP Dave · 16th Jun 2018, 12:39 pm

In some cases the triode in a triode-pentode will be a copy of that used in other valves, so the anode shape may give a clue. For example, the triode in most Mazda T-Ps is identical to half a 6/30L2 (=ECC804) and has exactly the same anode metal.

However, that does look rather like a Blackburn code - except that it looks a bit smudged, which real codes would not usually be.

AC/HL · 16th Jun 2018, 12:49 pm

They're often referred to as etch codes, but they're paint, so can be damaged.

15th Jun 2018, 12:30 am	#1
radiograham Hexode Join Date: Oct 2017 Location: Manchester, UK. Posts: 363	Mystery valve I have had these valves for about 10 years but have never identified them. They are a large B9A based triode/pentode looking very much like a PCL85 but I have tested them as such and they aren't. The strange thing is they have heaters on the usual pins 4 and 5, plus a tap on pin 1. I have never seen this before. Also I dont think this is a centre tap for series/parallel operation as the resistance is different between the two sections, Any ideas anyone?

15th Jun 2018, 9:29 am	#2
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,167	Re: Mystery valve I looked through the B9a valve base diagrams in the Radio Valve and Transistor Data book 9th edition) but could not see anything with the same heater connections as your valve. The book mainly deals with British and the popular American valves. Your valves may be American. I have a vague memory of an output or rectifier valve with a tapping on the heater.

15th Jun 2018, 9:33 am	#3
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: Mystery valve Maybe pin 1 is used as a support to join the two filament sections and is marked as NC .

15th Jun 2018, 9:34 am	#4
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Mystery valve Pics. Lawrence.

15th Jun 2018, 9:45 am	#5
GrimJosef Dekatron Join Date: Sep 2007 Location: Oxfordshire, UK. Posts: 4,311	Re: Mystery valve If you had just one valve like this then I'd fear that pin 1 is actually a cathode connection and a heater-cathode short has developed. But if you have several and they're all the same (and not all damaged in the same way !) then that would rule that out. As Lawrence says, pictures would help a lot. Several close-up ones showing the connections between the valve electrodes and the pins would be particularly useful. Cheers, GJ __________________ http://www.ampregen.com

15th Jun 2018, 10:22 am	#6
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,167	Re: Mystery valve A triode pentode valve would normally use all of the pins. If pin 1 was normally connected to chassis i.e screening, G3, etc then it could also be used for one of the heater connections.

15th Jun 2018, 10:36 am	#7
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,857	Re: Mystery valve Is all the ident lettering completely obliterated ? Have you tried the "Hot Breath" method of studying the glass for a feint residual image ? DONT try washing the glass envelope or cleaning with white spirit. Quite a few American valves have lettering/numbering on the bakelite base. Yes please for pictures. Regards, David

15th Jun 2018, 10:56 am	#8
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Mystery valve Bakelite base on a B9A? Could it be Russian? Check the diameter, many Russian valves are 1mm bigger than normal.

15th Jun 2018, 1:26 pm	#9
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,560	Re: Mystery valve Are you sure that it isn`t a taller double triode? 12BH7? Are the two halves visually similar?

15th Jun 2018, 5:40 pm	#11
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Mystery valve Re: Uploading pics: https://www.vintage-radio.net/forum/...ad.php?t=77650 Lawrence.

16th Jun 2018, 12:07 am	#12
radiograham Hexode Join Date: Oct 2017 Location: Manchester, UK. Posts: 363	Re: Mystery valve Hopefuly pics attached. The valves have no legible markings, I have tried to see the inside with magnifying glass and as far as I can see pin 5 is one side of pentode heater, the other side of which goes via a connection to pin 1 which is one side of triode heater, the other side going to pin 4. So it looks like the two heaters are in series pin 1 being a anchor point, Attached Thumbnails

16th Jun 2018, 8:36 am	#13
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,667	Re: Mystery valve For the life of me can't see a tap. Is that an etch code there? Can't quite read it - B*4 ? Lastly if that pencil "C" is on the anode, not on the glass, I've seen that before, can't remember where though. A. __________________ Curiosity hasn't killed this cat...so far.

16th Jun 2018, 9:05 am	#14
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,130	Re: Mystery valve Judging by the shadow, the "C" is on the glass. __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

16th Jun 2018, 9:19 am	#15
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Mystery valve According to the first post, the tap has been identified by measuring the resistance between pins. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

16th Jun 2018, 9:41 am	#16
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,167	Re: Mystery valve When I look at picture 2 it seems as if the large anode structure is strapped to the smaller anode structure. I also get the impression that the large anode is linked to the G3 support rod. This valve could be a prototype or a special industrial valve.

16th Jun 2018, 9:46 am	#17
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Re: Mystery valve Looks like a triode-pentode to me. You could always connect a psu to pins 4 and 5 and wind it up slowly, measuring current and voltage for a reasonable orange glow. This would eliminate a few possibilities if you could get some heater data. Alan.

16th Jun 2018, 12:39 pm	#19
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Mystery valve In some cases the triode in a triode-pentode will be a copy of that used in other valves, so the anode shape may give a clue. For example, the triode in most Mazda T-Ps is identical to half a 6/30L2 (=ECC804) and has exactly the same anode metal. However, that does look rather like a Blackburn code - except that it looks a bit smudged, which real codes would not usually be.

16th Jun 2018, 12:49 pm	#20
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Mystery valve They're often referred to as etch codes, but they're paint, so can be damaged.