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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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15th Jun 2018, 12:30 am | #1 |
Hexode
Join Date: Oct 2017
Location: Manchester, UK.
Posts: 363
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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?
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15th Jun 2018, 9:29 am | #2 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,167
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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 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,326
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Re: Mystery valve
Maybe pin 1 is used as a support to join the two filament sections and is marked as NC .
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15th Jun 2018, 9:34 am | #4 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Mystery valve
Pics.
Lawrence. |
15th Jun 2018, 9:45 am | #5 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
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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
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15th Jun 2018, 10:22 am | #6 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,167
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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 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,857
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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 |
Banned
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
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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 |
Octode
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,560
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Re: Mystery valve
Are you sure that it isn`t a taller double triode? 12BH7?
Are the two halves visually similar? |
15th Jun 2018, 5:29 pm | #10 |
Hexode
Join Date: Oct 2017
Location: Manchester, UK.
Posts: 363
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Re: Mystery valve
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15th Jun 2018, 5:40 pm | #11 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Mystery valve
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16th Jun 2018, 12:07 am | #12 |
Hexode
Join Date: Oct 2017
Location: Manchester, UK.
Posts: 363
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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,
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16th Jun 2018, 8:36 am | #13 |
Dekatron
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,667
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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.
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16th Jun 2018, 9:05 am | #14 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,130
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Re: Mystery valve
Judging by the shadow, the "C" is on the glass.
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16th Jun 2018, 9:19 am | #15 |
Moderator
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Location: Ipswich, Suffolk, IP4, UK.
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Re: Mystery valve
According to the first post, the tap has been identified by measuring the resistance between pins.
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
16th Jun 2018, 9:41 am | #16 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,167
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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 |
Rest in Peace
Join Date: Feb 2004
Location: Hexham, Northumberland, UK.
Posts: 2,234
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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, 9:50 am | #18 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
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Re: Mystery valve
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
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16th Jun 2018, 12:39 pm | #19 |
Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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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 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,642
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Re: Mystery valve
They're often referred to as etch codes, but they're paint, so can be damaged.
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