Valve identity help - UK Vintage Radio Repair and Restoration Discussion Forum

Norman Raeburn · 21st Feb 2020, 4:05 pm

I have this valve in my collection which has no identifiable numbers. Could it be a PX4? Is there any way to positively identify it. I will await answers from the experts. Many thanks, Norman

Ampmatt · 21st Feb 2020, 4:09 pm

Definitely a PX4

barrymagrec · 21st Feb 2020, 4:11 pm

Looks like a PX4 to me - you could check the heater resistance but you would need to know what it should be, cold, which will be quite low.

paulsherwin · 21st Feb 2020, 4:40 pm

It certainly looks like a PX4 - nice condition too.

GrimJosef · 21st Feb 2020, 4:42 pm

Another way to come at it is to ask what it might be if it's not a PX4. I don't think there are very many alternatives are there ?

Cheers,

GJ

PJL · 21st Feb 2020, 6:05 pm

The markings will probably be on the opposite side to the label.

Herald1360 · 21st Feb 2020, 7:04 pm

Stick 4V on the filament pins (start with 2V just in case....)* and see what lights up. Hopefully it will be all of the filament though even if it's only half it could still be used to breathe lower powered life into an old radio.

* Remember the AC042!

greg_simons · 21st Feb 2020, 8:26 pm

Deff px4, you could try shining the light from an led torch on the glass envelope, it can sometimes pick out the faded numbers.
Greg.

Norman Raeburn · 21st Feb 2020, 8:39 pm

I have tried shining a light on it and also tried a uv light source but can’t see anything. I will have another look tomorrow. Norman

Radio Wrangler · 21st Feb 2020, 9:37 pm

I think the only options are to try the filament as Chris says, then find an old enough radio to try it out in.

If you loaned it to an audio aficionado to try out and see if they recognised it by rhythm/pace/authority/granularity and speed of bass, you'd never get it back off them.

It's got to be a triode with that number of pins.... did any half-wave rectifiers look similar?

David

TowerRadio · 21st Feb 2020, 10:14 pm

With the valve fairly cold breath on it ,may reveal a faint ID.Les

snowman_al · 22nd Feb 2020, 8:03 am

Quote:

Originally Posted by GrimJosef

Another way to come at it is to ask what it might be if it's not a PX4. I don't think there are very many alternatives are there ?

Well it could be a PX25 of course...
You will have to measure the filament current to know. A PX4 draws 1 Amp at 4 volts, the PX25 draws 2 Amps. Either way a nice valve to have.

barrymagrec · 22nd Feb 2020, 10:16 am

PX25s are significantly taller....

whiskas · 27th Feb 2020, 7:52 pm

I also think it's a PX4

Norman Raeburn · 27th Feb 2020, 7:57 pm

I am fairly sure it’s a PX4, with 4v heater it draws about 950ma. I have a Taylor valve tester and will give it a go and see how it tests. I will report back with the results. Norman

Norman Raeburn · 11th Mar 2020, 6:17 pm

Hi Folks, To bring this to a conclusion and after repairing my valve tester I have the following results. I don't know how well valve testers compare to book figures.
I have the following result, PX4 mutual conductance reads 4, book states 3.5
I also have a PX25 mutual conductance reads 1.5, book states 4. Is this likely to be duff or is it a case of it may work ok in something. Looking forward to your opinions please. Norman

Herald1360 · 11th Mar 2020, 6:56 pm

Sounds like a good PX4

And a tired PX25

The PX25 will probably still work to some extent in a single ended application and look the part at least.

21st Feb 2020, 4:05 pm	#1
Norman Raeburn Heptode Join Date: Feb 2008 Location: Leven, Fife, Scotland Posts: 823	Valve identity help I have this valve in my collection which has no identifiable numbers. Could it be a PX4? Is there any way to positively identify it. I will await answers from the experts. Many thanks, Norman Attached Thumbnails

21st Feb 2020, 4:09 pm	#2
Ampmatt Diode Join Date: Aug 2019 Location: Sussex, UK. Posts: 5	Re: Valve identity help Definitely a PX4

21st Feb 2020, 4:11 pm	#3
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,557	Re: Valve identity help Looks like a PX4 to me - you could check the heater resistance but you would need to know what it should be, cold, which will be quite low.

21st Feb 2020, 4:40 pm	#4
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,937	Re: Valve identity help It certainly looks like a PX4 - nice condition too.

21st Feb 2020, 4:42 pm	#5
GrimJosef Dekatron Join Date: Sep 2007 Location: Oxfordshire, UK. Posts: 4,311	Re: Valve identity help Another way to come at it is to ask what it might be if it's not a PX4. I don't think there are very many alternatives are there ? Cheers, GJ __________________ http://www.ampregen.com

21st Feb 2020, 6:05 pm	#6
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Valve identity help The markings will probably be on the opposite side to the label.

21st Feb 2020, 7:04 pm	#7
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Valve identity help Stick 4V on the filament pins (start with 2V just in case....)* and see what lights up. Hopefully it will be all of the filament though even if it's only half it could still be used to breathe lower powered life into an old radio. * Remember the AC042! __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

21st Feb 2020, 8:26 pm	#8
greg_simons Octode Join Date: Jul 2004 Location: Evesham, Worcestershire, UK. Posts: 1,422	Re: Valve identity help Deff px4, you could try shining the light from an led torch on the glass envelope, it can sometimes pick out the faded numbers. Greg. __________________ Picture, sound?, DOOR.

21st Feb 2020, 8:39 pm	#9
Norman Raeburn Heptode Join Date: Feb 2008 Location: Leven, Fife, Scotland Posts: 823	Re: Valve identity help I have tried shining a light on it and also tried a uv light source but can’t see anything. I will have another look tomorrow. Norman

21st Feb 2020, 9:37 pm	#10
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,867	Re: Valve identity help I think the only options are to try the filament as Chris says, then find an old enough radio to try it out in. If you loaned it to an audio aficionado to try out and see if they recognised it by rhythm/pace/authority/granularity and speed of bass, you'd never get it back off them. It's got to be a triode with that number of pins.... did any half-wave rectifiers look similar? David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

21st Feb 2020, 10:14 pm	#11
TowerRadio Hexode Join Date: Mar 2008 Location: Bristol, UK. Posts: 388	Re: Valve identity help With the valve fairly cold breath on it ,may reveal a faint ID.Les

22nd Feb 2020, 10:16 am	#13
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,557	Re: Valve identity help PX25s are significantly taller....

27th Feb 2020, 7:52 pm	#14
whiskas Octode Join Date: Mar 2016 Location: Knutsford, Cheshire, UK. Posts: 1,495	Re: Valve identity help I also think it's a PX4 __________________ ...where on earth did that spring/screw go??

27th Feb 2020, 7:57 pm	#15
Norman Raeburn Heptode Join Date: Feb 2008 Location: Leven, Fife, Scotland Posts: 823	Re: Valve identity help I am fairly sure it’s a PX4, with 4v heater it draws about 950ma. I have a Taylor valve tester and will give it a go and see how it tests. I will report back with the results. Norman

11th Mar 2020, 6:17 pm	#16
Norman Raeburn Heptode Join Date: Feb 2008 Location: Leven, Fife, Scotland Posts: 823	Re: Valve identity help Hi Folks, To bring this to a conclusion and after repairing my valve tester I have the following results. I don't know how well valve testers compare to book figures. I have the following result, PX4 mutual conductance reads 4, book states 3.5 I also have a PX25 mutual conductance reads 1.5, book states 4. Is this likely to be duff or is it a case of it may work ok in something. Looking forward to your opinions please. Norman

11th Mar 2020, 6:56 pm	#17
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Valve identity help Sounds like a good PX4 And a tired PX25 The PX25 will probably still work to some extent in a single ended application and look the part at least. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O