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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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21st Feb 2020, 4:05 pm | #1 |
Heptode
Join Date: Feb 2008
Location: Leven, Fife, Scotland
Posts: 823
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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
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21st Feb 2020, 4:09 pm | #2 |
Diode
Join Date: Aug 2019
Location: Sussex, UK.
Posts: 5
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Re: Valve identity help
Definitely a PX4
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21st Feb 2020, 4:11 pm | #3 |
Octode
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,561
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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.
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21st Feb 2020, 4:40 pm | #4 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,970
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Re: Valve identity help
It certainly looks like a PX4 - nice condition too.
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21st Feb 2020, 4:42 pm | #5 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
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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
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21st Feb 2020, 6:05 pm | #6 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: Valve identity help
The markings will probably be on the opposite side to the label.
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21st Feb 2020, 7:04 pm | #7 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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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!
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21st Feb 2020, 8:26 pm | #8 |
Octode
Join Date: Jul 2004
Location: Evesham, Worcestershire, UK.
Posts: 1,423
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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.
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21st Feb 2020, 8:39 pm | #9 |
Heptode
Join Date: Feb 2008
Location: Leven, Fife, Scotland
Posts: 823
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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
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21st Feb 2020, 9:37 pm | #10 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,902
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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
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21st Feb 2020, 10:14 pm | #11 |
Hexode
Join Date: Mar 2008
Location: Bristol, UK.
Posts: 388
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Re: Valve identity help
With the valve fairly cold breath on it ,may reveal a faint ID.Les
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22nd Feb 2020, 8:03 am | #12 | |
Octode
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
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Re: Valve identity help
Quote:
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.
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22nd Feb 2020, 10:16 am | #13 |
Octode
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,561
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Re: Valve identity help
PX25s are significantly taller....
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27th Feb 2020, 7:52 pm | #14 |
Octode
Join Date: Mar 2016
Location: Knutsford, Cheshire, UK.
Posts: 1,500
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Re: Valve identity help
I also think it's a PX4
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27th Feb 2020, 7:57 pm | #15 |
Heptode
Join Date: Feb 2008
Location: Leven, Fife, Scotland
Posts: 823
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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
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11th Mar 2020, 6:17 pm | #16 |
Heptode
Join Date: Feb 2008
Location: Leven, Fife, Scotland
Posts: 823
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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 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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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.
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