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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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16th Nov 2020, 2:53 pm | #1 |
Octode
Join Date: Sep 2020
Location: Thetford, Norfolk, UK.
Posts: 1,743
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UCH21 / UBL21 / UY21 Valve help please
Hi,
So I have a valve emission tester, which I am familiar with using, and indeed I have made up an adapter from an octal base to crocodile clips for older valves that don't plug straight in. Over time you get a 'feel' for valves which are not listed in the book for it, as to whether the emission is OK or not. Back to the valves above; I have just completed restoring a Philips set which has the valve line up of 2x UCH21, UBL21 and UY21. The UY21 was indicating short circuit on my tester, but I ended up having to replace all 4 valves. The question I have, is what am I missing in understanding these particular valves, as I cannot get any emission at all on my tester. None. And this was with new, old stock valves. Can anyone shed light on this anomaly for me? Many thanks, Adrian. |
16th Nov 2020, 3:58 pm | #2 |
Moderator
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,878
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Re: UCH21 / UBL21 / UY21 Valve help please
You don't say what kind of valve emission tester you are using.
Were you setting the filament voltage correctly? The UBL21 for example has a 55V filament. Cheers Mike T
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16th Nov 2020, 4:00 pm | #3 |
Octode
Join Date: Sep 2020
Location: Thetford, Norfolk, UK.
Posts: 1,743
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Re: UCH21 / UBL21 / UY21 Valve help please
Hi,
I have a Micronta T31 tester. Yes, I set the filament voltage correctly. I have the data for the valves. Thanks, Adrian. |
16th Nov 2020, 4:44 pm | #4 |
Nonode
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 2,388
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Re: UCH21 / UBL21 / UY21 Valve help please
Assuming that the tester works OK on at least one other valve type, then the most likely explanation is a mis-connection of one or more valve pins. I'm not familiar with this valve tester as I have an Avo VCM163 but even with that you have to be careful with the valveholder pin numbering which differs in some cases from the numbering orientation in valve data books. There is nothing special about the U valve types mentioned. Do the heaters illuminate? Cheers, Jerry
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16th Nov 2020, 5:07 pm | #5 |
Octode
Join Date: Sep 2020
Location: Thetford, Norfolk, UK.
Posts: 1,743
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Re: UCH21 / UBL21 / UY21 Valve help please
Hi Jerry,
Yes, the filaments do light. And the continuity is correct on the expected pin. Also, as I said in the original post, it did identify a short in the original rectifier valve. Hence my confusion. All other valves test OK, but I have to admit it is the first time I have used this particular socket. Perhaps there is a minor wiring fault in the socket concerned. I might try connecting one up with the alligator clip adapter I have made to see if i get the same results. Regards, Adrian. |
16th Nov 2020, 5:11 pm | #6 |
Hexode
Join Date: Feb 2007
Location: Chesterfield, Derbyshire, UK.
Posts: 483
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Re: UCH21 / UBL21 / UY21 Valve help please
If pins 2 and 7 are transposed with a UY21 then you will get a dead short because pins 2 and 4 are Anode and pin 7 is cathode.
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16th Nov 2020, 6:28 pm | #7 |
Octode
Join Date: Sep 2020
Location: Thetford, Norfolk, UK.
Posts: 1,743
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Re: UCH21 / UBL21 / UY21 Valve help please
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16th Nov 2020, 11:02 pm | #8 |
Nonode
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 2,388
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Re: UCH21 / UBL21 / UY21 Valve help please
Why not measure the voltages at the various pin sockets on the empty valve holder? Should give you some idea of what is amiss, and whether you have cross-connected something or an open circuit wire or joint. If the heater lights up you have already eliminated that, so are there appropriate voltages on the anode and grids and a path to valve tester ground return from the cathode pin?
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16th Nov 2020, 11:09 pm | #9 |
Octode
Join Date: Sep 2020
Location: Thetford, Norfolk, UK.
Posts: 1,743
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Re: UCH21 / UBL21 / UY21 Valve help please
Thanks for the suggestions.
Will carry out some tests and report back. Adrian. |