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Old 16th Nov 2020, 2:53 pm   #1
agardiner
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Default 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.
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Old 16th Nov 2020, 3:58 pm   #2
Cobaltblue
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Default 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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Old 16th Nov 2020, 4:00 pm   #3
agardiner
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Default 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.
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Old 16th Nov 2020, 4:44 pm   #4
cathoderay57
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Default 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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Old 16th Nov 2020, 5:07 pm   #5
agardiner
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Default 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.
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Old 16th Nov 2020, 5:11 pm   #6
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Default 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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Old 16th Nov 2020, 6:28 pm   #7
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Default Re: UCH21 / UBL21 / UY21 Valve help please

Quote:
Originally Posted by wave solder View Post
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.
Can't be that as the new old stock one didn't show any shorts.
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Old 16th Nov 2020, 11:02 pm   #8
cathoderay57
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Default 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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Old 16th Nov 2020, 11:09 pm   #9
agardiner
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Default Re: UCH21 / UBL21 / UY21 Valve help please

Thanks for the suggestions.

Will carry out some tests and report back.

Adrian.
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