Unidentified tube

Halo radio friends,

I've just got a small vintage tube which I can not identify. It has a 4-pin base and is about 4cm tall in total.

Between pins 2 and 4 is a thin wire of 1.2 Ohm DC-resistance.

Across it there is a second. much thinner wire, connected to pins 1 and 4.

Its resistance I could not measure! Maybe there is open circuit, or the resistance is very high, beyond the range of my multimeter. It could be a sort of current regulator, or a sort of Hot Wire Barretter. Does anybody recognize this tube, or has some idea about it?

Thanks, Dejan

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Hello Dejan,

this appears to be a Thermocouple, apparently burnt out, due to the open circuit between pins 1 and 4.

Best Regards,
Jacob

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Thank you Jacob, That's it !!

I have made mistake by typing: What appears to be the thermoelement is connected to pins 1-3, and NOT to 1-4 as I wrote. Sorry,

Best regards,

Dejan

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Hello Dejan,

Judging from the exterior of your thermocouple tube and the resistance of 1,2 Ohm for the filament section, it very likely is a Philips or Valvo TH5.

See TH5 Philips.

I once used such a thermocouple to build a RF miliwattmeter, whereby the RF source heated the filament, thus generating a thermal voltage across the thermocouple. This voltage was a measure for the RF power. The connections have to be kept very short in this design in order not to introduce unwanted resistance at RF frequencies. The nice thing of such a device is that you can calibrate the instrument with a simple and accurate DC source.

These thermocouples are very delicate and vulnerable. I still have a few species of the Philips TH1, TH2 and TH5 in my collection.

Best regards,

Gidi

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Thanks Gidi,

A nice idea to make RF miliwattmeter, but it seems to be an opencircuit in the thermoelement line - should it be any resistance or voltage at room temperature. I could not measure any!

Best regards,

Dejan, YU1NGL

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If your thermocouple tube really would be a TH5, the resistance of the thermoelement section should measure 3,5 Ohm. See table.

Unfortunately your thermoelement certainly is an open circuit.

Regards,

Gidi

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