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Tuesday, May 31, 2022

Tube of the Month : The 3C24

Hi!

This month we have another rather unusual tube. The 3C24:



The 3C24 is a transmitting tube developed for Class B audio amplifier or modulator use or for Class C RF amplifier or oscillator service.

It is a directly heated triode with thoriated tungsten filament on an UX4 4 pin base. Only the two larger diameter base pins are used for the filament connection. The grid is brought out of the side of the tube and the plate on top. This provides good high voltage insulation for the max plate voltage of 2kV. The filament operates at 6.3V and consumes 3A. The tube is rather small for a transmitting tube with an overall height of about 11cm including base and top pins and only 6cm height of the glass bulb and 3.5cm diameter. For all technical information please refer to the EIMAC data sheet. The tubes shown below are kindly provided by Josef from Vienna who has a good collection of some crazy tubes.



Starting with a 3C24 in military packaging made by North American Philips Co. (Norelco). 





The tube also has the military type number VT204 printed on the base.




The plate and grid connections:












A 3C24 made by Lewis Electronics:







Another Lewis 3C24 in different packaging:








The next one is from a rather unusual brand.




I never came across this brand name before.





The tube bears the HK (Heinz Kaufmann) logo which to my knowledge was a rebrander.







And lastly an EIMAC 3C24:




Due to the structure of the tube with the plate enclosed on the top, only some glow at the bottom is visible when the tube is in operation:




A shot from below where the unique filament and grid structures are visible. The filament is a spiral around a central rod with the grid as cylindrical cage around it.




I hope you enjoyed the tube of the month presentation. Thanks to Josef for lending the tubes to me.

Best regards

Thomas




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4 comments:

  1. WntrMute2June 12, 2022 at 10:45 PM

    When plate voltage is applied, there is substantial glow from the cathode. These are my 3C24 mono-blocks.
    https://imgur.com/uBtQTDU
    https://imgur.com/EkY32D6

    ReplyDelete
    Replies
    1. AnonymousJanuary 27, 2023 at 7:32 PM

      Hi,
      can I ask what at voltage and current you are using the 3c24 ? Also, which Monolith opt are you using?

      Delete
    2. WntrMute2February 21, 2023 at 9:38 PM

      Hello, thanks for your interest. I am using the Monolith Magnetics S-11 Summit.
      The voltage is 405 B+ mA 60. Here is a link to the build thread. https://hifihaven.org/index.php?threads/3c24-new-build.7652/

      Delete
    3. NigelMay 28, 2023 at 6:18 AM

      I assume you mean the glow is within the 3C24's.
      In that case it's commonly a symptom of gas within a high vacuum valve, possibly through leakage along glass-metal seals, possibly from outgassing due to excessive heating.

      The tantalum anode of 3C24 can self getter at normal operating temperatures where it would show cherry red to orange at the rated 25W depending on external cooling. The 3C24 must have heat dissipating caps on both anode & grids terminals to keep seal temperatures within spec.

      Yours appear to be running very hot indeed or is that a quirk of the photography?

      Delete