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Tuesday, May 31, 2022

Tube of the Month : The 3C24


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


Monday, May 9, 2022

SE 300B Mono Blocks


The single ended 300B amps with 801A driver are the most popular among my amps this year.

Here some photos of another recently shipped pair.

These amps will be adequately driven by this 10Y line preamplifier:

Finished in the same smoked eucalyptus wood.

Some more pics of the amps:

Best regards