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Author Topic: The 3D6 Loktal beam pentode for AF and RF to 6 meters.  (Read 1180 times)
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Patrick J. / KD5OEI
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« on: October 09, 2020, 02:27:09 AM »

A box turned up with a bunch of NOS 3D6 tubes. It wasn't familiar to me but that's likely because it's a Loktal base which is not as popular as before my time. The Loktal has some advantages and was advanced for its time in that the pins come through the envelope like miniature and compactron types, rather than leads coming through as in Octal and 'pillar base' 4-5-6-7 pin tubes that have separate bases with soldered pins. The thing I don't like about loktals is the force required to put them in and take them out.

I mostly see Loktals in antique radios including some old communications gear where there was a mobile version. Where do others find Loktals?

The wafer type sockets are only about $3, Chinese ceramic $5-10. Russian shielded military-looking ceramic sockets $3.

In some ways the 3D6 is like the Octal 3Q5 on steroids. It gives 30mA cathode current vs. 12mA, and tolerates higher plate voltage. The 3D6/1299/VT-185 is interesting in that it has a 4.5 watt plate dissipation.
It's rated 1.4W ouput at 50MHz Class C.
It also has audio ratings of 600mW output in Class A. Hopefully it might make 2-4W in push pull AB. AB2 seems possible since it's rated for class C. The grid should stand up and be counted.

It's designed for portable equipment, and the center-tapped filament runs on 1.4-1.75V or 2.8-3.5V. The data sheet ratings are specified at the lower end of the range. Plate voltage given in the operating conditions data is 90-150.
https://frank.pocnet.net/sheets/127/3/3D6.pdf

Anyway it could be the ultimate QRP power amp using a flashlight battery and a stack of 9-Volts and off we go.

I just wish I had more time to experiment with these obscure and interesting things.
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