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Thursday, June 11, 2020

Tube of the Month : The 955


Here is another Acorn tube, the 955.

Last month we had with the 957 the second acorn tube in the tube of the month series. So far only directly heated acorn tubes had been shown. The 955 is an indirectly heated variant.

The 955 is an indirectly heated triode with an amplification factor of 25. It has a plate resistance of about 13kOhms which results in a transconductance of 2000 micromohs. The heater is operated at 6.3V and consumes 150mA. The complete set of technical parameters can be looked up in the RCA data sheet. The 955 is another rather strange tube which is long forgotten, especially since the acorn type tubes were never widely accepted. They probably mostly found some use in military applications in RF equipment. The difficult to find sockets make these tubes quite uninteresting for current day amplifier builders. The 955 is the last of the 3 different acorn type tubes I have in stock. So let's have a look at it in detail.

As always we start with the plate curves:

And compare them to actual curves from a tube sample:

Typical curves as can be expected from an indirectly heated triode.

Now some photos of my small stash of different 955 triodes, starting with RCA.

RCA 955 in military packaging:

Another one:

955 made by Hytron:


Arcturus 955:

The box is still completely sealed, so I am not opening it.

A Raytheon 955:

This one came in a neutral box without any manufacturer marking:


And lastly some photos of a 955 in operation.

What a beautiful little gem!

Best regards