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955 as Paramour driver (long)

Posted by cvandyke on January 26, 2006 at 19:10:23:
I recently changed the driver in my Paramours from a 12au7 (stock is 12at7) to a 955, a small, oddly shaped indirectly heated triode with an Rp of about 12K, mu about 25. These tubes are ofter referred to as "acorn" tubes which I think is a reasonable comparison. The socket is also odd and is a ceramic ring.

Physically, the switch turned out to be much easier than I thought it would since the mounting holes on the socket matched up to ones for the old 9 pin socket so no drilling is needed. I opted to mount the socket upside down so that the tube must be inserted from below. I did this so that the terminals would be harder to touch. The top of tube ends up about 1/2 inch above the top plate when it's installed. I see 2 problems with this set up:
The tube can be pushed down and out by the curious or by accident and the hole is certainly big enough to get a finger down by the socket terminals (OUCH! as voltsecond would say). I plan to mount some sort of screen to prevent this.

I think gravity/vibration may eventually push the tube out; I'm going to try to rig a "retaining wire" connected to the bolts securing the socket

Image from below socket: http://home.earthlink.net/~kawcvd/paramour_955_bot.jpg

The cathode resistor was changed to 1.2 K ohms as suggested by Paul Joppa (link below). The voltage across the cathode resistor was 5 VDC for both paramours and the plate voltage measured at 198.2 and 199.6 VDC (CCS upgrade is installed). The grid stopper is still the stock value but had to replaced anyway since the desoldering left the original too mangled to re-use.

I certainly think the 955 is a nice driver tube, and easily betters the 12au7 - I can't really compare to the 12at7 (the 12au7 might sound better if the current could be increased). The sound seems fuller and more musical. Visually, I find the tiny 955 is a nice contrast to the large 2A3. I've bought a number of acorn tubes and I have to say they're as cute as a vacuum tube can be.