7963 submini applications?

Gents,
I came across a couple 7963 submini frame grid medium mu dual triodes that appear to be successors to the 6DJ8 which are operatable at very low plate voltage for mic preamp applications.  For the experts refer to http://frank.pocnet.net/other/Sylvania/Sylvania-SSFGT.pdf   who can read the charts, etc. 

According to one source they are more linear with higher mu than a 6DJ8 and can operate as low as 30v DC plate voltage for preamp applications for extremely low noise.  I searched the site for any mention of this tube but found none, so if any experts such as PRR, EMRR, etc could peruse this info I'd be curious.  I have not seen any places online where these are available, but would be curious what the experts think about this valve for preamp, etc apps before I search further.

Regards, Nathan

Some other info on this tube-

Sylvania's 1962 publication entitled "Sylvania Subminiature Strap Frame Grid Tubes for Military and Industrial Applications" describes the development of a new line of subminiature tubes as follows:
"The advantages of the strap frame grid are quite well known and are attested to by the steady increase in the number of new electron tubes employing this innovation. The area of growth in the past, however, had been restricted to miniature and larger designs. About two years ago, Sylvania launched a program to develop a subminiature frame grid tube design for the Military and Industrial markets. The results of this program to date are ten new tube types. Each new type, when compared with its nearest conventional predecessor, shows a marked improvement in gain and operating efficiency of both the plate and heater. In addition, the new design offers the mechanical ruggedness, stability and reliability, characteristic of subminiature construction."
The majority of subminiature tubes are downsized versions of existing miniature 7 and 9 pin types which, in turn, were smaller versions of existing octal types -- for example, the 6SN7/5691 beget the 5751, from which the 6112 was derived. The 7963, while claiming no octal forerunners (as t were no frame grid octal twin triodes), can trace its ancestry to the 6DJ8 family. In fact, with regard to audio applications, the 7963 offers performance in low level audio applications that is superior to all 6DJ8 variants, and to all other subminiature twin triodes as well. In a tube-to-tube comparison between the 6DJ8 and the 7963, the 7963 exhibits:
A) superior transconductance -- 14,000 micromhos for the 7963, versus 12,500 for the 6DJ8;
B) slightly lower plate resistance -- 3100 ohms for the 7963, versus 3200 for the 6DJ8;
C) higher voltage gain -- 40 for the 7963, versus 33 for the 6DJ8.
In addition, the 7963, is more linear than the 6DJ8, as a comparison of each tube's characteristic curves will attest.
Perhaps the greatest advantage the 7963 has over the 6DJ8 is will be found in its reduced voltage requirements. T is a strong correlation between plate voltage and tube noise -- the lower the plate voltage, the lower the tube's noise figure. For line level applications, the 7963 requires no more than 75 volts dc; in most cases, 50 volts is quite adequate. For moving magnet phono, and for microphone preamplifier requirements, 30 to 50 volts dc will do the trick. For moving coil cartridge step-ups, 15 to 25 volts is all you'll need!

Hope it helps, Nathan

Good find.

Can you actually buy these?

> T is a strong correlation between plate voltage and tube noise -- the lower the plate voltage, the lower the tube's noise figure.

?? 1/Gm is often the dominant noise source. Since these tubes are capable of high Gm at low plate voltages, they are great.... but low plate voltage alone is not low NF.

PRR,

I found around 20 7963's at my local surplus store.  Not sure what he would charge for them but he's really ignorant of the going price of tubes that audio guys are interested in.  My guess that other military surplus stores may have these but have no idea of their desirable properties for audio use and therefore don't publicize them.

Thanks for your reply!

-Nathan