This report details measured data for various types of tubes.

In the data shown here, the "dual" tubes, e.g., 12AX7 were run with
BOTH sections paralleled. Results for the tube's single section were
about 3 dB worse, which is not a surprise. In the table Rp was the
plate resistor (not the tubes plate resistance) and Rk the cathode
bias resistor. The supply voltage was about 180 volts. Heater voltage
for "phono" noise for 12AX7 and 12AY7 was 5.5 volts, all others was
6.2V. This seemed to produce the best performance. Included in "6DJ8"
was 6922 and 7308, included in 12AX7 was ECC83, various 'AX7s, 7025.

Also, there is now some data on the "low noise" pentodes (triode
connection mode). Although they do not appear to be as good as the
"best" triodes, remember this is for a single tube, whereas the
"dual" triodes were parallel connected.

Generically the high gm tubes (417A/5842, 6DJ8 etc) seem to perform
fairly well in a "flat" amplifier. The best equivalent input noise
was the 417A/5842, averaging 0.29uV. Of the 6DJ8 types the Amperex
7308 seemed the best, and the group average of 0.35 uV was not too
bad.

For cases where there is a bass boost, e.g., RIAA or NAB equalization,
the red base 5691's produced an average of 0.32 uV, slightly better
than the 12AY7 (6072) at 0.33 uV, with 12AX7 types not too far behind
at 0.45 uV.

There is some variation from device to device. The single quietest
tube WAS one of the chinese 12AX7s at 0.27 uV. This was nosed out
by a red base 5691 at 0.25 uV.

Note the poor performance of the 12AU7s. These were Mullard and
Sylvania, and all were "used". New 5814A bettered this performance
a little, but not by much.

Here's the data........

Type	# tested	Noise flat amp	Noise "Phono"	Rp	Rk
12AX7	    24			0.67	   0.45		130k	1.3k
12AY7/6072  16			0.44	   0.33		 58k	1k
12AT7	    15			0.74	   0.70		110k	1.25k
12AV7	    12			0.60	   0.60		 33k	1.3k
12AU7	     6			1.20	   1.20		 49k	1.95k
5814A	     6                  1.0        1.0           49k    1.95k

6SL7	     6			0.70	   0.65		100k	1.3k
5691 red    12			0.45       0.32		100k	1.3k
6SN7	    16			0.65	   0.72		 25k    340
6CG7	    10			0.65       0.73		 25k    340
5687	    12			0.55	   0.64		 32k	1.25k

6DJ8	    45			0.35	   0.50		 25k	320
6N1P	     4			0.39	   0.38		 25k    390
417A/5842   30			0.29	   0.55		 15k    250

triode connected pentodes:
EF86/6267   10			0.71	   0.61		 62k	1.1k
5879	     5			0.8	   0.65		180k	2k