Tests performed by Herbie's Audio Lab with Amperex 6922 PQ input tubes yielded these glass bulb temperatures:

Bare tubes: 57.2 C (135 F)
With Pearl Tube Coolers: 68.3 C (155 F)
With brass Tube Anchors: 76.1 C (169 F)
With Duende Criatura Tube Rings (placed near top of tubes): 57.9 C (136 F)
With UltraSonic Damping Instruments: 56.6 C (134 F)

Glass temperatures of Svetlana EL34 "Winged-C" output power tubes:

Bare tubes: 114.7 C (238 F)
With Pearl Tube Coolers: 110.3 C (231 F)
With UltraSonic Damping Instruments: 114.1 C (237 F)

All tests were conducted with Sonic Frontiers SFS-80 amplifier in ambient room air (74 F) with 60 minutes warmup. Results are averages of four tubes of each type tested. Amplifier tube bias set at mid-line 50 Milliamperes.

Glass bulb temperatures vary considerably at different locations of the bulb; all measurements were taken at the same relative locations on each tube.

(Re-tests conducted to verify these results showed a margin of error of approximately +/- 1C with small-signal tubes and +/- 3C with output tubes.)


Cool Tube Dampers by E.A.T.

Tests performed by Herbie's Audio Lab with Amperex 6922 PQ input and driver tubes, SFS-80 amp, semi-enclosed space, ambient room air (74 F):

(degrees F.) Tube 1 Tube 2 Tube 3 Tube 4
After 45 minutes: w/damper: 146.7º
w/o damper: 127.1º
w/damper: 152.5º
w/o damper: 143.4º
w/damper: 152.0º
w/o damper: 142.8º
w/damper: 147.8º
w/o damper: 127.2º
After 90 minutes: w/damper: 156.9º
w/o damper: 129.6º
w/damper: 166.0º
w/o damper: 143.1º
w/damper: 169.6º
w/o damper: 141.8º
w/damper: 159.0º
w/o damper: 131.3º