This might be of interest to others with similar old rigs -

The SBE-33 uses a 12DQ7 ($4.50) Driver and a pair of 27GB5's ($5.10 + $5.10)
in a push push configuration. HV is about 460 vdc on the plates.

The question is like most - 95% of my time is spent listening. Seems like a
waste of energy to lite up those tubes.

So I was thinking about putting a switch in back to turn filament voltage
ON/OFF. Wondering if leaving the HVDC ON will strip off the electron space
charge even if I am not transmitting but still using BIAS voltage. ON some
old hybrid Kenwoods and Yaesu's they had filament and high volt switches in
the front panel.

Another problem is the VFO would drift up due to the heat of the tubes so if
everything was cold the dial would be off 5 to 8 kc. This is a tiny rig 0
the VFO is 8" from the Final Section - it's pretty stable after 20 mins.

Thinkin about the cost of tubes ($14.70) it might not be worth moding it -
still what other problems might pop up?

I still might prototype ot anyway to see what happens...