[Boatanchors] Misical chairs with tubes

[Barrie Smith]

While I had the VT-127A rig on the bench I decided to test all the tubes I have.

So far, I have three pairs that perform well at 72, 75 and 79% efficiency.  All of these tubes have the plain, non-finned plates.

I have two pairs of the tubes the have the finned plates.  Both of these pairs run poorly at 62 and 65%, with hot, hot plates and low power output.

I did re-neutralize each time I changed tubes.

This morning, as a test, I ran the filament voltage up to 6 volts on one set of these tubes and left it there for just over an hour.

I then tested them for power out.  The power out was up considerably and the efficiency was up to 68%.  This was with 5 volts on the filament.

I'm surprised that these tubes would suffer from lack of emission.  They look brand new.

I think I remember that to truely rejuvinate the filament I need to run them at 150% of rated voltage for (?) and then at about 125% for (?).

Does rejuvination last any appreciable lemgth of time?  Is it worthwhile?

73,
Barrie, W7ALW, DN36au,
QRV 6M, 432 & 1296 EME