Half Power Switch

[TIMBO]

Hey guys,
I've got 100w (4x6L6GC) build I'm doing and want to add the half power switch.
I've checked out the silver jubilee triode/pentode and that will be my second option.
So I have wired a rotary switch that will disconnect the cathodes of the two outer 6L6's and change the secondary taps to suit ( 6L6x4 - 2K/6L6x2 - 4K)
Will having the two 6L6's NOT connected at the cathodes do damage to them?

[sluckey]

no

[TIMBO]

SWEET!!!! 

[stratomaster]

I've seen some designs add a large-ish resistor, 10k or so, to the cathodes instead of leaving them disconnected.  I guess the theory is that it's better for the tube to bias it cold to cutoff instead of leaving it floating.  I have no idea whether this holds any merit though.

[tubeswell]

I've seen some designs add a large-ish resistor, 10k or so, to the cathodes instead of leaving them disconnected.  I guess the theory is that it's better for the tube to bias it cold to cutoff instead of leaving it floating.  I have no idea whether this holds any merit though.

For fixed bias, the bias is provided via negative voltage on the grid. So opening the cathode won’t make any difference there.

For cathode bias, it won’t make any difference either, because the grid is grounded anyway and the cathode resistor will limit current surge when the switch is closed. Besides that, the other pair of ‘always on’ tubes will absorb any spike because they’re in the same power amp circuit.



A bigger challenge is switching the load resistance. (Which could be facilitated by switching parallel speakers in/out, while always keeping a secondary load connected).

[kagliostro]

Secondary impedance to be switch = big current = big switch contacts

I'll prefer to simply switch to ground the signal that feeds a pair of tubes, half power without any other mod

Franco