Vacuum tube amplifier with selectable power devices

[glassesnvests]

I met Jackson Ampworks' Brad Jackson over the weekend and had the chance to play his new McFly amp. Really incredible little amp! Uses 6SN7's in the pre, a swith to get either tween or BF tones, and has the nifty feature of playing through 6V6's for ~20watts, 6L6's for ~40 watts, or both simultaneously for a claimed 70 watts. Which got me curious. I found this patent by Randall Smith (https://www.google.com/patents/US5559469) that outlines a way to have two different types of power tubes, cathode biased, and switch between one or the other or both at the same time just by lifting the cathode from ground.


What design considerations would this entail? Is it practical? I'm thinking of trying out something like this with the proper think-through.
I'd think that output impedance would definitely be an issue. That along with PT ratings for heater current, plate current, etc.
Are there any other known ways to accomplish this?

[kagliostro]

Are there any other known ways to accomplish this?

Oh YES, there are

one way is to have all the tubes always connected with an dequate OT primary impedence and use two separeted PPIMV,

one for the 6V6 and the other for the 6L6

this way you can select any % of mix between the two tubes

as example 22% of 6V6 + 44% of 6L6, but also 100% 6V6 + 100% 6L6

this way your OT must be able to afford the power of the entiere set of tubes

one other way will be to arrange the PPIMV as rotating it CW you increase a type of tube power and decrease the other

as an example rotating CW you can obtain till 100% 6V6 and 0% 6L6 and having the PPIMV set on the middle (12 o'clock) you have 50% 6V6 + 50% 6L6

this way you can use an OT rated for less W

K