Using a standard pentode-tetrode as output "space-charge tube" any ideas-experiences?

[Fuzzbrain01]

My two cents:

If you're looking for novel ways to hook up tubes for low-voltage, higher current operation, try Steve Bench's site:
//members.aol.com/sbench101/ specifically his discussion of inverted operation (swapping grid and plate connections). He gives examples using 6AS7 and 5687. The drive voltage requirement is kinda high, and you won't get any voltage gain, but it seems that you can realize substantial "plate" currents at low (<50V) voltages. He also mentions using beam tetrodes in this mode.

When I first read Steve's pages on inverted operation, I was inspired to buy several 12K5's. I thought this might be a good candidate, since the G1 space charge grid is designed to dissipate 1W, as noted above (and they were cheap at the time!). Alas, real life intervened, and the 12K5's have joined their idle comrades in the tube box, awaiting a day when I can come back and play at my workbench for a while (sigh!).

Have fun, and good luck!
Mike

[capritar]

I just finished a single 12k5 output tube amp,and im pleased with its sound. I want to get more power and headroom, in a second version, maybe stereo, so, I intend to run at 24 to 30 volts. The 12AL8 tube has also been used for low voltage designs, i may give that one a try also. About cascode circuits, that is something i think is worth a try, i have to find some cascodes close enough to these tube values though. I lost the link for the Pass tube/jfet cascodes, does anyone have them? Ill post all these up when finished and compared in sound. Ill just add that i am enjoying sweet souind out of the little 12k5 as we speak

[Wavebourn]

Even space charge tubes never were used for anything close to hi-fi. Any tube will work on low voltages, but distortions will be horrible, and output power will be a fraction of what you spend on cathode heating. Take a bunch of JFETs in parallel if you want good sound. However, if the purpose is to experiment, it is a totally different story. You may solder a bunch of 6AK5 in parallel.