Posted this over on the pentode thread but figured I put it here too just so
@SonicTrance knows what a psycho he’s actually dealing with
I’m a sick, sick man. My new Ultrasonic Studios amp hasn’t gotten here yet (soon though!) and I have been planning my next amp already. Basically I want a version of what I have right now, a single ended pentode amp. The Dennis Had Inspire KT88 Firebottle is a remarkable amp. Single ended pentode with auto bias and by changing rectifier tubes you can use output tubes ranging from 6f6 up to kt88. Power output ranges from 3ish watts up to a whopping 10 or so. I want the same amp but designed around lower power tubes like the kt61, 6aq5, etc. that max out around 250v. To help get around the low power I would want it to be a parallel single ended with two or three(!) tubes per side. Of course I would want switchable, or even better variable, heater voltages. And if I’m greedy I would like to switch between ultra linear and pentode. What the hell, why have a cheap output transformer?
The thing is, single ended pentode amplifiers are tricker to design than triode. You need to have regulated screen supplies. And while feedback is optional with triode amps, it is essential with pentode ones. There are many different kinds of feedback; local, global, cathode, Schade, etc. Some of those require careful pairing with the output transformer. Getting out of the engineering mindset and into the artistic one is a rare skill for amp designers but it is a necessary one when it comes to balancing feedback schemes. Dennis Had (he’s the one that founded Cary amps and is responsible for the popularity of single ended amps in the US IMO) has the formula nailed. Not only do his amps sound amazing, they sound amazing with a variety of tubes. The trouble is I don’t think I can convince him to build to my specs. And even if I could I’m not sure I could afford it lol.
Anyway, yeah, the thought has crossed my mind lol.