I haven’t gotten the time to complete the testing on the Curly Maple yet, but I did receive a couple of tubes for which I’ve been waiting so I can try them in the new amp.
The bias point for the Curly Maple, while chosen specifically for the 6V6, supports operation of the entire 6V6 and 6L6 families of tubes as well as the 6F6. The 6W6 also worked out well in the Marblewood, but my fear is that the Curly Maple may be a little to hot for the 6W6 tubes.
However, it was suggested to me that I try out some 6K6 power tubes. The ones I ordered finally arrived.
The 6K6 is, like the 6F6, not a beam power tube but a true pentode. Now pentodes behave a little differently than beam power tubes in UL typologies. But, after looking at the data sheets, I decided I would give them a try in the curly maple. My only real concern is that the maximum plate dissipation for the 6K6 is only 8 watts. However, if the power dissipations are within specification, I’ll take a few measurements and see how they sound. I may also give them a try in the Marblewood as well.
As always, questions and comments are welcome.
After looking at a few data sheets:
As you said plate dissipation of a tad over 8 watts (8.8) – kind of “light duty”
Has pretty high THD – up to 15% in SEP operation, don’t know what that means for SEUL operation.
And, most of the sheets seem to steer you to 250V plate voltage.
As for the 6V6 – there is a lot more tube in there than the data sheets suggest. Some guitar amps run 6V6’s under conditions that should cause the tube to explode, but they don’t – they keep booking right along.
After working with the characteristics curves, my concern is that the 6K6 is going to bias around 45mA to 48mA with about 280V on the plate. This corresponds to about 13W of plate dissipation. This is way too hot for the 6K6. I might even do a little prototype characterization before I plug it into the amp. My current feeling is that the cathode bias resistor may be too low for the 6K6 at this voltage level. We’ll have to see once I get the Curly Maple 6V6 characterization complete.
Interested to hear how it goes! I’ve used 6K6’s in place of 6V6’s in a Bottlehead Moreplay – they sounded quite good. I’ve since found some JAN Sylvania 6V6’s that sound even better in it. I just recently finished an amp based on your spalted alder design – it sounds great! Will be doing some testing soon.
Looking forward to hearing your thoughts. I see these tubes in old radios that people no longer want, and wonder if they could get a new purpose. Your pair looks great!