Does anyone care to ask an amplifier designer a technical question? My door is open.

Ralph, what is OTOH mean? Im a newbee.The cords with diodes make a difference when needed. I think I have been clear and consistant here.

OTOH: On The Other Hand; other slang acronyms you may find handy:
IMO: In My Opinion
IME: In My Experience
IIRC: If I Recall Correctly
YMMV: Your Mileage May Vary
If there are only diodes in the cord, there will be no conduction near the AC crossover point. Electrolytics are thus used as I mentioned prior so that the AC waveform is undistorted. However, it appears you are conflating two different subjects in your comment above.

Your amp draws heaps of current when played hard. Something heavy ga might help a little at full power. At idle Im not so sure. I note the current draw of the M-60 goes up quite a lot at full power testing.

How long can I run an M-60 sinewave at 60 watts into 8 ohms before the tubes get unhappy?

Not very long, but long enough so that organ pedal tones and the like can be reproduced without damage. The tube is linear with grid current.

Is it pure Class D or something else?

It is a good example of class D.

Would very much like your advice on what occurred to me a few days ago with my ss stereo amp.
I own a large stereo ss amp and speakers that both allow for bi-wiring. Four connectors per side and therefore I utilize two separate connectors per speaker cable per side ( four in total on each speaker and amp side). i normally connect two positive and two negative to each respective amp terminal and speaker terminal...left and right. A few days ago, I was re-inserting the amp back into the system and was NOT thinking! This time, I connected the amp correctly, BUT I connected the speakers as positive and negative connectors onto wrong terminals! So, what I ended up with was a positive connection and a negative connection X 2 ( per side) at the amp side ( correct) and a positive and negative connection for each terminal at the speaker end...one positive cable on positive, one negative cable on positive, one negative cable on negative, one positive cable on negative. This was done on both speakers!!! I powered up and noticed that I was getting signal only through ONE speaker, the right hand speaker, with no signal from the left hand speaker! What was going on??? Why signal at only one speaker with this bad connection scheme?
Luckily after much head scratching, I realized my mistake and corrected the hook up...and then both speakers were playing fine. Again, any idea as to why i had sound from one channel...and not both or any? Could I have done damage with this bad connection error?
Thanks for the reply.

No damage, and from what I can surmise, due to luck- one of your connections was apparently loose, otherwise neither speaker would have played. Essentially on the non-playing side, it sounds like the output of the amp was shorted. Fortunately you caught it and sorted it out, so no damage to the amp.

This is assuming that the biwire connection on the loudspeaker employs a common connection between the woofer and HF section.

Thanks. The speakers are bi-wirable at the input, so I am assuming that without a connection at the terminal, which I have removed, that there is no common connection between the woofer and the tweeter. ( it’s a two way). Nonetheless, the right speaker did play, just not the left? I also have a REL sub hooked up to the amp, it is left, right and ground at the amp, as both the amp and the REL are balanced designs. I guess I got lucky and didn’t blow one channel at the amp...or worse that and both speakers!