SET vs OTL

Paul,

As I noted in my post, I've never gone the really low power output route, so I wasn't commenting on any of the 45 tube designs. OTOH, you mentioned the 211 tube as well. I use this as the default tube in my Cary 805s specifically because the slightly "darker" top end (vs. the 845 output tube alternative) emphasizes the warmer tonal balance of the amp. When the 845 is in service in the Cary, it, too, is warmer/lusher than most amps I've used, but closer to neutral.

I'm sure that tonal balance of most SET amps varies with the impedence curve of the speaker being used, so my observations are qualified by that fact. In actual use, my SET amps have produced pretty consistent results, regardless of the speaker; deep bass is diminished, mid-bass performance is strong, midrange lovely, highs are airy but a bit rolled off. (To be honest, I no longer hear the roll off at the high end - probably one more 50th birthday gift). Dynamics are surprising, almost always exceeding expectations for the power output. However, IME (which -to be clear-excludes the 45 and similar very low output designs), SETs definitely tend to be warm and lush.

Are OTLs more accurate to the source? More linear across the frequency spectrum?

Martykl, if there is one maker of SETs that could be called LUSH, it's Cary. Even their 2A3s are lush, which I'd have thought impossible to do.

You're description of SET bass is especially off in regards to the 45, by the way: very, very tight low end, NO exaggerated mid-bass at all. In fact, they're rather like Ralph's OTLs in that aspect.

No triode is as clear and direct as the 45 IME. I may have mentioned the 211 in the same breath - it's still not nearly as see-through - not in amps I have experience with anyway. (Ongaku? Maybe. Cary? Even less than the Consonance 211s I owned.)

Like you said, 'lush' is not necessarily bad.

Ralph, I didn't realize your OTLs have only one gain stage. I learned something. I may need to try one again.

Paul, I like the type 45 tube a lot too. Not many speakers that will work with a 45 SET though. I am using a set of Coral Betas, which are fine as long as you don't expect any volume.

Larryi, We've been doing this over 30 years now and all our amps have had a direct coupled output. We've seen many tubes fail in that time. So far, we can still count the number of times that a power tube failure damaged a driver on one hand. In all the cases but one, alternative power tubes had been installed in the amp. So it appears that the amp is quite safe. All of our amps except the big 500-watt unit do not use a servo circuit (we installed one in the big amp, but for convenience only). They are quite stable, and simply don't need a servo. The key is controlling the power tubes, something that you would **think** would be common sense, but it is an issue in a lot of designs. That is one of the reasons why our amps have been so reliable over the years (the other being that the amp does not need negative feedback to work).

Martykl:

Gotta side with Paul on this one. My Wyetech Sapphire monoblocks use two 300Bs in parallel per side (18 wpc) and sound exactly like Paul describes: "crystal-clear, just right, completely natural", and certainly not lush. And these are 300Bs! And they drive monitors with a wild impedance swing as well.