SET vs OTL

Atmasphere,

I agree that multiple output tubes is really only a theoretical source of less than perfect sound (my SET has parallel output tubes). I am merely pointing out that "theoretical" concerns can be raised about any design choice.

A friend of mine has a direct-coupled OTL that has performed flawlessly for years. I would worry about some kind of catastrophic failure, such as an output tube shorting. Can that happen and is it a realistic concern? Wouldn't a servo circuit be the best approach to maintaining good sound while assuring safety?

Thanks, your posting are very informative.

I'd strongly disagree with Paul's comments re: SET amps not sounding "lush" vs OTLs.

While my earlier comments re: the "romantic" sound of SET amps were primarily intended to describe 300B SETs (and more specifically the Cary monos I own), I find some elements of this "lush" quality in all of the SET amps I've heard. I would specifically include the Cary 805s I also own, and more specifically include the 805s when used with the 211 output tube.

I have never gone the "flea power" route, so I can't comment on those, but I've heard 300B based amps from several manufacturers and ALL of them sounded warm tonally, so it ain't just Cary. As to OTLs sounding "whitish", I've heard that, too. My early production S-30s could sound this way when paired with the wrong speaker.

Marty

Incidentally, nothing wrong in my book with "lush" sounding amps. That's precisely the reason I own two pairs of SETs.

Marty

Martykl, no properly built single-ended 45 amp is lush in any sense into appropriate speakers.

Have you heard any? Which do you call lush?

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.