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What's your OTL tube amp experience and suggestion?

Are OTL amps in general much less reliable due to their nature, or due to the implementation quality, or both?

Perhaps this has been discussed a zillion times in the past.   Perhaps, however, makers have now improve on past experience?  So it could be worth re-visiting.

My past encounters with OTL tube amps are among the most negative: Wonderful (but never great) sound during the brief period that they work.  Otherwise, major fire hazard.  Overheating, red hot plates, sparks, consistently toasted fuses, burning smell, you name it.  My past OTL amps are like crying babies on an changing table - don't you ever walk away from an arm's distance.   The used market seem to reflect such as well --- way more 'as-is for parts' or 'totally refurbished' units than reliable 'used' units that rarely need service.

Beg your pardon if it's just my poor judgement that keep getting the lemons.   What's your experience, and tips to keep OTL amps up and running happily?


bsimpson
botlaudio's avatar
botlaudio
3 posts
 
Thaluza
I have a Joule-Electra VZN 80 and I have never had any of the issues you speak of .
Did you bias the tubes including the driver tubes. It was easy to tell if an output tube was going bad it would not hold Bias. The joule OTL are the best sounding of any I have owned or demoed .
ozzy's avatar
ozzy
7,486 posts
 
Atma-Sphere M-60 3.3 with the upgrades Ralph offers.
Plus I use dual Zero’s with my 8 ohm 90+db Hi-Eff speakers. I can play the music as loud as I once did with my Pass Labs X350-5.
And... the music is so smooth and perfect... No turning back
I am also using Russian output tubes and Sophia input tubes.
ozzy


dragon_vibe
430 posts
 
Ozzy, have you experimented with the RCA Output Tubes?


rusty_jefferson
8 posts
 
To answer the original questions, there can be reliably and potentially safety issues with OTL amplifiers, especially early designs.  The best implementation I've seen are the Berning ZOTL amps.  They are safe, and reliable.  Most won't require retubing for years, or decades. They have autobias, and protection circuits, plus very low output impedance,  making them very versatile in matching them to a wide variety of speakers.

As well as the models available on his website, or licensed by LTA, David has a collection of small, lower power models available he doesn't promote on the website that includes  300b SET and PP, 6b4 SET and PP, 845 SET, etc. All the models I've heard (and owned) sound outstanding. 
atmasphere's avatar
atmasphere
11,841 posts
 
@rusty_jefferson 

Our (Atma-Sphere) claim to fame is we made the first reliable OTLs. That was in 1976. I don't know of any OTLs that were safety issues, including early designs. I've heard this said before, but as far as I know its some sort of myth.

FWIW, the Berning amplifier is not an OTL. It is a uniquely different design and does employ an output transformer (unlike an OTL; 'OTL' stands for Output TransformerLess).
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