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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
pryso
1,501 posts
 
bsimpson, in case you may still be following your thread.

I've owned a pair of AtmaSphere monoblocs and spent time with a few different Joule Electras.  From that experience I can offer two considerations.

First is the appropriate match with speakers.  That is a question of both power and load impedance.  Proper mating with lower than 8 ohms can be problematic.

Second is the issue with heat.  More output tubes may be required per channel to drive lower loads with OTLs.  My AtmaSpheres had 10 outputs per channel to produce 100 watts which I attempted with 4 ohm speakers.  They put out more heat than similarly rated transformer coupled tube amps.  But with less demanding (i.e. complex) music at reasonable levels they were magical.

That was all some years ago and now I look forward to auditioning the ZOTL 40s that lancelock recommends. 
mikelavigne
1,274 posts
 

my OTL experience is now more than 10 years ago, but the OTL magic is still a guiding light in my sonic compass.

in 2001 i was moving away from Wilson WP6’s and top level Mark Levinson #32 and #33 mono blocks. i looking for a more involving and musical presentation and purchased Kharma Exquisite Reference 1D speakers and starting searching for an amp to go with it. tried a few and then had the opportunity to demo the Atma=sphere MA2 Mk2.2’s in my room and really liked it. i was ready to pull the trigger but then had another opportunity to try the Tenor 75 watt OTL mono blocks. ok; here was a modestly powerful amplifier but this one had a fire in the mid range and was linear top and bottom. it seemed like a direct connection to the music. so i purchased the Tenors and had a 3 year love affair.

like some other love affairs, it was painful too. the darn Tenor would explode on a regular basis and take out drivers in the Kharma’s. that direct sound and lack of transformers did have it’s dark side. so I ended my love affair.....but looked around for a something else that could be similar but was reliable.

i ended up with darTZeel NHB-108 solid state which combined that fire in the mid range and transparency of the Tenors, but also had the solid state attributes of lower noise, more authority, and reliability.

back to the Tenor OTL’s; eventually Tenor went bankrupt; but the good news is that another group bought the assets and raised it from the dead, and the 75 watt Tenor OTL’s got their design cleaned up and did become reliable......and i would strongly recommend a set if you can find one (and make sure it was built after 2005 or upgraded.

it’s a magical amplifier. or get a darTZeel solid state and never look back. i did.

atmasphere's avatar
atmasphere
7,068 posts
 
@mikelavigne ,
back to the Tenor OTL’s; eventually Tenor went bankrupt; but the good news is that another group bought the assets and raised it from the dead, and the 75 watt Tenor OTL’s got their design cleaned up and did become reliable......and i would strongly recommend a set if you can find one (and make sure it was built after 2005 or upgraded.
This statement seems to be incorrect. To the best of my knowledge they only make solid state amps; I'm sure we would have heard about it if they still made OTLs.

FWIW the MA-2 Mk2.2 dates from about 17 years ago...  and in the intervening time we have managed to make some progress :)  The current incarnation of the MA-2 is Mk3.3. People have described the improvement as a 'transformation'.
kdude66
1,198 posts
 
Hello All,

I have the Zotl 40 paired with the MZ2S preamp and after 4 days of use,only playing my worst sounding recordings as a test I find they all sound better than I've ever heard them.I'm using Mullard XF2's from 1966 and haven't used the gold lion Kt77' yet.

More evaluation time needed to truly sort this out,but I do believe I have found a pairing that I will be happy with for a long time.

Best,
Kenny.
mikelavigne
1,274 posts
 

This statement seems to be incorrect. To the best of my knowledge they only make solid state amps; I’m sure we would have heard about it if they still made OTLs.

FWIW the MA-2 Mk2.2 dates from about 17 years ago... and in the intervening time we have managed to make some progress :) The current incarnation of the MA-2 is Mk3.3. People have described the improvement as a ’transformation’.

Ralph,

Tenor makes hybrid tube amps (an update to their Hybrid 300 mono blocks I owned briefly in 2004) now. not sure about any other products. however; back in 2005 a group of investors did purchase the assets of Tenor and did redesign/update the tubed OTL amps and sell them as a current product for some years. there are still a few out there new for sale but not sure it’s a current product anymore.

regarding my personal Atma=sphere MA2 experience; if you read my post it says this happened in 2001, 16 years ago. i’ve had many positive things to say about you and your products over the years and just because i preferred the 75 watt Tenor OTL’s back then, does not change the fact you make great products and take great care of your customers. i’ve heard your more recent products many times at shows and they are as you describe.

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