Did you do any intermediate circuit tests along the way? Very difficult to correct in a tightly packed finished project.
Yes, indeed @jhstewart9 : it's a modular construction - before installing them in the chassis :
1 - checking the PA HV supply.
2 - checking the Preamp and Bias supplies.
3 - checking the LEDs, Fan, fuse blown indicators.
4 - general test without tubes using a Variac.
5 - general test with tubes using a Variac.
Access to all parts is organized for maintenance, nothing is definetly "locked". Of course, you may need to dismantle some for certain item removals, but I consider this as normal.
Since I worked on my prototype as close as possible to the finished amps, I had no bad suprises, only some few inattention mistakes while wiring !
But it's me, OK ?
A+!
:
Summary of OTL Circuits
Some of those on this thread may find this information useful. I posted it a while ago on another thread, some may have already seen it. My own preference is the Circlotron. It is completely balanced, no trick circuits to attain balance.
The file is in two parts, otherwise it is too large to fit into the DIY allowed file formats.
I did build a copy of the OTL amplifier described in the June 1954 issue of Audio magazine, it used 40 db of NFB to get balance. With three 6AS7s it drove a 16R speaker OK. But that was in 1956, I've got no test results at all.
I've never tried an OTL since. But did build a transformer loaded version of the Circlotron, with a pair of 6550s or KT88s it easily manages more than 50 watts. And doesn't heat the house up!
Some of those on this thread may find this information useful. I posted it a while ago on another thread, some may have already seen it. My own preference is the Circlotron. It is completely balanced, no trick circuits to attain balance.
The file is in two parts, otherwise it is too large to fit into the DIY allowed file formats.
I did build a copy of the OTL amplifier described in the June 1954 issue of Audio magazine, it used 40 db of NFB to get balance. With three 6AS7s it drove a 16R speaker OK. But that was in 1956, I've got no test results at all.
I've never tried an OTL since. But did build a transformer loaded version of the Circlotron, with a pair of 6550s or KT88s it easily manages more than 50 watts. And doesn't heat the house up!
I could test yesterday evening and this morning my U-OTL amps on my Klipsch Heresy I (with corrected crossover), in my small room :
The Heresy are well loaded and driven by the U-OTL, revealing their often underrated potential... Everything is fine !
Voilà, nous y sommes !
22 pages later...
End of the Ultimate OTL 6080 Saga... Thank you Guys for following it so far !
Cheers !
The Heresy are well loaded and driven by the U-OTL, revealing their often underrated potential... Everything is fine !
Voilà, nous y sommes !
22 pages later... End of the Ultimate OTL 6080 Saga... Thank you Guys for following it so far !
Cheers !
Thank you @Brice !
@jjbunn : It depends on the design, of course. Not all OTL amps are equal on that point !
I can speak about the original Futterman patent design - since I have made tests. 6080 Off-Specs will provide :
- increased distortion.
- reduced power output.
In the case of my amp, if a tube really goes bad (cut or short), the power stage supplies +115 and -115V are fused. No danger for the speaker : I made shorts and cuts tests to check it.
Update on July 2023 : same as August 2021, my U-OTL still work fine as on their 1st day.
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