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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

My Dynaco ST-70 with Bud Purvine designed transformers built by Kolarkar Audio

Hi all ,

Last few days I have been playing music through my revamped ST-70 and must say that I am very happy.
The biggest change is new OPTs that are designed by Bud Purvine of Onetics. Bud Sir has shared this with Asnain of Kolarkar audio research and he has built the new OPTs as per those designs. He also built new power transformer and a choke, both of substantially higher capacity than the originals. The power transformer has a 250V primary with a240V tap, this enables matching the supply voltage that is 240V nominal but climbs above that many a times.
The OPTs are a tad larger than the originals so we had to drill new holes in the chassis but the cover fits without any problem.
The old phenolic PCB was replaced with a new one that is based on the original schematic.
The GZ34 rectifier was treated with the "yellow sheet mod" to make life a bit easy for it. The selenium rectifier was also replaced with a silicon one.
I don't have a quad ofEL34 right now so I am running a quad of Sovtek 5881 that are sounding great.
Really enjoying this amp. Thank you Bud Sir and Asnain 🙂

Best Regards,

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Thank you Bud Sir,

Even though the new driver board has identical schematic to the original , the performance as judged by my ears is much superior than the original. My late evening listening sessions are stretching to 2 AM. Asnain tells me that he is whipping up a few more of your designs like MC step up etc and I am eagerly awaiting those.

Best Regards,

Anwesh
 
It has been an enriching and rewarding journey for us, learning from Bud Purvine Sir and putting in practice and experiencing the sonic outcomes in actual amplifier builds.

Sharing a few pictures of the builds:

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First three are F2a SE, fourth is 300B SET with a 5kg output iron, 6BG6 SE and the RS1003 SE. All the iron were hand wound by Kolarkar Audio under his guidance and tested on the respective amplifier builds. Same goes with power and chokes.

The sonic experience is hard to put in mere words. I never experienced a need for sub, playing all these even on my 2 way bookshelf speakers.

Soundstage is unlimited and imaging is spot on. Over all, a very engaging experience with natural and relaxed presentation.

More builds planned, including IT coupled EL84 PP and 300B PP, no feedback.

Samir.