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

Most exotic SET power amplifier

Hi guys!
As I promised you a few days ago, I will post some pictures of the project I'm now finishing. It is an exotic power amplifier equipped with 211 power tube.

Due to the unique specs, I would say that I'm quite certain that this might well be one of the most exotic amplifiers ever made. There will be several posts regarding the specifications afterwards, for the time being I have uploaded some pictures of this unique project.

It is a 35 W/ch Class A2 power amplifier around 211 output tube, with 300B driver tube and EML20A input tube. There are totally 15 iron pieces spread allover, all of them in double c core configuration. Signal path is 8 cm from input socket to 1st tube grid and around 20cm of copper leads coming out of the OPT secondary, directly soldered onto the loudspeaker connectors.

For the time being enjoy the pictures.


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2007-07-12 1:42 am
Wow, it's certainly large and littered with iron. Looks a bit like a small power sub-station. :D Also interested in the chassis construction. Do you have a full set of specs, i.e., freq. response, power bandwidth, THD, signal-to-noise ratio, etc.? And what are you driving with these large amps?

Regards, KM
Totally uncalled for. :(

Please tell us what the chassis is made from. I like the smooth finish with rounded corners and the fact that I can't see any bolt heads for the tube socket mounting. But I must say that I don't see the need for so much iron on a monoblock.

Hello! Thanks for your feedback!

The chassis is made out of highly glossy corian. It is CNC machined with utmost precision at the best technician in Athens. Personally I hate bolt heads jumping out of the surface, so everything was done from the downside. There exist more than 500 bolts on each mono chassis but only two are visible, the ones that connect the IEC mains socket.

The amount of iron is the least required for this design. I have wound everything by myself so I know what I'm writing of. The extraordinary performance of this amp relies on the quality and quantity of iron pieces. There are 7 power transformers, 3 signal transformers (2x IST & 1x OPT) and 5 HV supply chokes, all in double c core configuration. All this per chassis!

Tomorrow I willupload the rest pics, with the covers fully mounted.

Regards from Greece!
Excellent work, Sir! A totally insane realization!! Love to see such creations.

I am not sure what "exotic" means but I think that weight and number of transformers factors into the equation somewhere. Also, I like the mercury bridge at the far end.

Look forward to reading more.

How does it sound?

Thanks for your feedback Sir!
This is the 1st of some amps that are going to come. As we progress, level of insanity rizes! Be patient and you will see, trust me!
Yes, the quality and quantity of transformers factors in the equation. Everything is pushed to the extreme. Total weight must be somewhere between 100 and 120 kilos, have yet to check it fully mounted.
The MV rectifiers do not make a bridge, they are 2 simple HV supplies there, one for input & driver stage and another for the output stage.
Freq response is not that extraordinary at first glance (around 30kHz) due to the relatively high impedance of the output tube but the linearity of tubes operation goes well down to subsonics. This is the key of the extraordinary performance of this amp. The signal transformers are monstrous with an enormous amount of primary turns and the freq response is practically the same as the freq response of the output stage. Power output is 35W/ch at <2% Class A2 IST driven.
This amp is going to drive Jadis Eurythmie, the OPT can be reqired for 16 Ohms operation as well.

Thanks for your kind words.
Greetings from Greece!
I kinda like the Frankenstein presentation, though, it does raise several safety concerns... Good to hear that you're planning to cover the transformers. I'm curious to see the final product.

The iron does indeed look custom wound. Bravely done.


Safety concerns? why?
Everything has already been covered but will be uploaded tomorrow.
Every iron piece has been wound manually, it is custom built.


2005-10-30 12:57 am
I don't see a 1:1 correspondence between tubes and transformers... wondering if there are solid state devices doing amplification?


I think some of those transformers are chokes, and others are to power the rectifier filaments. When you have your own transformer winding machine and can produce whatever you need on demand, you have more options.

A high power SET amp will necessarily be heavy. They are usually split into multiple units, like having the power supply in its own enclosure. I designed a yet-to-be-built GM70 amp that would weigh about the same, but is split into 3 units. Personally, I think the weight of this amp is actually reasonable for a Class A single-ended amp of this power level, be it tube or SS.

It's cool. Guests at the house always inquire about the big SET amp with bulbs that glow brightly (mercury vapor rectifiers and GM70 thoriated filaments). It's always a good opportunity to show them your favorite music played through them. Breathtaking sound. Nobody ever asked about that small, efficient 400W Hypex amp sitting in the corner. That one was an exercise in pure practicality and accurate reproduction, but it never gets used these days.
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