Arch Nemesis - High voltage version

[oon_the_kid]

Hi,

I was just looking around at the Arch Nemesis amplifier.

I am aware of the thread of this article, however it seems that the biggest challenge is the transformer will have to be made out of a core of unobtanium and wires of expensium. 😉Normal transformers for SETs would not do due to the wrong DC current ratings and turnings.

I wonder if anybody has ever sucessfully built a high voltage, low current version based on normal SET transformers?

My guess is the semisouth part other than having gone in the way of the DoDo is also less suited for low current performance. The current of a few tens of mA would put Vgs pretty much at Vt, which is not where it would like to be.

I was wondering if there is anybody out there who has sucessfully implemented a high voltage low current Nemesis like circuit using a normal SET transformer...

Oon

 

[jan.didden]

I'm not aware of it, but it's an interesting idea, worth pursuing.

jan

 

[flg]

Possibly the R550 would be more suited to your idea? Or maybe some of those expensive RF devices. 😀

 

[kasey197]

This may have some useful information :
http://www.diyaudio.com/forums/pass-labs/192450-sic-puppy-se-amp-using-semisouth-085-jfet.html

 

[oon_the_kid]

Hey Kasey,

Looks interesting. Too bad the semisouth has gone the way of the Dodo, even if you can get the circuit to work decently, still have to substitute the transistor.

I was thinking of something hare brained... putting about 40 of these in parallel.

http://sg.element14.com/diodes-inc/ztx658/transistor-npn-e-line/dp/259718

Back to transistors...

But it is still castle in the air. But it is good to know somebody got the semisouth to work...

Oon

 

[flg]

That sure is a funcky part??? 😕

 

[flg]

Try to find some of the HF SiTs. I searched but ??? I know I've seen some that look good but don't have the current capability of an output part. Can't remember where I saw these things. Maybe the Sic threads??? The ZV9/F3 threads??? There are some nice parts for RF that you might be interested in but I can't find 'em myself now

 

[vdi_nenna]

flg, search for threads by member "vladimirk". I think I saw a SIT amp schem based on SIT used for radar. Hope I didn't dream that, but I think that's what it was based on.

 

[vdi_nenna]

http://www.diyaudio.com/forums/pass-labs/220963-sit-amp-idea.html

 

[oon_the_kid]

I was thinking off the old type of circuit. Something like this. Look under transformer coupled.

http://www.electronics-tutorials.ws/amplifier/amp_5.html

I was thinking of using 50 pcs of the transistor to replace the main transistor. The resistor at the emitter will be about 1k. The will have 1mA through each of them running a power supply of about 300V.

It will only be single stage.

Any thoughts on that...?


Oon

 

[Nelson Pass]

I have spent some time with this, and I can tell you about a couple of
issues. The SITs that I've been able to play with required a seriously
negative Vgs in order to bias the part at the relatively low currents and high
Vds voltages, in many cases near the Gate-Source diode breakdown voltage
of the part.

On top of that, the Gate leakage current gets higher at these Vgs figures.

In the end, SITs are a good emulation of triodes at the lower voltages and
higher currents needed by speakers, which is nice. If you really want to use
SET transformers, you are really probably better off with tubes.

😎

 

[oon_the_kid]

Hi Nelson,

Thanks for the inputs. I wasn't really thinking of the SITs. Last I checked it was made of unobtanium unless one is a relative of a certain Nelson Pass. I was looking at more of the bipolar transistor, particularly the ztx series.

The other issue I was thinking about is the additional voltage generated by the transformer coil and if could damage the transistor. So do you think it would be wise to put a diode across the transformer?

Oon