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The Stax Thread III - Page 235

post #3511 of 11926

God just beautiful !

I pm you ;)

post #3512 of 11926
maybe you'd be interested in the gm70 tube- I've heard it's a cheap Russian 845? I noticed you ditched the first chassis, I was a real fan of the copper.
post #3513 of 11926
Quote:
Originally Posted by NoPants View Post

maybe you'd be interested in the gm70 tube- I've heard it's a cheap Russian 845? I noticed you ditched the first chassis, I was a real fan of the copper.

 



I'm a great fan of the GM70, particularly the copper plate version. I've used it extensively in speaker amps and once used it in a headphone amp designed for the K1000. I would have used it here except for it's tremendous filament requirements (20V@3A). The larger filament power supply would have required a third chassis. On the other hand, it's pretty hard to go wrong with an 845. It's one of the most linear high level voltage amplifying devices of ever built. I'm using metal plate versions that were briefly built a couple of years ago. They sound excellent but they were subject to failure at full 845 power ratings. Running them here at 700V@60mA, which is about half rated power. Never heard NOS, which is probably just as well considering their stratospheric costs.

I like copper chassis work too. It's just gotten too expensive. Years ago I bought a stock of .125" copper plate at below scrap prices . It's pretty much gone now. Copper plates for the two chassis of the 845 amp would have run over $400.00 plus finishing. These days I'm using powder coated aluminum. It's also a LOT easier to work than the copper.
post #3514 of 11926

It must be a little "trader" when making amp : D

post #3515 of 11926
Quote:
Originally Posted by schorsch View Post

Congratulations,
I'm still looking for a X1t and a ca-x pro

Regards Georg

PS: i can swap a CA-Y, SRA14S with extra cards or Even a SRA 12S

I had the CA-X Pro for a couple of years, great gear with very impressive shunt power supply. Its achilles heel are the air condensers which died on mine. I sold it to another Stax enthousiast who apparently got US-made military air condensers for it.

post #3516 of 11926

Frank - cosmetics question for you-  what are you using for that black edge around the  chassis top plate?

 

And- it's hard to see from the photo - but what is the chassis top plate?  Copper?  Looks kind of like copper.  It's hard to capture the color of polished metal on a photo, just like you can't convey the chatoyance of certain woods in a picture.

post #3517 of 11926

Kevin-

 

The SiC devices like amazing parts, do they have linear enough regions to use as amplifiers? 

 

 

GA08JT17-247

Drain to Source Voltage (Vdss) 1700V (1.7kV)
Current - Continuous Drain (Id) @ 25°C 8A (Tc) (90°C)

 

GA04JT17-247

Drain to Source Voltage (Vdss) 1700V (1.7kV)
Current - Continuous Drain (Id) @ 25°C 4A (Tc) (95°C)

 

They have a max dissipation around 9~15 watts, and seem to work happily up to 125 C  and higher in certain pulse uses...

 

 

The Cree SiC parts are lower in cost and some have higher dissipation, I haven't really looked at these yet to see if they will work as amplifiers.

post #3518 of 11926

they are very linear and low distortion as long as you use enough current.

which is why they need bigger heatsinks

post #3519 of 11926

Sounds like these would work well in a dht application too

post #3520 of 11926
Quote:
Originally Posted by milosz View Post
 

Frank - cosmetics question for you-  what are you using for that black edge around the  chassis top plate?

 

And- it's hard to see from the photo - but what is the chassis top plate?  Copper?  Looks kind of like copper.  It's hard to capture the color of polished metal on a photo, just like you can't convey the chatoyance of certain woods in a picture.

 

The black edge is Gabon ebony. The top plate is a two-tone textured powder coat consisting of aged copper and a sort of dark coffee color. The wood is quilted maple, which although you can't tell it from the photograph, has an almost three dimensional depth to the figure.

post #3521 of 11926
feel like posting a schematic?
post #3522 of 11926
Quote:
Originally Posted by NoPants View Post

feel like posting a schematic?

 

If someone is really interested, I'm  happy to share any information, including schematics via PM. However I'm a little hesitant  to post a public schematic of something with an 850V power supply.

 

It's really a fairly simple three stage SET amp. First stage is a CCS loaded type 76 triode that is directly connected to a 6V6. Second stage is the 6v6 driving an interstage transformer. Output is an 845 DHT driving a high level phase-splitting transformer. Only things unusual about the design is that the 845 runs on "fixed" bias (unusual in an SET amp) and that all of the power supplies, including the B+, are regulated. Eventually I'll probably try a directly-heated heated driver. The Russian 6P21S looks like an interesting candidate to replace the 6V6.

 

Appreciate your interest.

post #3523 of 11926
Quote:
Originally Posted by FrankCooter View Post
 

 

The black edge is Gabon ebony. The top plate is a two-tone textured powder coat consisting of aged copper and a sort of dark coffee color. The wood is quilted maple, which although you can't tell it from the photograph, has an almost three dimensional depth to the figure.

 

I thought that might be Gaboon ebony. But, I thought, perhaps it's some sort of plastic or oxidized metal or who knows. Nice contrast.

 

Powder coat?  Do you do your own powder coat? I've been trying to develop my own aesthetic as I build things, and powder coat was something I considered, but local shops want a ton for small jobs. Same for anodizing.  I've used bead blasting and polishing on metals, but I haven't been able to figure a way to get powder coat or anodizing done without spending a fortune.

 

[NOTE: I build amps, including amps for STAX - hence this post is vaguely Stax - related.  The more I learn about fabrication, the prettier my electrostatic amp can look.]


Edited by milosz - 11/3/14 at 3:22am
post #3524 of 11926
Quote:
Originally Posted by kevin gilmore View Post
 

they are very linear and low distortion as long as you use enough current.

which is why they need bigger heatsinks

Ah.  Thanks.

post #3525 of 11926

What are people's opinions on how the new Stax range compares to the older models? I'm very happy with my Lambda Pro Signatures but wandering how much of an improvement I would see if I invested in a modern pair.

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