spritzer

There has to be some ancient order of soldering monks that teach this shit as I just don't know how to do it this badly. Needless to say, that PCB went up in flames even after I tried to fix it...

This is a good example of how you should not solder a diode in a +/-500V supply.

This is about as simple as it can get but care has to be taken when soldering in the tubes. There are no cheap sockets available for sub-mini's so they have to be soldered in. I didn't care enough to make a new footprint for them so this is a TO-5 base which is quite small. Should be fine with non-Hennyo solder skills.

They are certainly the best dynamic ever made, I brought the Senn dealer here an impedance adapter this week for them to try out. They were pleased by the difference but I'll have to visit them again once they've had some more time with it.

Crap!!!! Nahhh... just kidding. The production version is a bit different.

Now something to use with the mini switcher above, a subminiature tube electrostatic amp. The pcb is less than 120*90mm for both channels and it is fully balanced from input to output. Only one B+ for both given the voltage constraints of these tubes so limited voltage swing but who cares... it will look cool.

Better yet, use a phono stage. That's really vintage!!

Sovshiller liked them so I have my doubts...

There are voltage issues at play here so stick with the 1K pot.

Just a tad...

Which version are you using, IXYS or the A1968? Personally I'd only do this on the Sanyo part... As for how much current, until there is smoke. You can also tweak the offset series resistor to give you more range.

Let's put it this way, throw water on the amp and it evaporates quickly enough to not short out the circuit...

Yes but it isn't true as you can do much better matching than the factory job and link the two dies thermally. This guys claim was more than there were still plenty of P-fets to be found in duals as he was able to get some.

I'm a bit amazed you could read that thread. The guy is a bit of a case but in a nutshell he wants a separate PSU for the low voltage section (which draws almost no power) but not for the high voltage (which draws all of the power), less feedback and bigger caps. He also calls the amps cheap in terms of build quality and shames Stax for using single transistors matched into pairs. The guy has clearly never built anything as a product or indeed lives in the real world.

Nothing springs to mind.

The heat aspect is hard to judge, way too many variables but dust inside the unit can also be a factor. It the amp is one of the first built then you can be running into cap problems given the super simple power supplies.

Hey!!! I just got home from work... 400V isn't enough for any serious amp. I have some 3900uf/550V caps here somewhere and some 3*110uf/630V film caps. Two of them are the size of that 717...

That smoked on the trainwreck board I'm repairing so it is worth a shot.

All the grounds on the Alpha PCB are connected to the ground plane so everything is shared. If you ground the inputs directly into the PSU then one wire to the pot is all you need.

Here is how far I got until the next Mouser shipment: All the transistors are the originals and there are a lot of them.

Some progress aka I'm out of parts... I did use the W transistors on this one as it's all I had. More power handling which is good in my book.

This piece from a recent Hifi-news does explain some things...

The B+ should be a bit lower so 250 for that and 270 for the B-.

All Stax Pro bias sets will handle 1200Vp-p in an ideal world but humidity is a huge factor. I read somewhere back in the day that the bias was 200V so you could be close to it. Low bias with high voltage swings on the stators is certainly one way of doing it...

Some progress: I didn't order the PSU boards as they were never 100% finalized. A Sigma22 works just as fine for testing though.