stax t8000 clone (well sorta)

[Kerry]

Excellent! 

I think the right part number for Q16, Q18 is PBHV2160Z.  That's what I'm seeing on the board as well. 

Q9 and Q10 should be the higher voltage version.

Everything else you've mentioned should be good  

[kevin gilmore]

updated the board pictures, either stn9360 or 2sa1486 (people should have bunches of them, still available)

that transistor is roughly .6 watt

5 watt resistor is designed to give about 200v

3 x 68v zener in series would be around 210, so if the tube is not warm...

Edited May 17, 2017 by kevin gilmore

[kevin gilmore]

2 hours ago, mypasswordis said:

Any chance to shave just a few more mm off the length of the tube input Carbon boards? Maybe on the left side the zener string has space to be moved and the traces adjusted a little? Then I would be able to squeeze it into this standard size ebay case, which has 300mm internal length: http://www.ebay.com/itm/122099811096 

length or width, you are asking for width.  for that box, inside is 6.3 x 11.8  so two amp boards would fit on one heatsink already. no room for anything else, would have to be a two box.  I centered everything on the board, so when you put them next to each other, the tubes align.

[mypasswordis]

Yeah, I guess I mean width.  If I mounted both on one heatsink it would get very hot so my plan would be to do it lopsided, one on each side. The tubes would look a bit funny. Even putting the two boards side by side and all the way to one side there would only be 20mm left for XLR/RCA jacks and circular connector for the umbilical at the back panel, and I am measuring roughly 23mm on my panel mount XLR jacks right now so it just barely wouldn't fit. 

[kevin gilmore]

todd added zip files to the attach list, so please look at these and see if I made any mistakes

 

kgsshvcarbontriode.zip

kgsshvtubesandwich.zip

[congo5]

looks good to me,

What is voltage of .1uf cap on servo?

[Kerry]

It only sees a few volts, but for safety sake you might try a higher value that could cover the voltage from ground to the negative rail.

Can't wait to see how this performs  

EDIT:  I'm noticing that the gaps between the ground plane and traces are very narrow (not sure if I'm seeing this right).  If so, I'd recommend about .035".

[congo5]

  Thanks,  there is no ground plane at all, not at these voltages.

the groves are where I cut the 2oz copper, all that's left are  traces

Just the cut (.020") would be enough for 80v but not 800v

don't think Kevin's board files have any planes, like the grounded grid.

 

  From looking at the schematic I thought that servo cap would normally not have more than 10-20v but

on start it could see hundreds, so used a 450v Panasonic,

thanks for confirming this!

 

  I chose this one thinking it will be more different sound wise then a tube input carbon

should have missing parts this week

Edited May 22, 2017 by congo5

[JoaMat]

The solder resist - what stuff are you? From picture it seems like everything including solder pads are covered? Do you have to remove… before solder on component side?

[congo5]

EL609 Green Insulating Varnish - Aerosol - Sprayon

it moves out of the way when soldering, or reworking. don't need to mask or remove

its available locally and works but real mask is better

alcohol removes it

I like it for prototype

usually I spray when done, after flux is removed

[joehpj]

Is there actual benefit to have both 6922 and EL34 filament regulated or only 6922 is required?

Edited May 25, 2017 by joehpj

[spritzer]

The EL34 heaters are floating at -400V so it would be pretty tricky to even do that at DC. 

[joehpj]

Yeah... So, I will do it with separated winding with LT1083 regulator. All floated.

I do it mainly because I plan to use separated ps box. Running AC with DC in a same umbilical cord seems somehow compromised for me.

[spritzer]

Floating would work but I've never had any issues with AC hum on this.  YMMV though. 

[JoaMat]

It seems that G3 is tied to the plate on kgsshvtubesandwich while G3 is tied to the cathode on BH and GG. Any particular reason?

[kevin gilmore]

I will have to look that later, but I took the tube piece from the GG design

edit: this is the same as the T2, so it is what I wanted.

Edited June 1, 2017 by kevin gilmore

[JoaMat]

Did this today.

"Twin holes" along the right side of board - forgot to mirror before drilling the board, but this is a prototype and it will probably blow up anyhow…

[Kerry]

Can't wait to see what you think of this

[spritzer]

Blowing it all up is half the fun.  One amp recently tried to kill me which is less fun but still enjoyable...   

[Hopstretch]

There's no way any current could make it all the way through you to ground, Biggie.

[JoaMat]

No blowing up - no fun.   One HV up, other HV down - so no fun there either.

[Whitigir]

1 hour ago, JoaMat said:

No blowing up - no fun.   One HV up, other HV down - so no fun there either.

 

Lol! That is the best part of DIY, finding a rotten tree in the forest

[spritzer]

9 hours ago, Hopstretch said:

There's no way any current could make it all the way through you to ground, Biggie.

I think that might be true.  I'm having some truly bizarre issues with an old Stax amp and let's just say that it put 120VAC on the chassis.  I connect a source and boom!!  I got a slight tingle but that's it.  

[kevin gilmore]

Short in the transformer to ground, seen it before

[spritzer]

Yeah, I'll do some further testing with the insulation tester tomorrow.  I have the Uni-T UT-512 and who knew Uni-T made something usable?  Their meters are just garbage but this is kinda nice.  It does complain a bit at 2500V but nothing too serious.