20b is the only candidate? and you're referring to the grounded grid amplifier?

Is DC supply here be a better choice to reduce humming issue? (compromise though)

This make it easier for tube rolling.

DC supply for something like this is tricky.  The heaters are sitting at -450VDC (or -400VDC if you run it at a lower voltage). 

http://www.ebay.com/itm/SiTubes-LPF-Low-Power-Isolated-DC-Filament-Supply-/161719174157?hash=item25a736c40d:g:EBMAAOSw~OdVaIav

 

something like this might work, I remember seeing it from scavenging around millett's site

20B-v4 really is the only candidate that i know of that does both 800v and has a center tapped filament.

Even if you run DC for the heaters, and then you need 4 of those boards.

 

Edited January 8, 201610 yr by kevin gilmore

The 20B-x4 is indeed the only tube suitable for this role.  All other DHT's would require changes to the circuit to work. 

that tubes cost is a bit ridiculous though, hate to think what the cost is for the all-DHT amplifier..

the all dht version is $18k or so in parts.

you want the best thing there is, the ggdht (which i just posted) is as close as you are going to get for <$10k

here is the thing, the gain of this amp, and there are only 2 other ways to do the filament, both have problems with the high gain.

1) hum pot between the 2 filament wires, the center of the pot is the cathode. This limits the voltage gain of the output stage a bit.

2) high frequency center tapped transformer, 40khz minimum (seriously, everything else sucks) and then there is still hum, but you can't hear it.

this is the problem with using DHT's in a dc coupled electrostatic design.

Also why 300B's are absolutely the wrong thing for the job.

 

http://www.emissionlabs.com/Articles/APP-NOTES/AN6-Center-tap/center-tapped-index.htm

Edited January 8, 201610 yr by kevin gilmore

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Just an observation with the fat psu boards. The silkscreen states an input of AC360, I presume this is the loaded voltage, if so the board default would be the 450V yet the outputs are 400V on the silkscreen?

Edited January 14, 201610 yr by johnwmclean

We always specify loaded voltage.  If it rises much above that (plus line variation) then the caps would be in trouble. 

1 hour ago, spritzer said:

We always specify loaded voltage.  If it rises much above that (plus line variation) then the caps would be in trouble. 

So then the output stated on the silkscreen is wrong, it should be 450V not 400V. Or am I having a blond moment.

Yup, that should be 450V. 

John, my wife would be offended by your blond moment comment 

On 1/14/2016 at 4:15 AM, johnwmclean said:

Just an observation with the fat psu boards. The silkscreen states an input of AC360, I presume this is the loaded voltage, if so the board default would be the 450V yet the outputs are 400V on the silkscreen?

FWIW, I did a bit of testing; the drop out voltage of the GR HV PS is about 9 VDC for my build which is configured for 400 VDC output.

Nice  

I was seeing between 9V and 12V dropout.  That's awesome for an HV supply.  That sets the AC360 perfect for a 450VDC output including the possibility of a 10% brownout.

7 hours ago, eggil said:

John, my wife would be offended by your blond moment comment 

My wife was offended and she’s within plate throwing range. 

And the regulated voltage is rock steady too. In the 7 weeks or so I've been using my GR HV PS, the voltage has not varied more than 0.5 VDC from cold start to fully warmed up. Quite remarkable!

Thanks again to Kevin and Kerry for a great creation!

My friend and I are excited to join in on the fun but we sadly missed the group buy.

Are there any board sets left and failing that who would you recommend for quality board production? 

(By the way hello yup first post... I'm on head-fi)

I’ve managed to get my enclosures finalised, I’m be using existing Heatsink profile sourced from China.

I’m nearly at a stage to send off the order and have been checking the FPE files over and over for errors, I always get nervous at this stage...

I’ll be mounting the boards directly onto the heatsink, the only problem with this is the C2M1000170Ds end up being around 10mm ht with the 4180g pad and screw head, so under each C2M1000170Ds I’ll be drilling a 2.5 mm cavity for a bit more room.

I would move the transformer further away from the volume control as it is so prone to pickup noise there. 

Ohh and you need at least 12mm stand offs if you want to mount the boards directly to the sinks.  My latest ones have all the holes removed to make mounting this way easier. 

if you don't already have the boards, there are new shorter versions of the boards that make doing the c2m1000 much easier

Wot, only ONE headphone socket...?????                                                  

Talking about transformer.....

Some will prefer a much over killed ones like 500VA, while others will just meet the spec. How do you guys think?