How about remove RK27 then use space for add 2SA1968 0.5mA (150mW) CCS option for the 2nd stage?

I'm always a fan of using up some of these 2SA1968's...

Why not lets have it all (ie. CCS and the DACT)? Makes the boards bigger but .... after all its a "Megatron" .

Edited June 29, 201214 yr by Victor Chew

Inu must be playing with spice

yes it would have to be a 2sa1968, because nothing else is stable at 500 microamps.

or a 2sa1486. The 10m90s won't work. Actually the real number is 450 microamps.

Neither of these are in current production. Could probably get away with ksa1156.

dn2540 also won't work because leakage at likely temperatures is more than 500 microamps.

and with the 12ax7 in the first stage, the gain is a bit high at 65db. so i'm playing

with a 12au7 at the moment. brings the gain down to 52db.

removing the pot probably does not help with the space needed for the current sources.

We will see...

Edited June 29, 201214 yr by kevin gilmore

it should come as no surprise that only the 2sa1968 actually performs perfectly at 450 microamps.

http://gilmore.chem.northwestern.edu/megatron.jpg

place for the 330k resistors also left there.

Has anyone began prototyping the Megatron?

I'm going to order some boards soon, one for me and one for Kevin.

all tube supersymmetry electrostatic amp with dc output servo

http://gilmore.chem....du/electra3.pdf

and the one cap one transformer cascode version

http://gilmore.chem.northwestern.edu/electra4.pdf

Edited August 27, 201214 yr by kevin gilmore

The voltage gain of the 6SN7 varies from 13 to 16. If the source provides 2V (a CD player), the second stage grid, U3 (U4), could receive 26V. With R8 of 300K, and R7 of 1K, 400V for B+ will provide an adequate bias of U3?

Just out of curiosity, is the modernized T2 with SS frontend still on the table?

I know Kerry was working on something to-this-end but I'm not sure if he got to the panelisation stage (it was on BB).

everything is on the table. in fact there is so much stuff on the table, the table is going to break.

Ain't that the truth. We rush from project to project as we keep coming up with something we like. We often loose track which is why we draw up PCB's now as we go along.

I've got some T2 boards on stand by, but am not sure if I should proceed in light of these new projects coming out. Would it be wise to wait for the SS T2 or is that a ways off into the future? just itching to start buying BOM parts:)

Any news on the Megatron? BTW, never had a chance to test the 1968's I got from EBay but the 2 I tested before my trip were around 1060V

These are the measurements of my 1968s

Edit: I've put a wrong picture (

-- o --

Rodrigo

Edited September 17, 201213 yr by PICaudio

It's me who's holding up the Megatron as I'm waiting on more PCB designs before making a bulk order. Lack of time to make those but I'm getting close.

Which BC560 is the correct one for the Megatron? I don't think there is a BOM or a schematic yet. is there?

http://www.mouser.co...key512-BC560CTA

or this one?

http://www.mouser.co...lkey863-BC560CG

Also, I assume these ones are correct:

http://www.mouser.com/Search/ProductDetail.aspx?R=KA7812ETUvirtualkey51210000virtualkey512-KA7812ETU

and

http://www.mouser.com/Search/ProductDetail.aspx?R=KA7912TUvirtualkey51210000virtualkey512-KA7912TU

Edited November 16, 201213 yr by eggil

Here is something indeed a bit different...

 

http://imgur.com/QfqFu'>

WANT! ^^^

Not a lot of sand on that one.

Highly tubular hollow-state goodness!

Megatron! I can feel the heat. Enrique will be thrilled.

 

Spritzer will you be using the rk27?

RK27 is what is imprinted on the board.

I would imagine the through-hole trace pattern would follow...

I do have one RK27 sitting here so I might use it but I just got these lovely PCB's for the Alpha pots that I'm dying to use... 

Birgir,

Are you guys at all worried about having at least one of the filaments connect so close to the pot/input? Seems like a place for noise to get in early on unless one is very careful. The power supply must be a bit of a beast as well.

That filament was always supposed to be DC powered but 12VDC operation would have been a better idea in hindsight or even running them at 25V.

 

My plan for this one is to run it off a BH power supply with it and the power transformer in a separate chassis.  The amp chassis will also have to have mains running to it as the filament windings for the CCS tubes need to be as close as possible to the tubes.  So that will be 4 transformers for this one and all in the largest Galaxy cases.  Half the size of the ESX for a far more complicated amp... should be fun....