Megatron Electrostatic Headphone Amplifier

[sorenb]

1 minute ago, JoaMat said:

Emission Labs 20B and 300B, is that the 4 pins socket or the octal socket with center tap filament?

20B octals
300b UX4

I got inspired from your Octal/UX4 pattern ;o)

[JoaMat]

Great work - more Sort Guld.

[Faust]

-resolved-

[Justaguy]

I'm looking at the 300V power supply for the Megatron XL (megatronpowersupply300v2xl in the drive) and it looks like pin 5 on the pcb has an unlabeled component connected to the +300V line. Looking at the schematic (megatronps300.pdf and megatronschem2.pdf in the drive) have a 22 ohm R27 connecting pin 5 to ground.

I'm very much a novice, but I don't think connecting a heater pin to the output line is right.

[jamesmking]

41 minutes ago, Justaguy said:

I'm looking at the 300V power supply for the Megatron XL (megatronpowersupply300v2xl in the drive) and it looks like pin 5 on the pcb has an unlabeled component connected to the +300V line. Looking at the schematic (megatronps300.pdf and megatronschem2.pdf in the drive) have a 22 ohm R27 connecting pin 5 to ground.

I'm very much a novice, but I don't think connecting a heater pin to the output line is right.

22ohm to ground on the heater/filament looks like its there to stop the heater floating and might reduce hum and is therefore probably optional. It looks like this resistor is not present in the megatronpowersupply300v2xl gerbers. It also looks like there is a 221 ohm resistor between the anode and G2 of the el84 in the gerbers which is not present in the megatronps300.pdf.  I am afraid I did not build this power supply so I can't comment on which is the more up to date or preferred version. But in general its the Gerbers which people get pcbs made from and therefore is assumed to be correctly functioning unless the threads on headcase say otherwise.

[Justaguy]

On 3/24/2023 at 12:53 PM, kevin gilmore said:

Power supply #3   tube rectified lc filtered 4 x 6l6gc fully regulated voltages. 300 volt tube rectified and 6bq5 regulated power supply. solid state regulated bias

Referring to my last post, I saw the images of the Felista audio repair and that region of the board is unpopulated.

So another question:
Is there a board for Power supply #3? (reference quote above)
megatronpowersupplyxl has the gz34 tubes and the LC filter, but no 6l6gc tubes. The 300V supply has a el84, which is the 6bq5 quoted. This theoretical full tube build would be 3 on the 300V PSU,  6(?) on the 400V supply and 12 on the amp? That would certainly be something to look at.

[Shawn]

On 3/24/2023 at 10:53 AM, kevin gilmore said:

so i posted this elsewhere because people really want to spend large amounts of money on an electrostatic amplifier that uses a pile of 300b.

this is the first of two.

Megatron xl  with 4 x 300b

Megatron xxl with 8 x 300b

Power supply #1   goldenreferencehv all solid state

Power supply #2   tube rectified lc filtered no regulation solid state regulated bias.

Power supply #3   tube rectified lc filtered 4 x 6l6gc fully regulated voltages. 300 volt tube rectified and 6bq5 regulated power supply. solid state regulated bias

high voltage rectifier tubes are gz34 (5ar4)  300v rectifier tube is ez81

 

I figure a megatronxxl with power supply #3 should come in at a retail built price of $40k

evidently one or more companies are making dc supplies that slam 7 amps into cold 300b resulting in tubes that don't last very long. so this will have a slow start quad 5v power supply board. the xxl will have 2 of these boards.

amp chassis will be about 14 x 14 x 4 inches. power supply box should be the same size.

 

the spice simulations indicate that minimum distortion is set at about 33ma, so this is likely to eat about 300 watts total power consumption.  distortion will end up about .01% at full voltage swing.

 

Based on the megatronxl layout, the second 100k resistor on the top left is float, any reasons for that?

And what is the purpose of those 10K trimmers? I assume they are for grid bias.

[kevin gilmore]

going to look at it in a few minutes. should be ground i think.

 

nope, thats the feedback on the output.  and the gerber file is correct.

not sure where you got that picture, probably here, and likely not done.

3 of the other versions had the same error, all are updated on the google shares.

no idea how that happened.

 

someone needs to go thru all 9 versions (or more) to see if there are any more errors.

i'm kind of busy waxing my brand new 2025 corvette Z06 3lz htc.

Edited 22 hours ago by kevin gilmore

[Shawn]

9 hours ago, kevin gilmore said:

going to look at it in a few minutes. should be ground i think.

 

nope, thats the feedback on the output.  and the gerber file is correct.

not sure where you got that picture, probably here, and likely not done.

3 of the other versions had the same error, all are updated on the google shares.

no idea how that happened.

 

someone needs to go thru all 9 versions (or more) to see if there are any more errors.

i'm kind of busy waxing my brand new 2025 corvette Z06 3lz htc.

The picture is from your earlier post. I will go through other files to check for any errors this weekend.

Congrats for your new driving toy. I remember the Z06 comes with a flat-crank engine which sounds insane. Does it have bucket seats?😍

[robm321]

13 hours ago, kevin gilmore said:

i'm kind of busy waxing my brand new 2025 corvette Z06 3lz htc.

💪 Congrats!