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Megatron Electrostatic Headphone Amplifier


kevin gilmore
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  • 11 months later...

 

On 12/31/2019 at 8:21 PM, gepardcv said:

@Blueman2: You know you owe it to yourself to build one!! ?

 

On 12/31/2019 at 9:22 PM, mwl168 said:

^ that.

I think I may have a spare board laying around somewhere...?

 

1 hour ago, jose said:

You need a Megatron ... and you know it.

 

 Now you guys are just getting nasty. 

?

Aren't you the same 3 guys who made me build the Carbon, and then the Blue Hawaii BJT after that?  Come to think of it, more than 1 of you got me to build my original SRX-Plus too.    

Your taunts will no longer work on me.  ?

 

Edited by Blueman2
  • Haha 2
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Well my blue hawaii is working fine with golden ref lv and hv boards....

I want someone to convince me to build a mini t2 seems the next logical step for me without going into rare and expensive transistors....

if only i had the amp boards... or if someone would let me have the gerbers.....

<a few momments later......>

Me and my big mouth.... I tried to resist but looks like I might be building a mini T2 thanks to JoaMat....

 

Edited by jamesmking
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I am also back using E180CC (Philips SQ) now for the gain tubes. Tried a pair of 6414 tubes following the Genalex 12AT7 (labelled A2900). I have yet to try the Telefunken ECC801S, Mullard CV4024 and 7316. 

So far I liked the Genalex A2900 and Siemens ECC801S best overall for the gain tubes.

I also heard an improvement when I replaced the Tele 12AX7 with Brimar CV4004 for the driver tubes but the difference is not nearly as significant as changing the gain tubes. It may also be due to the fact that the Tele 12AX7 I was using are used tubes with unknown mileage. 

Just my 2 cents worth and should be taken with a large grain of salt - I was merely experimenting and most of the tubes used were NOS with only a few hours running.

 

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I have been focusing on gain tubes.

I've been alternating the E80CC, E180CC, 6189 ... and I think the E180CC (Mullard/Philips) is the one with the best balance (quality vs. gain level).  I liked the E80CC a lot but the gain increase was minimal compared to 12AU7. 

For the driver's tubes, I've been using ECC803S and several "esoteric" 12AX7 for a while, but I opted for the modest ECC83 Svetlana "Winged C" and a pair of Mullard CV4004 with unknown mileage too. IMO the most critical here are the gain tubes so I have not wasted much time here.

As for the "Jiml/Gilmore" modification to raise the current to the plate of the driver tube, I think it was a good upgrade (thanks to both of you and Mwl for sharing it).

If I'm not wrong, only Michael and I did the mod?

 

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  • 1 month later...
  • 1 month later...

 

On 2/28/2020 at 4:47 AM, simmconn said:

I was wondering... why the first and second stages are designed at such low operating points. 12AU7 is at 1.2mA and 12AX7 at 0.5mA. Wouldn't higher operating points give better distortion and lower output impedance and hence better frequency response at the higher end?

Probably because it's an electrostatic amplifier, the first stage needs provide 24db gain to drive pair 12au7s ,otherwise unable to reach amplititude.

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12 hours ago, hyperma said:

 

Probably because it's an electrostatic amplifier, the first stage needs provide 24db gain to drive pair 12au7s ,otherwise unable to reach amplititude.

I'm not sure if I understand your reply. In the Megatron the first stage uses 12AU7, and the second stage uses 12AX7. What do you mean by "provide 24db gain to drive pair 12au7s"?

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