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Megatron Electrostatic Headphone Amplifier

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On 4/3/2020 at 7:09 AM, simmconn said:

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"?

Sorry,the first stage 12au7s to drive 12ax7.

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  • 9 months later...
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Finally got around to finalize my Megatron, fitted into one chassis with GRHV.     

Did some fine tuning on my Megatron. Bring the regulated HV down to 430VDC rails and changed one resistor from 21K to 15K to supply 300VDC to the front end tubes. In my case the front end tubes draw a

I made some modifications to my Megatron. Most of them are under the hood. changed the CCS tubes filament supply transformers from 25VA Antek AN 0206 to 50VA AS 0506 (one for each channel). Now

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My apologies if this has been asked before....

As normal my first steps in a build is to get the circuit diagram and reverse engineer the gerbers to check them against each other.... looking at the circuit diagram pdf the decoupling caps have been omitted... fair enough, however

1. the circuit diagram shows a single 150K resistor from the led D3 to ground but the reverse engineer of the gerbers has two 150K resistors in series to ground....

2. the gerbers seem to have two 330K resistors, one each from the 300V line to anodes 1 and 2 of the 21ax7. These resistors are not on the circuit diagram...

here is my reverse engineer with components in pink missing from the pdf:


NOTE this circuit diagram has not been checked

Edited by jamesmking
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  • 3 weeks later...

Yesterday, after three years of regular use (from 2018 to now) I measured some voltages for check how my Megatron aged.

It is very nice to see that the voltages are still similar to that I did as a reference once finished it. The EL34´s glass have gotten a bit darker with use but otherwise my "baby" is perfect.

As an anecdotal detail, my preferred valve for the first stage is still E180CC.


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6 hours ago, jose said:

As an anecdotal detail, my preferred valve for the first stage is still E180CC.


That's what I am using in my Megatron as well, Philips E180CC SQ.

Very happy with the outcome. 

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