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Megatron Electrostatic Headphone Amplifier


kevin gilmore
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  • 2 weeks later...

Split all Megatron posts into its own thread since Stax Mafia have got this baby on a roll :peter:

 

Kevin you can update the first post of this thread with whatever you want.

 

"Now For Something different" thread still open for any other amp development discussion.

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  • 2 weeks later...

Fuck yeah!! Dissimilar EL34's FTW. :)

I've been distracted by other projects so this one is on hold for now. What can I say, I have a problem taking on new projects such as doing the WES/Electra class amp properly with full bandwith and so it can accept SE inputs. Then there is the single ended Stax amp... 300B's!!! :D

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well there is the single ended version with 300B, (2 per stereo amplifier)

 

and then there is the push pull version. (4 per amplifier)

just in case you have any money left over after you build the first one.

Well, a three stages SET 300B with 1:2 OPTs is the amp I use with my MK1 and is simply amazing.

Sent from my GT-I9300 using Tapatalk 2

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Suddenly the four EL34 - left channel lit up like 100 % approach light at Chicago O'Hare rwy 14R and then dimmed of to zero. PSU fuse an one EL34 blown. Next set EL34s (sorry T2) in place and more dissimilar EL34s.

 

Sounds like for some reason the HV shorted to the filament.  That's the only thing I've ever seen make a tube go into headlight mode.  Could have been a flaky tube but make sure that you don't have anything actually shorting out near that tube.  It'd be a bummer to start blowing through EL34s, even cheap ones.  Nice looking build though. 

 

All the posts here and in the main DIY thread have kicked me in the pants enough to start working on my lowly KGSS again...

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If all the tubes flashed they would all be bad.  The light from one filament, running at a significantly higher voltage than it wants, was probably enough to make it look like they were all lighting up.  I once wired a transformer wrong and put the full HV winding on a tube (woops) so I've actually seen what it sounds like you experienced. 

 

My experience with tubes is still pretty limited despite having built several projects using many different kinds but in all that time I've never had a tube misbehave like you described.  I suppose that it's possible, but if these are new, barely used tubes it seems somewhat unlikely. 

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Where did the EL34 break? This can point to what really went down. Still, a burst of air into a tube running this hot will make it into a very nice lightbulb...

well there is the single ended version with 300B, (2 per stereo amplifier)

 

and then there is the push pull version. (4 per amplifier)

just in case you have any money left over after you build the first one.

Ehhh a quad of 300B's is too rich for my blood. If this one goes well then I might try something like triode strapped pentodes at higher voltage. 7403's would be very interesting due to the high voltage and dissipation properties...

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