kevin gilmore

Megatron Electrostatic Headphone Amplifier

737 posts in this topic

Yes, I was referring to the output tube filament terminals.

 

Tks for the reply Spritzer.:)

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How is output offset/balance adjusted on the Megatron?

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Its pretty much self balancing unless the tubes are way off.

initial testing on various tubes, the output voltage is +/-5V

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Thanks.

What determines the offset - output stage tube itself or the combination of output stage and CCS tubes?

Edited by JoaMat

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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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Most excellent Deepak! :)

Should be something new coming to the 'different thread as I'm looking into improving the WES design. By improving I naturally mean throwing most of it away... :D

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/

 

Edited by JoaMat
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My latest DIY electrostatic amplifier. It is built entirely on information in this and “Now for something different...” topics.

 

 

attachicon.gifIMG_1325.JPG

Looks very hot and nice, give us some night shots, please :)

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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.

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Edited by JoaMat

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Very Nice build Jomat. Hope the problem will be sorted out soon and you can give us an impression of the sound.

Any pictures of the PSU?

Did you etch the boards yourself?

Edited by Victor Chew

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It may be hard to compare to the T2 unless you get more tubes  ;D

Nevertheless, it will be interesting to hear your comparison.

Congratulations!

Edited by eggil

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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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Edited by JoaMat

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you do have a seperate filament transformer winding for every top tube

right??

if not, arcy sparky.

and if those windings are not rated for 500V+ then also arcy sparky.

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Edited by JoaMat

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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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