Author Topic: Mars 2020 - 6V6G - 6J5 - 6SJ7 - push-pull  (Read 714 times)

Offline handsome

Re: Mars 2020 - 6V6G - 6J5 - 6SJ7 - push-pull
« Reply #15 on: August 01, 2020, 08:30:12 AM »
You don't get more power using the balanced but you do get less distortion - see my measurements at the bottom of the schematic. Will start a thread - apologies for the semi-hijacking @karel

Offline Mars

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Re: Mars 2020 - 6V6G - 6J5 - 6SJ7 - push-pull
« Reply #16 on: August 03, 2020, 12:16:01 PM »
No problem, handsome, you made some good comments to offset the hijack ;)

Here is the drawing for the enclosure - brushed stainless steel with laser etched lettering



The choke will be mounted underneath.
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Offline Mars

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Re: Mars 2020 - 6V6G - 6J5 - 6SJ7 - push-pull
« Reply #17 on: September 07, 2020, 04:11:50 PM »
Hi All

I have received the metal work





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Offline Den123

Re: Mars 2020 - 6V6G - 6J5 - 6SJ7 - push-pull
« Reply #18 on: September 07, 2020, 05:45:19 PM »
Looking good Karl. I am really battling with ma mechanical layout at the moment.

Offline fredeb

Re: Mars 2020 - 6V6G - 6J5 - 6SJ7 - push-pull
« Reply #19 on: September 07, 2020, 07:40:58 PM »
Yes , that is a stunning layout . Form follows function , and it looks good .
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline Mars

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Re: Mars 2020 - 6V6G - 6J5 - 6SJ7 - push-pull
« Reply #20 on: September 08, 2020, 10:34:33 AM »
Let us put it together, and see how practical it is :whistler:
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Offline fredeb

Re: Mars 2020 - 6V6G - 6J5 - 6SJ7 - push-pull
« Reply #21 on: September 08, 2020, 01:12:22 PM »
Let us put it together, and see how practical it is :whistler:

I'm sure it will be stunning , I like the way the driver faces the output tubes head-on .

Will the choke be bolted on below the power transformer ?
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline Ampdog

Re: Mars 2020 - 6V6G - 6J5 - 6SJ7 - push-pull
« Reply #22 on: September 09, 2020, 06:10:22 AM »
Another matter noticed is the all too frequent erroneous connection of an input pentode, when global NFB is applied. I refer to the screen bypass capacitor (0,33µF) which goes from g2 to common. The correct connection is to the cathode of the 6SJ7, when this is no longer bypassed to common. To briefly rehash, true pentode operation is only obtained with screen connected to cathode so as to make the operation a constant current one. This will be true if the cathode is bypassed to common as well - the normal operation of a pentode.

As shown, the NFB signal will now appear between cathode and screen, being some 20x the input voltage and in opposite phase to the input. Apart from rendering the pentode gain to a figure similar to triode operation, it also yields a weird transfer graph (one supposes this error is because of the habitual way a screen bypass capacitor is connected). The correct way is to take the negative end of the bypass capacitor to the valve cathode.

Correcting this in this kind of fashion may also produce oscillation with applied NFB as a result of increased loop gain, which should be watched out for and and corrected. (This error appeared even in some well-known amplifiers.]

On a happier note, some of our long term members might remember the late Abe Venter (Viagara). I had the pleasure of again meeting his erstwhile companion and only female member for a while, Fem.Audio.Connoisseur, who sends her greetings. Though living at opposite ends of the Republic, we are going to collaborate in placing some valve amplifiers on the market - not a profitable niche of the audio market, but a rewarding pastime for both of us nonetheless. 
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline fredeb

Re: Mars 2020 - 6V6G - 6J5 - 6SJ7 - push-pull
« Reply #23 on: September 09, 2020, 10:58:04 AM »
On a happier note, some of our long term members might remember the late Abe Venter (Viagara). I had the pleasure of again meeting his erstwhile companion and only female member for a while, Fem.Audio.Connoisseur, who sends her greetings. Though living at opposite ends of the Republic, we are going to collaborate in placing some valve amplifiers on the market - not a profitable niche of the audio market, but a rewarding pastime for both of us nonetheless.

Hi Ampdog , good to see you here again !  ;D

Excited to see what you and Fem.Audio.Connoisseur come up with .  :thumbs:
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts