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Old 21st March 2013, 08:03 PM   #1
Tyimo is offline Tyimo  Hungary
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Default Wanted! 12AU7-Mosfet hybrid from Musen to Jikken

Hi!
Has somebody any info about this amplifier?

Greets:
Tyimo
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Old 21st March 2013, 09:19 PM   #2
kees52 is offline kees52  Netherlands
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this is a better one.

tested already.

Last edited by kees52; 21st March 2013 at 09:49 PM.
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Old 21st March 2013, 09:52 PM   #3
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by kees52 View Post
this is a better one.

tested already.
I did drawn a fast amp so like yours, but did dc couple the mosfets like I always did with my amp here who plays now for already 7 years.

It is afcourse simple, decoupling and such you have to do yourselfs, this can sound nice, little high distortion most second harmonics..

R4 is offset and R7 current mosfets.

Just a idea.
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Old 22nd March 2013, 08:27 AM   #4
Tyimo is offline Tyimo  Hungary
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Thanks, but I am looking for some infos about the MJ amp!
Quote:
this is a better one.
Why?
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Old 23rd March 2013, 11:54 AM   #5
Tyimo is offline Tyimo  Hungary
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Cassiel wrote it in the tube amps forum:

Quote:
No, sorry, only the schematic. Got it from the Solid State forum, maybe if you ask there....
This is why I am trying to get info here..., but still no luck....
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Old 24th March 2013, 01:41 PM   #6
Tyimo is offline Tyimo  Hungary
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It seems that nobody is interested in this topic...
One question:
Why is the complementary buffer stage connected to the + and - 120Vdc of the SRPP tube section??
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Old 24th March 2013, 05:10 PM   #7
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Built this amp some ten years ago,(the DC coupled version) worked perfectly for many years, very-very good sound from this one... One thing to pay serious attention, is the powerup sequence, if you turn it on like on the schematic, you will have huge DC swing (and possibly destruction of the FET-s) while the tube heats up. One thing you can do (what I did) is insert a relay beetween the tube output (the two ends of,R7) and the gates of the FET-s with an approx. 40-60 sec delay. Also using Zener protection diodes on the gates is a good idea. What other info you are looking for?
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Old 24th March 2013, 07:50 PM   #8
Tyimo is offline Tyimo  Hungary
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Thanks, but I need info about the MJ amp. The first one.
Why is the complementary buffer stage connected to the + and - 120Vdc of the SRPP tube section??
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Old 24th March 2013, 08:14 PM   #9
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To have positive and negative bias voltage for the output mosfets.
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Old 24th March 2013, 08:18 PM   #10
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As you see on the original (MJ) schematic, it is a voltage divider composed by the resistor chain between the + and the - 120V rails of the tube stage power supply. These elements provide the necessary Ugs bias voltages (approx +/- 1.3 Volts) for the output Fet-s. The middle point - the common leg of the two360 ohm resistors- should be at 0 volt (you can adjust it with the 5k trimpot on the neg. side). To change Io of the Fet-s, you can alter the values of the 360 ohm resistors (more resistance - higher Io). With the given values the idle current is around 0.5-0.6 A - see the diagram
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