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Old 21st July 2006, 01:17 PM   #1
simonov is offline simonov  Bulgaria
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Default 6V6GT SE schematic -need!!!

Hi all. I have some new matched 6V6GT's and some verry nice Marconi 6SJ7. I need a simple and easy to build SE schematic. I'v found this schematic :
http://www.bonavolta.ch/hobby/en/audio/6v6_5.htm
but this cathode follower doesn't look very nice to me.
Besides, I was advised not to use it

If anyone could be of assistance???

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Old 21st July 2006, 01:45 PM   #2
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Hi,

6SJ7 and 6V6 SE, eh?

Have a look at my site, you will find the most extensive and best documented circuit walkthrough available for exactly this tube combo on the whole `net, I guess. When printed out, about 25 pages on the circuit design alone

Click here for the start.

Tom
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Old 22nd July 2006, 08:46 AM   #3
simonov is offline simonov  Bulgaria
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Hi Tom,
the negative feedback is one of the reasons to choose not to use the schematic in my first post. I believe the NBF is not a benefit when we're talking about tube SE .
Did you try the schematic without NFB? How does it sound?

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Old 22nd July 2006, 01:26 PM   #4
Giaime is offline Giaime  Italy
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One can't have the knowledge to judge the use of nfb without having the knowledge to design a simple 6V6 single ended amp...
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Old 22nd July 2006, 02:01 PM   #5
simonov is offline simonov  Bulgaria
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I may have no kwolege to design mw own amp, but I have ears to hear the difference

Rgards
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Old 22nd July 2006, 02:46 PM   #6
rdf is offline rdf  Canada
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Not to threadjack but how could the Bonavolta circuit possibly work as a generic circuit? The 6V6's bias is set by the DC resistance of the output transformer and would vary widly between models. Could this circuit have been intended for a specific transformer?
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Old 22nd July 2006, 04:21 PM   #7
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Quote:
Originally posted by rdf
Not to threadjack but how could the Bonavolta circuit possibly work as a generic circuit? The 6V6's bias is set by the DC resistance of the output transformer and would vary widly between models. Could this circuit have been intended for a specific transformer?

The point about varying bias is well made. Also, notice that the 6V6 is operating in triode, not pentode, mode. A triode wired 6V6 is VERY linear.

The general thrust of that 1949 circuit is valid. The 6SJ7 provides all necessary voltage gain and the 6V6 cathode follower is easy for the 6SJ7 to drive. IMO, it could be tweaked into a CAPABLE performer. Make the PSU bipolar, as that will take care of the voltage swing at the 6V6's grid. Insert a pot. between the O/P trafo and B-. Do not directly ground the O/P trafo. Adjust the pot. to set the 6V6 Ib at 35 mA. There is a flaw in the voltage gain block. The 500 nF. cap. should connect the 6SJ7's screen grid to the cathode, not ground. The ground connection would be valid if the cathode resistor was bypassed. However, yet more linear performance could be obtained by regulating the 6SJ7's screen supply. Either a VR75 or a string of low noise Zener diodes seems reasonable.
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Old 22nd July 2006, 05:51 PM   #8
corbato is offline corbato  India
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Full time thread-jaking now.
On the '49 design, how can it be superior? More linear? Better damping?
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Old 22nd July 2006, 06:04 PM   #9
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Hi Simonov,

Quote:
Did you try the schematic without NFB?
No, because it wouldn´t make any sense at all. After all, one major point of that walkthrough was to design a pentode/pentode SE amp with gNFB.

Citing myself:

"It is a 4,5 Watt/channel pentode/pentode single ended amp which gives a damn on all this "single ended triode without any negative feedback" madness.

Instead, it is a no-fuss, well-engineered and solid circuit amp."

Tom
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Old 22nd July 2006, 08:51 PM   #10
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I've build the Bates-amplifier with the Hammond 124BSE (R = 240 Ohm), the sreen grid of the 6V6 on 180 Volt.

Best regards
Andreas
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