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Old 31st August 2008, 02:10 PM   #81
Salas is offline Salas  Greece
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Default Comprehensive Schematic.

Hello,

Some people emailed me asking for a comprehensive schematic of how I made it, with final PSU etc. So here it is. Although it is explained in the thread, its better to be in one picture.

Click the image to open in full size.

The above circuit IS NOT for commercial use. Its free to be copied for personal DIY use. Any other use needs my permission.

The Mosfet Maida style regulator used can be seen here. I made it point to point on perfboard though. You must calculate its resistor divider voltage setter for 340-350VDC. Details on how, are in the given link.

*The 15R became 20R 2W after new tubes got run in and draw less for 6V+ heater voltage.
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Old 31st August 2008, 04:15 PM   #82
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I saved a copy of this schematic. If I determine that my current 6EM7/crossover project needs more power I can rewire as a preamp similar to this and build a bigger power amp. The 6EM7 has a pretty low rp so it should do nicely in this type of layout me thinks.
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Old 31st August 2008, 04:52 PM   #83
Salas is offline Salas  Greece
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It will need recalculation for DC PSU, operating point, resistors & heater current source amperage, for 6EM7 2nd section. You can keep the main idea, but as is, the circuit values are not applicable.
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Old 1st September 2008, 12:16 AM   #84
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Yes, I should have mentioned that only the basic topology could be used since it is not only a different tube but an entirely different class (triode).
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Old 1st September 2008, 12:48 AM   #85
Salas is offline Salas  Greece
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The cool thing with the 6V6 when triode wired as in this preamp, is that it approaches DHT linearity.
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Old 1st September 2008, 04:30 AM   #86
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Appologies for going "slightly" OT.

Has anyone had experience with the circuit shown by foboleyns above. This is a triode mode variation.

Using the screen as an "anode" and AC grounding the real anode is something I've seen done with 6AU6 but not with higher power pentodes.
The theory is that the AC Grounded Anode completely surrounds the other tube elements and so should give some improved noise performance.
Can we expect any other improvements, that is, in linearity etc.

Thanks,
Ian
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Old 1st September 2008, 08:58 AM   #87
Salas is offline Salas  Greece
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Hi Ian,

I have in mind to do that experiment on first opportunity, as I have seen it in some underground Japanese, but the thing that puts me off a bit, is that we create a much wimpier tube in that way. I want strong current in this preamp for example. Plus we should expect a different set of load lines.

I will repeat Ian's question then. Has anybody reviewed that topology?
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Old 1st September 2008, 12:25 PM   #88
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Quote:
Originally posted by foboleyns
yes,The plate is run at a very low voltage, almost turning it off in this case,it make the 6V6 look like be close to a triode with low internal resistance.

A=5.5V is necessary,we can use a regulate circuit to make it adjustable for the output gain.
Interesting circuit. How much is gain, output impedance and harmonic distortion?
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Old 2nd September 2008, 02:45 AM   #89
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Quote:
Originally posted by salas
I want strong current in this preamp for example.
Why? I wonder what you are driving with this preamp, since with that 0.68 uF output cap, it must be high impedance.
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Old 2nd September 2008, 05:01 AM   #90
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Exactly so.  Even with a 100K circuit as the load, I found a 1µF output coupling cap to open up the bottom and stage beyond what I would have thought.  With a fractional µF cap on the output, we ain't gonna be delivering any big current to anything, no matter what.

On my commercial circuit, I use 2.2µF, simply because it will deliver true bottom into a 20K, or maybe even a little heavier load.

For stuff like current delivery and component values, we got to look at this stuff reasonably.


Aloha,

Poinz
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