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Old 3rd June 2012, 03:26 PM   #1
Einric is offline Einric  United States
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Default ECL82 Single Tube Amp

Digging around on the net I found a very simple schematic that is very easy to follow.

Any thoughts? Any possible issues? Any improvements?

Thanks
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Old 3rd June 2012, 05:50 PM   #2
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The 6BM8/ECL82 is nice tube for making low power amps.

IMO, the circuit shown leaves much to be desired. It uses full pentode mode and no NFB. Can you say IM distortion and a wretched damping factor?

Contact member Jeff Yourison for the particlulars of the "Dirt Cheap SE" project he and I worked on. We tweaked an old Mullard design and the result deals with the issues outlined above and more.
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Old 3rd June 2012, 06:48 PM   #3
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Three Watt Economcal Stereophonic Amplifier

You can't go much wrong with this. Just a few little tweaks and the ECL82 could be used instead of the ECL86.

Regards,

James.
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Old 3rd June 2012, 07:04 PM   #4
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Useless with such Zout due to unexisting NFB, just as ELi says.

But you could mybe go UL and cathode feedback over the secondary to make it acceptable. That way you will avoid GFB.
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Old 3rd June 2012, 07:22 PM   #5
Einric is offline Einric  United States
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Would it be relatively easy to add NFB to the above posted circuit?
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Old 3rd June 2012, 07:26 PM   #6
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Sure. A series resistor from the secondary of the output transformer to the cathode of the triode. You may need to reverse the connections to the secondary to assure that you're getting negative feedback rather than positive feedback.
It may not be the ultimate amplifier but it would be worth a try.
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Old 3rd June 2012, 08:13 PM   #7
Einric is offline Einric  United States
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It looks like I'd be into the stereo setup around $200.
The heater circuit in my aikido doesn't have enough overhead to run the heaters for this circuit also.

What do you all think about my $250 budget and could I do better?
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Old 3rd June 2012, 08:29 PM   #8
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I run EL82's push pull as a headphone amp with AC heaters - no noise - so no need for a DC supply.

Shoog
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Old 3rd June 2012, 10:29 PM   #9
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What do you all think about my $250 budget and could I do better?
Enric,

That much money is in the range of a scratch built "El Cheapo". Magnetics are always the big ticket items. So, let's start with budget O/P trafos. Edcor's $37.01 model GXPP15-6-8K will give satisfactory results into both 4 and 8 Ω speakers. You will be restricted to triode mode "finals", as the magnetic headroom necessary to employ ultralinear (UL) mode is absent. The power yield is approx. 6 WPC, which works well combined with mid 90s sensitive speakers.

IIRC, the "Aikido" preamp has some gain. That means you get to "ditch" the volume control circuitry and switch to the inexpensive 6J6 as the splitter driver.

BTW, any member of the 6V6 "clan" works with the parts values shown. "Obscure" tubes other than the 'AQ5 include the 12AB5 and 14C5.
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Old 4th June 2012, 12:38 AM   #10
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Here is Morse's SE ECL82. A thread somewhere on this. He liked it. You'd need complementaty speakers as it is a current amp

dave
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