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Old 19th September 2004, 11:23 AM   #1
hacknet is offline hacknet  Singapore
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Default EL84 Push Pull amp.

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this is terribly interesting. i stumbled upon this schematics and i`m wondering if there is any downside to this topology since it looks super cheap and simple to build. is there anything that i would have to look out for?
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Old 19th September 2004, 12:10 PM   #2
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This one has beens discussed before.. it has every high THD.. the output stage amplifies it's own distortion, it doesn't cancel..
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Old 19th September 2004, 12:20 PM   #3
mcs is offline mcs  Denmark
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I think the only purpose of that circuit is to keep the parts count down. Why not choose something a bit better?

Best regards,

Mikkel C. Simonsen
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Old 19th September 2004, 02:05 PM   #4
hacknet is offline hacknet  Singapore
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i`m trying to build something super simple that i can tweak easily. would adding NFB help?

what would be a good start? i`m actually thinking of using 6080s in place of the el84 with a much smaller Z opt.

i`m trying to use uncommercialized output valves to keep cost down while still using NOS tubes. any recommendations?
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Old 22nd September 2004, 03:48 PM   #5
mr2a3 is offline mr2a3  Italy
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Quote:
This one has beens discussed before.. it has every high THD.. the output stage amplifies it's own distortion, it doesn't cancel..
Interesting!
I tried a seach on the forum but without success.
Please may you give me some reference for a better search (maybe keyword to use)?

Thanks!
Massimo
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Old 22nd September 2004, 05:05 PM   #6
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you got to build it with a constant current source at the tail of the differential long-tailed pair for optimum results. then it'll sound really wonderful.

if it doesn't work, or sounds as bad as some put it, then the guys on this page must be crazy.
\\http://www.diyparadise.com/ultracompact.html

donjuan
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Old 22nd September 2004, 05:42 PM   #7
mr2a3 is offline mr2a3  Italy
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Yes I agree,
I think to give this project a chance, also because I've in my junk box everything necessary (at least for one channel).

But I'm puzzled by the sentence "the output stage amplify its own distortion" (from tschrama).
I really don't understand how it may happen, but he refer to a previous thead so probably embedded in the forum there is the explanation I need . . .

Ciao!
Massimo
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Old 22nd September 2004, 10:23 PM   #8
EC8010 is offline EC8010  United Kingdom
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Hacknet, although you might not believe me at first, the price of individual valves isn't the critical thing in keeping costs down. The best way of keeping costs down is to keep the HT voltage at 300V. However, you can save significant money by going for valves that don't have 6.3V heaters. The circuit you presented (and its variations) will only work in pure Class A, so you will probably only get 6W out of it. 829B is a useful valve, and they're cheap as chips.
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Old 23rd September 2004, 06:53 AM   #9
hacknet is offline hacknet  Singapore
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haha... the 829B is cute looks like micky mouse..

anyway, i`m looking for twin power triodes. i`m considering things like the 6bx7. i will keep the 829B inview, any other tubes to recommend?
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