EF86 Push-Pull "power"-amp - diyAudio
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Old 16th February 2013, 12:05 PM   #1
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Default EF86 Push-Pull "power"-amp

I was toying with the idea to build a very low output guitar amp with tons of character and distortion at reasonable playing levels. Assuming I have a custom output transformer made, what could I expect in terms of output power?

Last edited by Mikael Abdellah; 16th February 2013 at 12:23 PM.
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Old 16th February 2013, 02:28 PM   #2
Ketje is offline Ketje  Belgium
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As long as only your ideas are that strange .
Vb=300V ,Ia=3mA ,Ia=10mA peak (AB) ,Raa=100k perhaps 1,25W sinewave.
Mona
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Old 19th February 2013, 06:10 AM   #3
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Default So maybe this would be a good point to start

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Old 19th February 2013, 06:13 AM   #4
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I have looked a bit at that schematics and also read the article related to it. It looks pretty much like what I want to do.
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Old 19th February 2013, 08:46 AM   #5
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I've done the low power thing with several different tubes; 12AU7 and 6SN7 are the classics, but for pentode sound I've found that the EF80 is the best. It can take 300 V / 10mA, and you can use it with a standard small Hammond OT. Power in the order of 1 watt, and sweet sounds. Cheap price doesn't hurt.
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Old 19th February 2013, 09:23 AM   #6
Xmtrs is offline Xmtrs  United States
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Default 6BJ6

May I suggest the following 6BJ6 low power amplifier arrangement which I have used as a modulator/output amp in the past. The 6BJ6 Pentode's are wired as (in the vernacular of the 1930's) a "Class B Super Triode" (G2 to G1, not G2 to P) and operate unbiased without the cross-over distortion usually associated with that class. This circuit will provide from 2 to 5 Watts depending on the value of B+, the drive and the appropriate Plate Transformer impedance... the 150mA Heater's are a plus as well.
6BJ6.JPG
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Old 19th February 2013, 01:47 PM   #7
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Default Hmm

I did it with 4 EF 86 and Hammond 125 C Transformer.It is some time ago but I remember not being satisfied with the results
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Old 20th February 2013, 01:48 AM   #8
Xmtrs is offline Xmtrs  United States
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4xEF86 ...but I remember not being satisfied with the results...

That's not surprising to me. EF86 class tubes have sharp-cutoff grid structures and would not reproduce the soft-crossover characteristics of a remote or semi-remote cutoff "Super Triode" Push Pull Pentode arrangement. It's the very nature of the variable-mu grid structures of the Remote Cutoff Pentode which, when arranged in the Push Pull Super Triode Class AB2 configuration, result in the absolute highest power to weight ratio obtainable while reproducing 'sweet' audio qualities.
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Old 22nd February 2013, 10:18 AM   #9
Xmtrs is offline Xmtrs  United States
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Quote:
Originally Posted by Mikael Abdellah View Post
I was toying with the idea to build a very low output guitar amp with tons of character and distortion at reasonable playing levels. Assuming I have a custom output transformer made, what could I expect in terms of output power?
In my initial reply I suggest an unbiased low power amplifier arrangement (in the vernacular of the 1930's) "Super Triode" Pentode AB or B Push-Pull Amp" (G2 to G1, not G2 to P). which operate at zero-bias.This is by no means a new idea... as evidenced by my Grandson's string-fil line-powered 12AT7/2x12BA6 PP 4W Super Triode practice amp (actually, it's been passed-down, it's now my Great-Grandson's amp) originally conjured-up by me some 30+ years ago. However, if I were designing to your specifications today, for the most bang for the buck, I would do something like that, a pair of $3 tubes and an $18 'off-the-shelf iron, safe line power and string fil's:
35DZ8.JPG
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