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It is currently 05 Jul 2020, 01:11

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PostPosted: 01 Jul 2020, 05:38 
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Joined: 26 Nov 2019, 02:09
Posts: 9
Location: The Netherlands
Hello all,

I have just finished and tested the electronic part of a guitar amplifier. All that is left to be done, is making and installing the bottom plate (MDF with an aluminum cover on the amplifier side as a screen).

Because the figures for a pair of EL86's in push-pull are a little bit better than those for a pair of EL84's in push-pull, I wanted to build an amplifier using EL86's for some time now.

One of the design problems was to keep the needed 200 V supply voltage for the screen grids of the EL86's constant (enough) while the anode supply voltage has to be 250 V. The screen current varies from 4 mA (no signal) to 26 mA (full power). Dropping the 250 V to 200 V with a resistor would cause to much voltage sag. But by using two ZZ1040 voltage stabiliser tubes i solved this problem.

The amplifier works very well. No noise at all with the volume turned down and very loud when turned up. And the ZZ1040's give off a lovely bright-purple glow which diminishes a bit when you give the guitar a good 'hit'.

More here: http://otl800.blogspot.com/2020/06/gitaarversterker-met-ef86-e92cc-2-x_28.html

Greetings,
Robert


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Greetings,
Robert

http://otl800.blogspot.com/


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PostPosted: 01 Jul 2020, 11:27 
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Joined: 03 Jun 2020, 11:06
Posts: 28
Location: France
Hi Robert @EL504,

Fine job here... 8-)

I went on your web page but unfortunately, I do not read Dutch... :blush:

You are probably in the 10WRMS clean tone (onset of clipping) power range with your pair of EL86/6CW5 and circuit, do you ?

Congratulations ! ;)

-tbln

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PostPosted: 01 Jul 2020, 13:35 
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Joined: 26 Nov 2019, 02:09
Posts: 9
Location: The Netherlands
Thanks, Tubelectron.

According to the datasheet of the EL86 ( https://frank.pocnet.net/sheets/030/e/EL86.pdf ) the output power for a pair in push-pull is 18.5 Watt at 4.5 % distortion (measured using a single frequency sinus input voltage). Some of that power will be lost in the output transformer, but i am using an oversized output transformer (30 Watt) that is intended for Hi-Fi so losses will be low. The screengrid supply voltage is kept constant by the voltage stabiliser tubes, independent of current draw. The anode supply voltage only varies about 2 V between no signal and full power. So i think 15 Watt is a realistic estimate.

I have used the EL86 many times. But this is the first time i have used it in something else than otl amplifiers.

Greetings,
Robert

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Robert

http://otl800.blogspot.com/


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PostPosted: 01 Jul 2020, 19:29 
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Joined: 06 Apr 2009, 10:08
Posts: 1665
Location: US Pacific Northwest
So based on the regulated screen supply and the ample B+ filter, I'm assuming that you wanted a "zero sag" type of amp. Is there a specific reason that you chose cathode bias on the power stage? I would have thought fixed bias would be more appropriate here so the A to AB transition rectification doesn't happen. Or are you looking for that higher order harmonic fullness?

Looks like a good amp for classic rock where these more fingering and less fuzz. How does it sound?

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PostPosted: 02 Jul 2020, 01:47 
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Joined: 26 Nov 2019, 02:09
Posts: 9
Location: The Netherlands
Hello Matt,

I aimed for maximum power. I have a (irrational?) dislike of fixed bias so I have never used it in my projects (I do use dc-coupling every now and than though). I just followed the Philips datasheet on the EL86. I have made sure that the two EL86's are matched.

The design is based on the clean channel of the Vox AC15. I have already made a similar amplifier (EF86 + 2 x ECL86 pp). Now I can play stereo (through a stereo multi effect).

I allways find it hard to put into words how something sounds. It fits my playing style and preferred sound. I like to listen to many kinds of music but when playing I tend to like a clean sound more than an overdriven sound. It is currently hooked up to 2 x Jensen C12Q-8 speakers (paralleled). I did not play on it at maximum power and for longer periodes because it is still downstairs (tile floor, no dampening materials there). When the casing is done, it will move to our attic where I can play more freely.

I took a look at your site. Lots of goodies there!

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Robert

http://otl800.blogspot.com/


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