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Old 12th September 2005, 05:05 PM   #1
Giaime is offline Giaime  Italy
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Default Simple EL84 PP design needed

Hello there!!!

I've got the iron to build an EL84 stereo PP tube amp. I've got an old stereo tube amp that I'm cannibalizing for this project. It has a power tranny (don't know voltage or current ratings), a GZ34 recto, an ECC82 as driver and 2 EL84 for each channel, and good output transformers (judging from the size and the construction, but don't know the impedance). Also it had a complete pre (including phono stage) with another 2 ECC83. Since I want only a power amp, I'll eliminate these. The filter caps were rated at 350V, so I will expect to see 300-320V after the rectification.

What I want is an extremely simple design (no ccs and similar), cathode biased, pentode/triode switch, little NFB, driven by either ECC82 or ECC83, either two (each channel gets one) but it would be better to have only one to drive both channel. I would like to keep it tube rectified.

It will take the output from an SS integrated amp preamp section (for now it's a NAD3020), but I plan to add a tube pre later. So input sensitivity should be around 2Vrms for full output.

Can anyone help me? I've searched the forum but I can't find anything really simple...
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Old 12th September 2005, 05:21 PM   #2
cerrem is offline cerrem  United States
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Take a look at the Fisher SA-16 and the SA-100 schematics.....
These are as simple as it gets for EL84 amps...but descent quality...
The power supplies on the SA-100 used massive voltage dropping resistors.....Obviously you can eliminate and simplify the power supply for your application....

Chris
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Old 12th September 2005, 05:28 PM   #3
Jaap is offline Jaap  Netherlands
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Default I am sorry

but you have to enhance your searching abilities.
There is another active thread that gives everything you asked for:

Searching for simple circuit

It is about the so called poindexter amp. 6v6 can be exchanged by el84
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Old 12th September 2005, 06:31 PM   #4
Giaime is offline Giaime  Italy
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Default Re: I am sorry

Quote:
Originally posted by Jaap
6v6 can be exchanged by el84
I don't think so. They are different tubes (6V6 is not a pentode btw), my request was very precise. I asked "with this stuff what schematics should I follow"? not "which amp should I build".

I'm thinking of designing it by miself, it shouldn't be hard.
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Old 12th September 2005, 06:40 PM   #5
SY is offline SY  United States
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Why ECC82/83 in particular? ECC83 can work OK as an input tube, but is pretty weedy as a driver. ECC82 has rather high distortion. Other tube choices are cheap, why not consider them?
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Old 12th September 2005, 07:07 PM   #6
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Here is a simple schematic for the EL84, and you can sub the 6EU7 with your ECC83. In this circuit they will do the job nicely. Very simple, few parts, and surprisingly effective.

http://members.tripod.com/~gabevee/maggie.html

Skip all the text and go to the center of the page. You will see one half of the two channels. Just make sure you tie all four output tubes's cathodes to the one 100 ohm paralleled with the 22 uF cap.

You can make the power supply any way you desire, or follow this one:

http://members.tripod.com/~gabevee/mypwrsup.html

The first and second schematics use indirectly heated and directly heated cathodes respectively. With the components used, it is a most effective power supply.

Hope this helps!
Gabe
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Old 12th September 2005, 07:23 PM   #7
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if you Google "EL84 Push Pull" you will come up with a ton of designs. Here's one I liked: Claudio's site
http://www.bonavolta.ch/hobby/fr/audio/el84.htm
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Old 12th September 2005, 08:20 PM   #8
Giaime is offline Giaime  Italy
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Thanks!!! I will go throught them and see what's the best for me... thank you all!
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Old 12th September 2005, 08:37 PM   #9
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try typing -> russ valveamps on Google theres lots of schematics for all sorts.

richj
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Old 12th September 2005, 08:59 PM   #10
Giaime is offline Giaime  Italy
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Thanks, but can someone point me to a design that uses a SINGLE triode section (of whatever tube) to drive a couple of EL84??? All those designs show many stages, some of them also (aaargh) tone controls, instead I want to keep the thing extremely simple. I need a driver stage with only 1 triode section that does the phase splitting and also the gain to drive properly a couple of EL84s.

Thanks so far!!!
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