Simple EL84 PP design needed

[Giaime]

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...

 

[cerrem]

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

 

[Jaap]

I am sorry

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

http://www.diyaudio.com/forums/showthread.php?s=&threadid=63905

It is about the so called poindexter amp. 6v6 can be exchanged by el84

 

[Giaime]

Re: I am sorry

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.

 

[SY]

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?

 

[Gabevee]

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

 

[jackinnj]

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

 

[Giaime]

Thanks!!! I will go throught them and see what's the best for me... thank you all!

 

[richwalters]

try typing -> russ valveamps on Google theres lots of schematics for all sorts.

richj

 

[Giaime]

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!!!

 

[Tom Bavis]

You could buy the PCB from diytube.com and just drop in your tubes - 1/2 12AX7 for first stage, 1/2 12AU7 for phase inverter, push-pull EL84. Both tubes split across channels. It's the Dyna 35 crcuit: Dyna 35 (The 7247 used in ST-35 is 1/2 12AX7, 1/2 12AU7)


The simplest circuit is the compact amp - but low gain, lower output. output stage is phase inverter... Compact amp Oh yeah - 6C4 is 1/2 12AU7.

 

[richwalters]

Can't get much simpler than zthis one

richj

 

[Giaime]

It could be. Thanks. I've realized that I need a whole double triode to properly drive the EL84s. Given this, I will select a proper schematics. I particulary appreciate separate cathode resistors for the output tubes.

Thanks to all!

 

[Gabevee]

Well, if you look at the schematics with the single phase splitter tube, if it is connected to the preamp tube through a capacitor, then you can simply remove the first stage.

But alas they are generally direct coupled to the first stage.

There is another way where the output tubes do their own phase splitting. I saw that somewhere on the web... just can't remember where.

I will try to draw something up quickly or find it for you.

Gabe

 

[zobsky]

There is another way where the output tubes do their own phase splitting. I saw that somewhere on the web... just can't remember where.


Gabe

did you mean this http://www.diyparadise.com/simpleel84.html ?

 

[Ejam]

Simplest EL84 Amplifier

This is "one" of the simplest EL84 amplifiers. Having built this amp, I can attest that it gives great sonic performance in comparison to vintage designs. You can change the input tube to a 12AX7 if you like but you will need to adjust the cathode and anode resistors to suit. The only drawback is the phase splitting choke (use either the Electraprint nickel or M6 version as shown or the Magnequest EXO173 permalloy or M6 version) which is expensive (prices vary from about $50US to $100US each). In its favour, phasing splitting is superb. Attached is the schematic. Hope this helps.

Ejam

 

[zobsky]

Re: Simplest EL84 Amplifier

This is "one" of the simplest EL84 amplifiers. Having built this amp, I can attest that it gives great sonic performance in comparison to vintage designs. You can change the input tube to a 12AX7 if you like but you will need to adjust the cathode and anode resistors to suit. The only drawback is the phase splitting choke (use either the Electraprint nickel or M6 version as shown or the Magnequest EXO173 permalloy or M6 version) which is expensive (prices vary from about $50US to $100US each). In its favour, phasing splitting is superb. Attached is the schematic. Hope this helps.

Ejam

no phase splitting choke in your attachment,.. unless my eyes are playing tricks

 

[Ejam]

Sorry about that

Disregard the previous attached schematic. Was a bit too rushed to check. Correct schematic is attached.

Regards

Ejam

 

[Gabevee]

did you mean this http://www.diyparadise.com/simpleel84.html ?

Yavol! Yes, that is one that I saw. I think I actually saw one in the online magazine tubecad.

Gabe.

 

[skyraider]

hi,

http://www.diyparadise.com/simpleel84.html

I just completed this one two weeks ago and it really rocks!

It couldnt get any simpler.

If you browse further, there is a version with ccs in the cathode. The extra effort is worth it, especially in the bass department. With a mere 15 watts, it beats the hell out of many higher powered gears.