• E3443.png

    WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.​

EL34 SE, direct coupled

Thanks, I ll try to learn obout 7591 . 813 transmiting pentode is very interesting too, representing easy job for driver tube and could give 20 w in triode mode.BUT ... a good output tranies of that power are too expensive , and I don t have directcoupled schematics for it. I m newbie , so I can t calculate desired cirquit ...yet. Thanks again.


2006-09-04 7:39 pm
c'mon, guys ?!

nobody on a direct coupled EL34 ?




Ok, so I found this....

That cap isn't in the signal pad

(or is it? someone once told me;
"anything in there affects the signal")

but it seems direct coupled, and using 12at7 & el34

will this be any good ?

Cheers again !


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2006-09-04 7:39 pm
OK, sorry for the above post...

I looked closer and saw my mistake;
half #1 of the 12AT7 is actually driver stage, coupled via
the cap, half #2 of the 12AT7 is for distorsion purposes...
so no good for my apllication :D

I found attached shematic !

Now this IS dc-coupled but it uses a 6H23 tube, wich would be
close to an ECC88...

can this schematic be re-worked for a 12AT7 / ECC81 ?




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2006-09-04 7:39 pm

not to completely avoid caps,
(I do not think it's possible)
but surely to minimize their effect by reducing their number...

So far I only found one schematic using an 12at7/ecc81,
but this one isn't DC coupled...

still a nice schematic, I think




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This is a schematic of my current amplifier. You will have to play around with the biasing of the EL34, increase the current, to get the maximum power out of them. The TFA 204 transformers that I used saturate at 60mA. I don't think I have ever seen a DC coupled EL34 amp but I think you could do it with a triode strapped el84 as your input tube.


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2004-06-15 10:34 am
CD player to EL34 direct drive

THis is a noob question. Is it possible to ommit the tube driver stage and drive it directly from CD player output? How much voltage swing should present at the input of EL34 in order to drive it to full power in SE mode? Can you help to explain?



2003-11-11 11:06 pm
simple way of looking at it is to see the el34's bias voltage. if the grid is biased -30V at idle, it will take 30V peak input to drive it to 0V (maximum, for this discussion), which will also generate max. power (ignoring loading).

so a 2Vrms CD player output needs some additional voltage gain to drive it to full power.


2006-12-30 11:55 pm
Furthermore, when the grid goes positive it will draw current and become a very difficult load. Not to say that an op-amp will drive it there but the stage before the output generally needs to be tough, preferrably with a low output impedance.

Quite often, a driver with gain followed by an output stage with an output transformer will have a net gain somewhere near one, anyway.


2006-09-04 7:39 pm
G said:
I don't think I have ever seen a DC coupled EL34 amp but I think you could do it with a triode strapped el84 as your input tube.

That's a nice idea !
I always liked the sound of an EL84...

...I wish I knew how to design that

But by the way,
does anybody have the schematic of the EL34 version of Alex Kitic's RH84 for me ? (RH34SE)

Elsewhere on this site there's multiple mentions of its existence,
but the schematic is nowhere to be found...




2002-08-15 10:16 pm
There is a direct coupled version of Alex kitic's RH6550/RH88 which would be just what your looking for. Unfortunately it uses a huge wasteful cathode cap on the 6550.

I was just searching for the schematic, but it looks like Mr Kitic has taken down the site. He always struck me as a rather diagreeable fellow so he's probably taken his toys home.

How about this for the KT66.




2006-09-04 7:39 pm
Hi Shoog,

I understand and follow your feelings regarding Mr. K. ;)

However, his RH84 design is very nice indeed and I've been
listening to that one for a loooooong time and still convinces me

By the way, was it you who did a PP-version of the RH84 ?
I like the idea behind that....

But anyway, back on-topic;
I think (although I cannot "calculate tubes" very much),
that a EL84 as drivertube would be a solution to the
difficultly-driven '34 question.

I seem to recall reading somewhere about EL84-driving-EL84
but don't know where ?!


wasn't it somewhere in the Meta Gizmo files.... ?
I'll have a look....