EL84 SE design recommendations?

[audiousername]

Sounds like you're enjoying the music. And after all that's what matters, whether you have Black Gates or not.

[Alex Kitic]

Usually, what we find at first is the best... although we seldom recognise it.

If you ask (me), I would say that you should bild the RH84 amp you found as an interesting choice among the first few amps mentioned... and for the moment, stick to that.

How do I know that it's any good? Well, it's my brainchild, and I also did build it and experiment with it with a whole variety of driver tubes etc.

What this design lacks is commercialization and too much modesty: I should have named it "the slayer of the Zen", and that would do for everyone...

If you need any help, just e-mail me.

Best regards to all...
Aleksandar
(tired of being modest and reading lots of mumbo-jumbo by people who did not give too much of a tought to what they are saying/writing)

[planet10]

Originally posted by Alex Kitic
If you need any help, just e-mail me.

I'm still very much a rookie when it comes to this stuff....

What differences does the feedback between the plates do?

and

I note that the screen is not bypassed to ground?

Also, what other driver tubes did you try...

dave

[Brett]

Originally posted by planet10


I'm still very much a rookie when it comes to this stuff....

What differences does the feedback between the plates do?

and

I note that the screen is not bypassed to ground?

Also, what other driver tubes did you try...

dave

It's all explained here.
http://www.tubecad.com/march2001

and also look at Gary Pimm's site for his PP47, which cronicles the progress from a triode driver to a pentode (I only built the pentode).

[Alex Kitic]

The Rfb between the anode of the output tube and the anode of the driver tube makes the whole circuit behave in a different way than usual. The driver acts as a current amplifier, while the output tube acts as a current/voltage converter.

Yes, John Broskie wrote an article on the subject, concerning mainly 5965 as driver and 300B as output tube... but that is a slightly (if not completely different cup of tea). When it comes to the other mentioned design explanation, I would not know, I have to look for it on the web.

Originality? Well, it is my opinion that "hot water" was invented a long time ago, especially when it comes to electronic tubes and circuits. Still, I would say that this approach has something of its own going on... therefore I do consider it original.

There is mention of the Zen amp by Decware, and I believe I mentioned something about renaming my amp "The Slayer of Zen" in order to make it more popular. Does anyone want to know why this amp is muuuuuch better than the Zen?

Regards to all!

[planet10]

Originally posted by Alex Kitic
There is mention of the Zen amp by Decware, and I believe I mentioned something about renaming my amp "The Slayer of Zen" in order to make it more popular. Does anyone want to know why this amp is muuuuuch better than the Zen?

yes

[Stixx]

Zdravo Alex,

I'd like to know that, too!
I once had a zenamp for testing, and I liked it alot. I only was worried that power would be not enough, so I am listening via a modified Leak Stereo20 now.

Ciao,
Oliver

PS Isn't Zemun a suburb of Belgrade...?

[Yugo]

Another tube dude and great guru from Zemun!

http://www.tubeaudiolab.co.yu/

Dobrodosao Alexandre!

Regards,
Yugovitz

[Alex Kitic]

The reasons why the RH84 is far better than the Zen:
1. Driver tube
In the Zen, the driver tube is an ECC88, which by definition is not the best and most musical audio tube (OK, arguably and argumentative) -- but the main issue is the operating point for this tube. In order to function well, the ECC88 generally needs some 10mA of current, while in the Zen such conditions are not met.
The RH84, on the other hand, has an ECC81 (or any equivalent) as driver, which tube is much closer to being a true audio tube (argumentative) -- the issue being that in this case operating point requirements are met and the tube does not run a low current (for those who know what am I writing about, a bad choice of operating tube is letting it work on the low very curved part of the curve as shown in datasheets...).
2. Power
The Zen is presented as 5W per channel, which might only be P.M.P.O. like chinese cheapo speakers for PCs. In effect, it does only afford some approx. 1.5W RMS, since the tube is operated in triode mode.
On the other hand, the RH84 was designed to give 4W RMS at 1% distortion (approximately) -- and does so by operating in pentode mode. Some might immediately argue that in this case, the Zen must have a better sound since it does not operate in pentode mode or adopt NFB, but those some would be wrong, since in the RH84 the tube sounds almost identical, not to say identical in pentode mode and in triode mode (a switch might be implemented to choose from pentode to triode mode, in the latter case obviously disconnecting the resistor between the anode of the output tube and the anode of the driver tube, and obviously redirecting the connection of the g2 to the anode in order to make it "triode mode").
How is that possible? Let us skip momentarily a longer explanation and just say that there is (and should be) a huge difference between scribbling some schematic and eventually making it work, and on the other hand, doing some research and investing some time in really designing some amp...
3.
Power supply
The Zen does apply a tube rectifier to its power supply -- making it immediately sound better than if it were simple SS diodes. But, the power supply is not that sound, since chokes are not applied and the value of the capacitors and eventual smoothing resistors does not lead to a particularly low ripple on the B+. Of course, chokes are costly, are they not?! Come on...
The power supply of the RH84 is a completely different affair -- however you build it, you should stick to the guidance given on the schematics. With a tube rectifier, followed by even a simple combination like 47uF - 10H choke - 220uF, the ripple is much much lower than in the Zen, while the sound is also much improved by adopting even such a simple solution.
4.
Last but not least, of those issues that immediately get to the eye of the experienced viewer of schematics, there is a shared cathode resistor for both output tubes, meaning both output channels, in the Zen. I just cannot believe that... but that is what the schematics show, and what can be seen in pics of the interior. Well, if it is really true, we are talking about channel mixing, not channel separation: that such form of masking can lead to some mellow or interesting or whatever sound, can be immagined... but I truly do not know how to expect a soundstage from an amp that has poor separation?!
When it comes to the RH84, well, separation could be better only if the power supply was split as well and the amp built as monos... but beside that, no such design flaws (or elaborate plots to mask deficiencies caused by poor whatever wherever in the amp).

I sincerely believe that these 4 points are enough even for neophites to get a glimps of the differences between the amps in question.

Inflamatory? I do not think so. When it comes to those who like cloning amps, as they call it, just clone the RH84. For the others, who paid for their Zen and might now feel offended -- there are several simple solutions, like buying a choke and substituting a "smoothing" resistor with the choke they bought... exchanging resistors on the driver tube in order to achieve a better operating point... or stripping the nice chassis of the superfluous parts, adding a choke and remaking it as an RH84... whatever they choos, even sticking to their amp, is their own choosing now.

Regards to all -- for details of the schematic, I remind you to look for them on my site, www.tubeaudio.8m.com !

Regards to Mr. Tito, as well... Zemun rules!

[Alex Kitic]

Just a few words about what Zemun is, for those who would like to know...

To say that Zemun is a suburb of Belgrade, is simply derogative. Zemun is one of the several municipalities of Belgrade, and before WWII was a city on its own. In Austria-Hungary times, it was a border city of relative importance since it overlooks the Danube, just like Belgrade on the other bank. Furthermore, Zemun-polje might be a suburban area of Belgrade (and Zemun).

After WWII, Belgrade was enlarged by claiming marsh ground on the affluence of the rivers Danube and Sava. The new part of the city, quite large, is now known as New Belgrade, and has connected directly Zemun to Belgrade -- thus Zemun has become a municipality of Belgrade.

By the way, Belgrade has approx. 2 million inhabitants, which is quite large by Central-European standards.

Last but not least, Zemun "houses" quite a lot tube "gurus" and audiophiles... most certainly by coincidence -- but that does not stop me from calling it the Tube Capital of this part of the world. Some of these are quite known, like Mr. Vukusic. What distinguishes me is the fact that I am not at all commercial, meaning that my projects have never been sold or bought.

Maybe some day, when I emigrate somewhere else, there will be some "Kitic audio design", or the like of it. For now, strict hobby.

Regards to all, Alexandar