would this work? SE EL84 circuit

[bikerhifinut]

Just listening to my RH84 after a bit of tweaking.
I think I may have had a bit of "tracking" between valve pins on the ECC81 sockets, I cleaned it up after measuring a slight amount of leakage between pins with the DVM. This may well have been causing the circuit to underperform.
The transformer is tweaked up by using it on the 210Volt tap, I checked with the friend who supplied it and reckoned that it was fine to do that without harming it as it's insulation was designed to take 250V AC, plus the transformer is being under run current wise on the primary, being designed for use with a radiogram with 9 valves and I'm only running 3 heaters off it. In future I may try and squeeze a bit more HT (B+) by using a pair of silicon rectifiers, but for now I am enjoying the sound.
The CCS is reinstated, I always used the zener diode feed to screen grid, and cathode voltages are running around 7V, which is fine I reckon as I am only getting 250V HT (B+) with the PSU as stands. I lost 20 odd volts through the choke (10H @ 100mA Danbury), but I feel that was worth it for the totally silent background, no hum at all. This little baby is quieter than my WD88VA and the KEL84 I had. No mean feat for a single ender with AC heaters!
It sounds very "Meaty" now that its running right but theres a sweetness to the sound especially on vocals and accoustic instruments. I can hear details like breathing and rustling clothing on my CD copy of "9 Dead Alive" by Rodrigo y Gabriela.
Thanks Alex for the design, its beautifully simple and most definitely "Less is more" with the RH84.
Anybody thinking of having a go at a single ended EL84 amp should consider this, simpler and less fussy than a 3-3 and with a sensible sensitivity.

Andy.

[Alex Kitic]

Swapping the tube rectifier for silicon diodes will probably add to the learning curve - you will most certainly immediately find out why I prefer tube rectifiers In simple words - better not... stick with tube rectifiers.

As for the voltage, I see from you explanation that you have added some 47 ohm resistors behind the choke. The power supply schematics of the RH84 (and in particular those proposed for the rev2) foresees just one choke for both channels, and that's it. The first cap might be around 47uF, the second around 220uF... anyway, you are loosing some V across those resistors, and also some sound quality along the way.

[bikerhifinut]

Just thought I'd add an update.
The RH84 based SE amp is working luverly and hasn't missed a beat.
I've been using it in the main system and at low to moderate volumes its got a delightful sweet nature, especially on accoustic instruments and voices.
I don't always miss the extra "thrutch" of the KT88 amp mainly at the LF end of things. It's very noticeable when I plug the big WD amp in, but in general I find myself liking this little SE baby.
It was intended as a "garage amplifier" but it's too good for that! Wish I'd built it before those speakers were on offer recently as they would have probably suited a low power amp.


After I gave it a rework and used a choke in the PSU it's also completely hum free............... unbelievably so.

I got to thinking the transformer that gave me all that grief due to supplying far too much B+ would have been ok if I used a choke input PSU rather than capacitor input. So thats on the drawing board for another amp project.
That will be likely another RH84 probably based on Alex's "Universal" design.

Andy.

[bikerhifinut]

a couple of pics of the RH84

A.

[Alex Kitic]

Actually it is quite good looking. I always like to see the "diamond" or romboid pattern.

If you need more power, you might consider building the Universal. Besides being universal and letting you play with tubes, it has loads of power and plenty of authority in the presentation of music. Users have compared the subjective loudness and apparent power to 25W PP amps... a Dynaco 35 W pc has slightly more power but lacks bass and definition in comparison.

Believe it or not.

[bikerhifinut]

Originally Posted by Alex Kitic

Actually it is quite good looking. I always like to see the "diamond" or romboid pattern.

If you need more power, you might consider building the Universal. Besides being universal and letting you play with tubes, it has loads of power and plenty of authority in the presentation of music. Users have compared the subjective loudness and apparent power to 25W PP amps... a Dynaco 35 W pc has slightly more power but lacks bass and definition in comparison.

Believe it or not.

I believe it Alex.

I will have a crack at a higher power SE when life here is settled and I have built the 2 ongoing amps I have parts for.

I have a notion to build a Universal with KT88/6550 purely because I have a good stash of them.

I just love the simplicity and elegance of the design Alex.

Andy.

[Alex Kitic]

Originally Posted by bikerhifinut

...and I have built the 2 ongoing amps I have parts for.

I have a notion to build a Universal with KT88/6550 purely because I have a good stash of them...

That is probably part of the learning curve: I have always been much more focused.

You only need so many amps, thus commitment in building an amp means time and space, and of course shelf space.

I have always tried avoiding sub-optimal choices. Parts are relative, they can be used in a variety of applications.

While I still design "dedicated" amps, I have chosen the functional approach. The universality of the RH Universal and RH-TTA is an example.

The only dedicated amp I currently have on my shelf is the RH300B, but that is a particular case. I can actually use the 300B in the RH-TTA, and if I had really efficient speakers I could probably forget about the additional power the RH300B has (double the power, actually).

Thus the Universal is not just about 6550 or KT88, but EL34, 6L6, KT66, etc. - I like to call it "Liberty", as it gives you freedom of tube choice and combination.

So much for a learning curve...