SE EL34 schematic HELP: from two 6SL7's to One?

[ambience exists]

Howdy folks,

Here is an EL34 schematic I would like to build, but I was wondering if there was a way to change the circuit to just one 6SL7 (as it is a dual triode) to drive the EL34's instead of running the two sections in parallel as shown.

http://angela.com/stereosingle-ended...amplifier.aspx

Could someone help me figure this out?

[leadbelly]

Very easy to do. You build one channel using one half of the 6SL7, using the 6SL7 pin numbers outside the parentheses. Then, build the other channel using the other half, using only the 6SL7 pin numbers inside the parentheses.

Just one promlem...IMHO it's a bad idea. The 6SL7 is wimpy tube with low transconductance. The designer doubled it up for a reason, it was not some cosmetic whim.

[ambience exists]

now how about swapping the 6sl7 for a 6sn7? What would that do to my component values?

Or am I just causing too much mental trouble and should just build the dang thing the way it was designed.....

[Miniwatt]

Originally posted by ambience exists
Howdy folks,

Here is an EL34 schematic I would like to build, but I was wondering if there was a way to change the circuit to just one 6SL7 (as it is a dual triode) to drive the EL34's instead of running the two sections in parallel as shown.

http://angela.com/stereosingle-ended...amplifier.aspx

Could someone help me figure this out?

They are not run parallel, the schematic shows the complete amp with two separate channels, each driven by one half of the 6SL7

[ambience exists]

look closer at the image- the numbers by the lugs have numbers in parenthesis which is the other half of the tube. There is an asterisk over to the right which says that the two triodes in each tube are run parallel. I am assuming that there would be just a simple wire from say the cathode of the first section to the other section.

[leadbelly]

Originally posted by ambience exists
now how about swapping the 6sl7 for a 6sn7? What would that do to my component values?

A 6SN7 doesn't have enough gain. This isn't Scrabble. You don't design an amp by seeing what letters you have.

Originally posted by Miniwatt
They are not run parallel, the schematic shows the complete amp with two separate channels, each driven by one half of the 6SL7

Your was a little premature. RTFS

[Miniwatt]

Originally posted by ambience exists
look closer at the image- the numbers by the lugs have numbers in parenthesis which is the other half of the tube. There is an asterisk over to the right which says that the two triodes in each tube are run parallel. I am assuming that there would be just a simple wire from say the cathode of the first section to the other section.

I'm sorry, you're right, I didn't look further than the schematic. Let's just say I wouldn't draw it that way

[aardvarkash10]

Originally posted by ambience exists
Howdy folks,

Here is an EL34 schematic I would like to build, but I was wondering if there was a way to change the circuit to just one 6SL7 (as it is a dual triode) to drive the EL34's instead of running the two sections in parallel as shown.

http://angela.com/stereosingle-ended...amplifier.aspx

Could someone help me figure this out?

'sl7 drives mosfet follower, drives EL34...

[JPeitzman]

Plugging in a 6SN7 would indeed change your component values, but as was mentioned there probably wouldn't be enough gain. Unfortunately, true, you cannot just plug it in because it too is an octal tube. The above is a good recommendation though, having the SL7 drive a FET to drive the EL34. You could also do a mu stage with a pair of depletion FET's or a nice juicy pentode (D3a comes to mind, or 12HG7 maybe).

This is a very similar design to Tubelab's Simple SE, you could look into that as an option too. It just uses a current source loaded 12AT7 instead of the 6SL7 to drive just about any common octal power tube (EL34, KT88, 6L6, etc...). There is a ton of support around for the Simple SE, lots of builds floating around. Great easy to build board that is open to options; cathode feedback, triode/UL outputs, all sorts of different bias settings, LED biased 12AT7 (losing a cap and a resistor), maybe removing the 10M45 and rolling some current sources (a la Pimm, Camille, or others), tube rolling, the fun just can't end.

http://www7.taosnet.com/f10/mustage.html

http://www.tubelab.com/

Attached is the dual depletion FET source, for a "FET mu stage" you would take the signal from the "Low Z Out" attachement. The diagram is thanks to Poinz by the way.

Cheer

James

[Tubes4e4]

Hi,

driving the 100...150pF of Miller capacitance of a trioded EL34 to (a little bit more than) 56Vpp as per the Angela circuit cannot be done with a single section of a 6SL7 with a reasonable slew rate. You will encounter high freq roll-off way too early, except you use an AM radio as a programme source.

The paralleled sections as shown will do okay, especially considering the limited bandwidth capabilities of the suggested 125ESE OPT.

Again, considering the limitations of that OPT, some suggestions already given here in this thread like MOSFET source follower drivers or mu-stages are thoughtless and unneccessary overkill.

Actually, a "mighty" driver would "unmask" the shortcommings of the cheap OPT: With a "mighty" driver in this zNFB design you would get all sorts of phase shifts at upper freqs. With the circuit as is, you get a smooth and reasonable high freq roll-off.

The Angela circuit - as is - sounds surpirisingly good to me (if you like "singing" amps), not only considering the lowish component price/investment. Actually, it is a good example of a straightforward and homogeneous implementation with limited ressources.

Bandwidth plot of the original circuit (using two 6SL7 sections paralleled) attached.

Regards,

Tom Schlangen