Help with oddball 3XEL34 output section?

[jbefumo]

Hi All,

Recently got back into hobby electronics after many years and am setting out to build a guitar amp. I've built several tube amps in the past, but always by following a proven schematic. This time I'm looking forward to trying my hand at a bit of designing as well.

Discovered MultiSim, and am in the process of modeling my dream amp before breaking out the soldering iron. (Amazing program, btw).

Anyway, I discovered this somewhat oddball (to me) design, and have been playing around with it in the simulator. Here's the design: The Tube CAD Journal: Out of Control: The missing sonic controls

I've got the simulation working, however, the RMS of the output signal is about 1/20 that of a standard EL34 Push-Pull output.

My electronic chops are a bit dusty, and were never that great to begin with, so I'm trying to work though this design on my own, but any hints would be greatly appreciated. My main questions are: Is this low output an inherent aspect of the design? Or do the component values need to be tweaked?

Second, any comments about how this might actually work in a guitar amp? Sounds interesting in theory, but I kind of wonder why nobody else is using it?

Thanks.

Joe

[octal]

Did your simulation allow for biasing the output tubes at different points AND applying different amplitude, yet out of phase AC drive signals to the output tubes?

From the original article:
>
The drive requirements for this amplifier differ from a standard push-pull amplifier in that the top output tube needs to see a much larger grid swing than the bottom tube.
>

It's an interesting idea. Do you find you prefer the sound of SE guitar amps, but want the option of more power output?

Nathan

[jbefumo]

Yes, I was able top apply the different bias values and mess with the phase inverter to get about a 10:1 ration between the RMS values of the output signals. I've mainly used P-P amps, though I did own a Vox AC30 a lot of years ago. Mainly thought it might be an interesting thing to experiment with. I THINK there's a way to get the simulator to accept an external signal and direct the output through hardware as well, which would make it ideal for 'tinkering' before committing anything to solder.

Joe

[octal]

I just noticed one other thing. The EL34s are triode connected. Right there, that's going to make your power output be a fraction of what it would otherwise be. I'm not sure this circuit would work with Pentode connected EL34s... I don't think CCSes play nicely with pentodes. Could be totally wrong about that though.

Nathan

[jbefumo]

Ahh, hadn't caught that. Would you guess the end result would be in the 15-20W category?

Would there be any particular considerations for this kind of topology with respect to higher-than-average voltages? The chassis/transformers I'm going to use are from a Sundown SD1012 that purported to make 100W with 2 6550s. Not sure how accurate that might have been, but the supply voltage is 497, so I guess they were running hard?

I'd like to avail myself of whatever the platform has to offer, but plan on shooting for something in the 35-45W region. Not sure yet if I'm going to use EL34s or perhaps KT66s.

Joe

[octal]

I think triode connected PP EL 34s are good for about 20W... I think this 3 tube configuration might reduce that though. It lies well outside of my experience!

Nathan