quick OT question

[firemedic]

I have a 50W 2-EL34 OT (734-139)laying around. I'm thinking of putting it in my TOS, since my current OT is a 2-6v6 041318, using 6L6s. I'd like more headroom on the clean channel tho.
I already know I'll need an extra filament xfmr for the heater load of EL34s. And my pin 1s are connected to ground already.
My question is, would 6L6s work with an EL34 OT, so I could switch back & forth?

[HotBluePlates]

In general, yes.

How much extra power output you might get depends on the balance of B+ voltage, B+ current available, OT primary impedance and phase inverter drive voltage available.

[firemedic]

My real question is, how do 6L6s sound in EL34 amps?

[bobmegantz]

I tried a direct substitution (just adjusting the bias) and it sounded bad.  I'm not sure why, but I suspect it's not the OT, rather different gain/drive/fb requirements.  You should check the entire output stage design...

[jerrydyer]

I like 6l6 in my higher gain builds. more preamp overdrive than power. if I were doing a non master and wanted breakup I would use el34. 6l6  sweeter highs better lows. el34 midrange coverage, great breakup when pushed right.

[HotBluePlates]

My real question is, how do 6L6s sound in EL34 amps?

No, your question was, "can I use an EL34 OT with 6L6's in an amp that is now using 6V6's?"

There is not a lot of difference in the load required for 6L6 and EL34, so that change is not an issue. EL34's sound different than 6L6's, and have a higher Gm, so the 6L6 might require a little more drive voltage and bias, depending on other factors in the amp.

But if you are replacing 6V6's with either larger output tube, and want more output power, simply swapping tubes and/or swapping the OT may (or may not) be all you have to do to get more actual output power.

[firemedic]

I wanted some more headroom. I'm already running 6L6s into the 6V6 OT. I have an 8ohm speaker load but the output tap is set to 16ohms, which theoretically should get the impedance matched a little better.
I believe at high output levels I am saturating the little bitty OT. I don't want that. 
I happen to have a 3.7k primary 50W tranny from my old Laney. And some EL34s.
So in an effort to get my clean channel sounding clean, leaving the od to the TOS preamp, my thoughts were to upgrade to much larger "EL34" OT.

While I was at it I figured I could set it up so I could switch out EL34s with 6L6s.
If that is a bad idea then I'll forget about it & upgrade the OT AND the PT some time in the future. My PT is handling 6L6s just fine now.

[HotBluePlates]

I had been mulling this over for a while, ever since jojokeo's post about why he wasn't getting more volume/power when switching tubes.

The only way to get the idea across is to create a post showing how much power small and big tubes actually make, if you keep things the same, as well as how supply voltage, available current and load impedance factor in.

If you want more volume/headroom now, add more speakers (or more efficient speakers). Aside from that, for the output stage to make more power, everything needs to be upped to make a bigger power stage/amp.

For an (over-)simple example, you want more power, so you use bigger tubes. The bigger tubes could pass more current, but the old higher load impedance limits the current swing. You swap OT (or load impedance) to allow the tubes to swing more current, but now you run into the limited current available from your existing power transformer and B+ supply. So you tack on another power transformer, maybe to raise B+ voltage as well as available current (because more supply voltage yields more possible voltage swing; increasing current swing and increasing voltage swing works on the power equation from all sides). Your bigger output stage may require more bias to tame idle current at the higher supply voltage, so now it also requires a bigger driving signal to push the output stage to its full capability; maybe you need an alteration to the phase inverter, or a new inverter circuit. Now that your revised power amp makes more power, are your existing speakers up to the task?

The point of the example is that an incremental change may not get the result you want.

[firemedic]

Not only that, I'm not real sure about the quality of the big OT. I'm sure it's a cheap replacement for the old Laney- and I remember using it briefly in my 1st build and not liking the tone w/ 6L6s.
I think I'm going to wait awhile, then upgrade both transformers with Doug's iron. I'll use the little ones for an actual 6V6 P-P amp, for which they are intended.