Interesting, Although we'd be looking at maybe 1/4W if I used the voltages I'm aiming for if I'm reading that sheet right...
I've decided if I can't approach ~1/2W or more, I feel the effort would be more than it's worth considering I could easily get about 12W solid-state for half the price of an output transformer.
If I feel like going up to 90V... Well, that's a different story entirely. The preamp has been built to withstand voltages of a "normal" voltage preamp so there is always wiggle room. I'd still like to keep it sub 50V though.
The preamp stage of the Duncan amps Blues 112 runs off 56V. Not quite as highgain as you want but worth looking at.
Right... Well I've come up with some numbers, What I wanted to do just isn't possible in the way I wanted it done, but thank you all for pointing me to various resources. It helped me get to the point I could understand it wouldn't work and why.
Looks like I'm going solid state... At least until I've used up these 12U7's and have to work my way through the 12AX7 stash.
Looks like I'm going solid state... At least until I've used up these 12U7's and have to work my way through the 12AX7 stash.
12U7 ?
There's a number of starved anode designs around 12AU7s which work down to 12V (not built one m'self but apparently provide decent distortion).
If you parallel both halves of a 12U7 you'll get 6K plate, which with two in PP should just about work with a 1.25W line transformer with 8ohm hooked up to the 4ohm tap (16K P-P, IIRC). Use another 12u7 as driver & phase invertor ; a fourth as input/tone stack and you're done. A whole 100mW flat out, or thereabouts.
If you need gain, stick a TL-072 in front just like the Blues 112 and leave a cold cathode later up the gain chain. If you need volume, add a solid state amp-in-a-chip afterwards.
(Actually, that's one weird looking datasheet. I wonder if they're specially selected 12AU7s??? )
There's a number of starved anode designs around 12AU7s which work down to 12V (not built one m'self but apparently provide decent distortion).
If you parallel both halves of a 12U7 you'll get 6K plate, which with two in PP should just about work with a 1.25W line transformer with 8ohm hooked up to the 4ohm tap (16K P-P, IIRC). Use another 12u7 as driver & phase invertor ; a fourth as input/tone stack and you're done. A whole 100mW flat out, or thereabouts.
If you need gain, stick a TL-072 in front just like the Blues 112 and leave a cold cathode later up the gain chain. If you need volume, add a solid state amp-in-a-chip afterwards.
(Actually, that's one weird looking datasheet. I wonder if they're specially selected 12AU7s??? )
The 12U7 is super-similar to 12AU7 but the materials are selected and processed differently. If you throw random AU7s in a 12V circuit, the various contact potentials will all bias different. Some work, some suck, some silent. U7 has the low-voltage potentials under control, apparently at the cost of not tolerating high voltage.
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