New build: Micro Pig Deluxe

[Lynxtrap]

I've got plans for a new project.
It started with a chassis from a Behringer mic preamp that I stripped. It's two rack units high, quite a big box.
I thought I would limit myself to the confines of that box and get everything to fit inside, including the tubes. So I started to think "micro"
I'm also limited to a total of six pots. Lots of switches, but I'll save those for later.

I've long been fascinated by the preamp in the Marshall 200 a.k.a "The Pig". So that's one channel and the other is similar to a brownface Deluxe.

I have transformers in mind, and will probably have B+ at around 300V. As I'm also using this as an opportunity to learn how to make schematics using software, I've only managed to draw the audio circuit so far

Thought I'd upload it anyway for possible comments and critical evaluation...

[xtian]

I've not seen that topology before. Very interesting!

[Tony Bones]

Looks like a cool project! I'm eager to hear what you think of the pig channel.

[Phil_S]

Did you consider self-split for the 12AU7 output tube? You'd get to skip the PI and a bunch of parts. I'm not sure it will make much difference.

[Lynxtrap]

Did you consider self-split for the 12AU7 output tube? You'd get to skip the PI and a bunch of parts. I'm not sure it will make much difference.

Not really, as I'm not really familiar with that. I'll look into it. Any drawbacks with self-split?

EDIT: Looking at some schematics, I figure there would be less output power from a self-split stage? I was actually considered going the opposite way, adding another output tube to double the power.

[Lynxtrap]

Here is a complete schematic, first revision. Please comment if you see something funny.

TF Micro Pig Deluxe rev1.jpg

[Phil_S]

I'm not sure what sort of tonal contribution you'd like from the output tubes. As far as wattage, you've got options.
A pair of 12AU7 is OK and so is a pair of 6SN7, basically the same tube in a large bottle, but able to run with B+ up to 450V.
You might consider using the ECC88. JJ makes one. You'll get 2W in self-split.
If you want a low output pentode, troll eBay for EL95's. Good brands like Telefunken and Mullard can be had inexpensively. This tube has a very light draw for the filaments.
Stepping up, maybe a 6BM8, but has layout considerations because it's a triode/pentode package.
There is always 6AQ5 (7-pin) or 6V6.
The thing is, there won't be much difference in volume from 2W to 4W, or for that matter from 1W to 4W. You can probably compensate by using an efficient speaker to squeeze out more.
Just some food for thought. Good luck with it.