Hiwatt Genes

At it again. Having built a vintage Fender-based circuit (the Scarlett) and another one incorporating slightly more modern ideas (the 2SE), I've gotten interested in the Hiwatt story. Mark Huss's website provides useful history and technical information, and of course, I love the sound of the classic rock and roll recordings made using these amps from the 60's and 70's. So, building something with Hiwatt genes, that gives me yet one more distinct guitar tone to choose from, seems like a good next project.

But without making a complete clone - sourcing identical parts and making an exact copy of the original - can one actually build something that sounds similar to the original? I'm doubtful, yet I don't what to invest a lot of money in getting those parts (e.g. the transformers are $300 - $400 each) when I have a bunch in basement, left over from the original cache I received from Michael last year. There are, however, some design features and build techniques I can use that I think may contribute to a Hiwatt-like sound.  I am also interested in having an amp that uses lower powered output tubes, such as a pair of EL84s (compare about 18 watts output power to the 35-40 watts produced by the 6L6 tubes in the Scarlett), and there are plenty of good power section designs out there to draw from. While Hiwatt did eventually design an amp around these smaller power tubes (SA20, Custom 20), that wasn't until after the founder passed away and the company was sold in the late 80's, so these newer amps and don't really have the classic sound of the amps they produced in the 70's. In any case, I'm looking into a design that might incorporate those things.

Good schematics of various Hiwatt models can be found here and here, and there are lots of pictures of originals and good reproductions to draw from. I'll build a head-only version with a pre-amp section based on the DR504, with a selectable built-in overdrive option based on the DR Overdrive Lead (DROL). There's a Hiwatt-like kit that was made by Trinity Amps that has some of the same features I'm interested in, so I'll borrow from that design and try to use as many of the early 70's classic layout and circuit features as possible, while reducing the power of the output section from the usual 50 watts to 20 and adding a few other features, like a transformer-tapped Line Out (for bi-amped wet-dry effects option), DC-elevated filament heaters to reduce noise, and separate and blendable input channels.

Here's my schematic of the hybrid circuit I've developed, with notes: