My goal is to create a single input version of the 1987 circuit which I can then use as a platform for modification, hopefully ending up with a second switchable channel based on a 2204 preamp with an extra gain-stage. But first thing's first...
Having the benefit of an aluminum brake, I was able to fold my own chassis from .06 sheet aluminum. It didn't turn out that pretty, but I'll just say it has a nice hand-crafted vintage look. It's plenty sturdy enough and it think it will do the trick.
Since I will be drilling the chassis myself, I started playing around with the 1987 layout (as shown in the Metro instructions) to create something that might better suit my needs. I added a little Hiwatt influence by shortening the ptp board and adding a second board for the plate connections. I also relocated the OT to the other side of the chassis to free up space. You will also notice an extra 9-pin socket, extra pots, and empty space on the board for the anticipated gain stages.
(Click picture to download high-res version)
Before I start drilling though, I figured it would best to ask a few questions and get whatever advice I can from here first. A few things that I'm wondering about:
1. In the Metro kit, the first filter can (F1) comes after the Standby switch. I have the filter cap right after the bridge rectifier, before the switch. To my knowledge this shouldn't make a difference and might in fact be a more correct way, but it doesn't hurt to ask.
2. For the heater wiring, I've aligned the tube sockets so that the heater wires will pass through horizontally in a straight line, being twisted above the rest of the connections to the tube sockets. I will connect the heaters to the V2 position, but no tube will be installed of course. What about the unused triode in V1? Does that need to be grounded or should I just leave it as is?
3. I have read that the preamp needs to ground in the same place as the preamp filter cap ground (F3). I have done this by running a wire from the pot grounding bus to the back of the chassis and onto the F3 grounding lug. Is this ok or should I ground to a closer point?
If you see any oversights I might have made or have any other advice for the layout it would be greatly appreciated. I'm fairly certain all the connections are correct, but I will be referencing the 1987 schematic and the Metro instructions during the build anyway.
Hopefully I don't catch too much flak for alter the traditional layout.
I look forward to sharing the rest of my build with the forum.
