Philco 3610 into Fender Champ guitar amp

After I listed and sold an "RCA 521" Champ I was asked if I can build the same amp in a given cabinet. Soon I got a Philco 3610 code 121 radio in my garage, the one made in Toronto in 1936! That was so far the oldest one I touched, with 6 pin tube sockets and massive steel chassis. We agreed with the owner that I create an electronic part of an amplifier and he would take cabinet and speaker portion.

As usual, I didn't take a "before" picture, so posting the one from a Radiomuseum.org - great source of information, pictures, and schematic for many tube radios.

I managed to clean the chassis and other metal components to the acceptable state. Original power transformer turned out to be good as well. With this I decided to keep as much of original radio as I could and build a Champ circuit around.  

Power circuit

This type of a radio didn't have a permanent magnet speaker, utilizing a field coil instead. To re-use it's power transformer for a guitar amp you'd need to drop about 80V of extra DC voltage. I put a 10W 2.2K resistor in series, been mounted on a strip of aluminum. This is fine with a Single Ended amp schematic, when consumed current is pretty much constant. Also, the reservoir capacitor must withstand about 600V DC. The workaround for this is to install standard 450V capacitors in series and parallel them with voltage balancing 300K resistors. With all of those the power section takes about a half of overall circuit.

Tone stack and control knob setup

In search of a tone stack that can vary from a high "brightness" to a low tone, I came across this amazing online version of a legendary Duncan Tone Stack Calculator. After playing a bit with it I opted for a Princeton 5F2 stack. I think that's what I am going to use in any two- or three- knob setups.

The three knobs on the picture below are Gain, Tone, and Master Volume. I'm applying same proven technique to extend potentiometer shafts to desired length. 

I kept a dial scale and put an input jack instead of a tuning knob, so no need to drill an extra hole on the front panel. 

Decoration 

With no reason to care about an old 6-pin tubes, I gently drilled a hole in all tube's bases and inserted a small amber LED in each to make it look like it is glowing. Isn't that amazing?