adventures in Dumbleland: modular amp system

[matoni]

Hey all,
Fresh off my modded Vibro Champ build, i want to build the preamp section of a dumbleland special (serial # 009), schematic posted below) and I have a couple questions before I begin designing this preamp and a chassis (a 19 inch rack) to go along with it.

So this is the first build in my idea for a modular amp system. The idea is to get a rack unit and put all of these preamps in the rack unit with 1 or 2 power amps, kinda like Billy Corgan uses and discusses in the beginning of this video.

Question 1: is this possible? I currently have a JM 2 rock sig amp (clone from Ryan Colgan that I built), and I was thinking (for now) plugging the preamp output (as labeled on the schematic) directly into the effects return. As long as I am not overlooking anything, this should work. but the question is... am I overlooking something?
Question 2: because I am using only the preamp, what kind of power transformer should I use? I shouldn't need to use the 100 watt twin PT because I don't have to drive 100 watts of power tubes. I want to probably use a toroidal transformer or a transformer that mounts directly inside the 19 inch rack.

The idea here is that most power amp stages are similar, but this is the part of the amp that costs the most. I am trying to get the most tone flexibility out of the least amount of money that I am having to spend on 100 watt output and power transformers. The goal is to patch them using just plain guitar speaker/patch cables. again, from my research this should work, but I am a pretty young and novice amp builder and am not completely sure if this will work (there has to be some reason nobody's done this before)
Please let me know what you guys think.

[wpaulvogel]

You’re only using 2 preamp tubes. You need to be able to supply about 20mA and that’s way overboard. A Hammond 270x would have the capability easily. I don’t know the voltage of the preamp of the Dumbleland.

[matoni]

Thanks so much for your reply.
The schematic says 400v before the rectifier if I am reading it right. Also, does anyone know the value of these resistors in the power stage? I have no clue what value resistors I should be using. I would assume it is the same (or similar) to SSS#002, which says 1.8K and 4.7K, but I would love to get the opinion of someone who knows the circuit a little better than me.

[wpaulvogel]

The amp uses 6550 tubes with high voltage but the preamp voltage is lower. The resistor values mean nothing to you until you pick a transformer and a preamp voltage. You’ll set the preamp voltage with the dropping resistors and filters in the power supply. You start with the prediction of the preamp voltage and choose the resistor values.

[matoni]

I have no clue what the preamp tubes are supposed to be running at, but I think I am going to use a Hammond 269EX power transformer.

[martin manning]

This is much more than you need. I would take wpaulvogel's suggestion and use Hammond 270X. It has a 5V rectifier winding that you could use as a relay supply. It's a bit large, at 2.625" high and about the same across the bells. You would need a 2u rack box. 261C6 would work if you are not going to use relays. A well-filtered supply of about 320V would be fine for your purpose.

[matoni]

Thanks for the input. I think I will go with that type of transformer. I was already going to use a 2U box just to give me a bit more vertical room. Thanks again for the help.