• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Simple question: Stereo to monos. How.

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OK, you are building 2 chassis and a PSU on each. Obviously, you can't share a single 12AT7 between channels. You need a "bottle" in each monoblock. There are 2 ways to go about this. Use 12AT7s and wire up system 1 in an amp and system 2 in the 2nd amp. When the drivers wear out, exchange the bottles between the 2 amps and double the service life. The other solution to the separate driver problem is to build with 6AB4s. The 6AB4 is a 7 pin mini single triode, which is electrically equivalent to each of the pair of triodes in a 12AT7.

Oh yeah, each PSU has to produce the voltage shown, but only 1/2 the current.
 
Put in a 5Y3 instead of a 5U4. You will save 5 Watts of heat.

6AB4s are much harder to find than 12AT7s. Also, if you do the trick with the 12AT7s you can only wire up the appropriate half of the heater and save a little more heat, as well as tube life. Of course those tubes hardly ever wear out; the 6BQ5s will go first.
 
Depending on the current capability of your power transformer(s), the R and C values in the power supply will probably need adjusting since you will be pulling 1/2 of the current in each supply. PSUDII is your friend here.
 
In general, the higher voltage isn't likely to cause a problem. Yet, it's something to consider and, if necessary, make correction.

A smaller transformer and choke would also be a good idea, save a little energy and weight and cost. You'll probably see no more than 330V anyway.
 
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