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Yip. With modern preamp output impedances bandwidth issues are moot but you are adding more noise and distortion

With an input sensitivity of 0.5V for your power amp you dont really need a preamp - well certainly not a preamp with a lot of gain - fortunately most modern preamps have low gain. Too much gain and you will only be able to use a small portion of the volume knobs rotation.

Measure all the 0.22R resistors and check they are all roughly 0.22R both channels do this with amp off and cold.. Then with amplifier on AND warmed up - play music as loud as possible for at least 20 minutes - the measure voltage on the good and bad channels across their respective resistors -...

Apologies according to the manual you should adjust for 5mV across R641 and R642

If you have a multimeter you could measure the voltage from ground to each end of R633 - they should be +0.55 & -0.55V - see the schematic.

If the hum changed when you touched the chassis its probably an earthing issue in that channel. If service manual says bias should be set for 5mV they usually mean as measured across the output transistors‘ emitter resistors (each output transistor has its own emitter resistor) not speaker...

Selecting “PC” as the input name on a Samsung TV should make that input scale correctly to a computer - works on my ancient Series 5 thats been doing monitor duty for the past 10 years

Correct but that then entirely shuts down parts-rolling -and all of subjective audiophillia :) NE5532 is a BJT opamp so trying other BJT opamps should be safe. LM4562 is considered the "higher performance" NE5532 and it is, but NE5532 is very high performance anyways

32W = (12V x1A) + (5V x 3A) + (5V x1A) this is the power drawn by the devices which the OP stated. The bottom line with any UPS/battery system is the more power it can “hold” the longer it will last. Calculations will never be accurate due to battery age/condition, SOC, inverter/regulator...

Power draw is ~32W, battery is ~48W/h ….I get ~1.5 hours usage. Am I correct?

What inverters are on this list? Alternatively where is this list available?

The relays only function is to protect the power amplifier from large start up voltages - at startup the relay connects the output signal to earth, once the delay period has ended the relay opens and effectively is not connected to the output at all. So you don't need a "good" relay here any...

you use a lot of resistors in your design so just build away - if your voltages end up different you can easily increase or decrease resistor values to compensate

Cap-coupled valve preamplifiers need circuits like this because at startup you get a very large voltage at the output as the coupling caps charge up. This can easily destroy whatever the preamp is connected to (in my case it was a rather expensive sound card). The transistors are probably...

Correct. 2x 18VAC transformer with LM317/337 regulators would be better - will cost less than R1000 for parts

Ticking slowly could be oscillation usually through parasitics or ?motorboating?. Check your wiring and layout, signal in this case, would be fed back via wires or components being too close or through power supply sharing/interaction try different size filter capacitors or different earth routing.

How does it sound?

Thats quite a steep load for a 12AU7 so it wont be performing at its best. 12AU7 has an rp of ~10k so you want at least 20k on the anode - also this a voltage gain stage it so it does not need tons of current (to drive 1Meg and less than 10pf of capacitance) rather swap the excess current for...

The only caps in the circuit should be on the follower: 10uF and 0.1uF. You should direct couple the 12AU7 to the follower - get 135V on the plate of the paralleled 12AU7. For a paralleled pair of 12AU7s i get approx 11k on the anodes (or 22k on each anode) and approx 470 on cathodes (220 per...