The company that built and sold this record player was probably either inspired by Muntz TV or it perhaps was Muntz immediate predecessor. Certainly the "design philosophy" is similar: make it as simple as possible with no redundant parts.
Read an opinion about this from (deceased) analog guru Robert Pease.
1. I've replaced the original Selenium Rectifier with a diode and I'm just now noticing that the plus and minus on either side of the diode symbol are backwards. Is there something to this, or is it inconsequential?
Ignore the plus and minus symbols. What is important is the symbol, usually a line of contrasting color around one end of the diode, that represents the cathode of the diode. The cathode provides a rectified positive DC output with respect to common when an AC voltage with respect to common is applied to the anode.
Be careful replacing selenium rectifiers with modern silicon diode rectifiers because the forward voltage drops are quite different... about 0.7 V for silicon diodes and several volts to a dozen volts or more for selenium stacks. This will cause the rectified DC voltage to be greater with silicon rectifiers than with selenium. Some folks put a resistor in series with the silicon diode to simulate the forward drop across the selenium rectifier and preserve the original power supply voltage, but the value depends on how much current is normally drawn from the DC supply. Your circuit already has a 150Ω resistor, R5, in series with diode, M1, so perhaps the Sams schematic already incorporates a silicon diode as a replacement for a selenium rectifier.
2. Is the 25VAC listed after the motor supposed to be actual voltage at that part of the circuit, or the amount of volts used up by the motor (AKA voltage drop)?
The 25 VAC after the motor is the nominal voltage across the cathode heater filaments of the 25CA5 pentode vacuum tube power amplifier. This tube has an indirectly heated cathode (pin 1 or K) internally connected to the pentode suppressor grid. The motor windings act as an inductive reactance in series with the tube heater filaments to lower the voltage supplied to those heater elements. This is a lot cheaper than a dedicated filament transformer.
3. Would I be able to remove the vacuum tube and power on the unit without damaging anything?
You
must leave the 25CA5 vacuum tube inserted in its socket, and its filament heater
must be intact and conducting current when power is applied. The voltage drop across the filament is part of the circuit for the turntable motor. You
may be able to "short out" the tube filament with a jumper wire and run the turntable motor directly from the mains 115 VAC power, but a better idea is to replace a defective tube filament with an
82Ω, 10 watt, power resistor and remove the tube from it's socket. The motor windings may not be capable of operation directly from the AC line power without overheating.
Note: In the interest of providing a low-cost solution, the manufacturer used a high-output-level crystal monophonic transducer in the tone arm of this turntable. Attempts to "play" a vinyl stereo record with this turntable will likely "plow up" the stereo track and render the record useless because of the needle style and tone arm pressure used. Should be okay for ancient "big hole" 45 rpm records though.
