I think a decent PA could suffice. I personally would opt for 3 way speakers with 12" or larger woofers, to retain bass response. I would also acquire a decent subwoofer for low frequency reinforcement. Even good-quality 15" woofer 3-ways can't produce the punch of a quality tuned sub. Look into 4th order bandpass stuff.
Go ahead and try replacing those 1N4448 diodes with 1N914. Should be no problem. You could try different combinations as well, even LEDs.
As far as the tank goes, I didn't find any information about the 1BB2E4A tank. You should keep the input and output impedances relatively the same as the original, if you were to try a different tank. That being said, I don't think using a tank that has different impedances would ruin anything, since we're talking about very low power signals. You may get oscillation, or unwanted effects, though.
You could also play with filtering the tank circuit. You said that the treble is a bit too much for you, so an easy thing to try would be to connect a .001uF or so capacitor across the tank input (across signal and ground) to attenuate some of that treble. A higher value will attenuate lower frequencies, and a lower value will attenuate higher frequencies.
Did the DVD player already have video inputs? If not, don't even bother, you wouldn't be able to accomplish your goal without serious help. If so, it's a matter of soldering connections and mounting connectors.
Geeze, you guys, do some calculations. In his circuit, the 47K and 100K are current limiters. With them connected in parallel, with the pot dialed to 0 ohms (worst case), the maximum power dissipation would be 2.5mW. That's 9 volts divided by 31972 ohms (resistors in parallel) which is 281 micro amps, times 9 volts is 2.5mW. Not exactly pushing it. The diodes won't be conducting all the time, so actual values will be less than that.
The configuration he shows is a standard clipping circuit that will produce fuzz and more distortion-like tones. For a more overdrive sound, the clipping diodes should be connected in the feedback loop of the op amp (where the boost switch is.)
And props to metal-guy for experimenting! Never stop experimenting... the worst you could do is end existence as we know it, which might turn out to be a good thing
You may get a bit of induction. You might want to use coax instead of single conductor for those connections. Otherwise, not too bad for your first build. Maybe work on lead dress. The soldering looks good. I didn't have a problem with the first pictures.
Tough problem. If the guitar amps that you want to use have powered outputs, try connecting your stereo speakers to them, and plug the mics into the clean channels of the amps. Otherwise, yeah, you'll need to hook into the house PA if they have one.
You could also go with the Tung-Sol 12AX7. It seems to have good reviews. I don't think spending a bunch of cash on a Black Sable or Telefunken is worth it for a guitar amp. I prefer JJ over EH, but that's just me. For the price, I'd go with the Mullard.
Sounds like a killer project. Should be loads of fun! I think triode mode sounds like ass, though. Just my opinion. Always go with ceramic sockets. I definitely agree with reverb on both channels. Not having a normal with reverb capability is just silly. I've been liking the new Mullard tubes lately. As for the 6v6... how about Philips NOS? http://www.tubedepot.com/nos-6v6gt-jan.html
Can't you just turn the amp modeling off? All it's doing is processing the signal to sound like it's running through another amp. With it off, you should have only the other effects affecting the signal.
If that sounds cool to you, connect the output to IC2B (upper right-hand corner of first schematic page, where it says "MASTER") like I suggested.
Edit: Sorry, should have looked at it more closely. You might be able to remove it by removing the amp type pot completely from the circuit.
1. For the tone control? A wire would attenuate all of the signal, not just the higher frequencies. A resistor would attenuate most of the lower frequencies, depending on the resistance.
2. I don't know. Best sounding is rather subjective.
3. Noise reduction. In order to ground it to the body, the body would have to be conductive, i.e. made of metal, or covered with conductive paint. Depending on the bridge plating or coating, you might be able to get solder to stick to it.
^ It might work. Or, you could isolate the effects part of the circuitry, and connect to that. Looking at the schematic http://www.westebbe.com/Vox/AD15_30Servicemanual.pdf, the easiest would probably be to connect your guitar to the standard input, and take the signal coming off pin 7 of IC2B, and run that into your amp. Unplug CN3, which goes to the power section.
Inverting buffers are basically just inverting comparators, not amplifiers. Amplifiers are meant to copy and amplify a signal, regardless of voltage, within its limits. A comparator's output switches quickly from high to low, or low to high, depending on the input voltage. The input voltage is compared to a set threshold. With an inverter, if the threshold is exceeded, the device sinks the output, implementing a low. If the input is below the threshold, the output sources, or is high. The analog aspect of the circuitry is retained because it takes time for the output to switch, usually tens of nanoseconds.
What do you mean, "out of phase"? That circuit you posted should work for what you want to do, I would think. The buffers are only used to create an oscillator, and won't affect the "tone" of your signal, just the amplitude.
The light bulb or light source should be used to isolate the input from the rest of the circuit. The bulb's intensity fluctuates according to the input intensity. You could use an LED if you connect a resistor in series with it between the anode and the bridge rectifier +. A 1K resistor probably will be fine.
Each one of those chips is socketed, meaning you could pop them out, and replace with new very easily. I would start by replacing all the chips. Make sure you insert them the right way. There's almost always a divet and/or a circle at one end only. If that doesn't fix it, you'll require a technician to help you.