Downunderwonder

Nice looking plywood.

Fairly 'reliable' at around about 2/3 of the total nominal impedance rating for a driver in a cab. If you measure DCR, the driver impedance in cab is going to be the next rounded off common figure on the larger side of your DCR. Eg, DCR is 5.8ohm, '8 ohm' driver. I don't know how well that works for OP's PA cabs with crossovers and compression drivers hooked up.

I'd be surprised if it isn't a 12ax7 / ECC83, but it will be printed on the circuit board for good measure.

''Engineering Sample'' = mates rates on the 'prototype' materials? Bloody good show.

Lots of jibberjabber about strength. Stiffness is as much related to shape, as the strength of the material.

Only enough watts to keep you happy without straining the 15.

Everything Subway since he was hired at Mesa. Before that Mesa were apparently quite ok with a bit of a mismatching response between cabs of a line. One cab even had an abysmal mismatch of 410 and 115 in the same box.

This man's advice is never to be ignored.

When I properly biamped my 115 and 210 there was a distinct improvement in the clarity of my tone. Powering them from one amp still sounded ok so that is what I proceeded to do. Carrying all the biamping gear was too much work. The improved tone indicates that the maths is correct. My spine is also correct.

Don't forget all the analog distortions and chorus pedals that invert the signal along the way. Blending those back with a clean signal can less than intelligible.

The problem with parallel blends is the phase of the signal in one chain can end up out of whack with the clean(er) channel. You wind up sounding like muppet on stage with a giant bass rig competing with the PA.

I think you might be exaggerating a little. I got my Trace rig in 96 when I was on $20 an hour. That would have been roughly double the minimum wage back then. Iirc I paid around 3k for 250w SMX and 1518 cab = 300 hours at min wage. (Forgot about ''youth rates'' back in the day. Would've been about $5 an hour so 600 hours. Ouch. No kids buying Trace amps.) It worked for rock in bars but we had to have the guitarist with the 50w Marshall stack to pull his head in.

You got it a police auction after they recovered it in a gang house raid after they had burgled a studio that had it as a spare on the shelf and never wrote down the serial number.

I couldn't tell you how many buttons I ripped off shirts by clutching my 1518 Trace cab to my chest and snagging the button in the button snagging grill.

So long as the impedance is ok for your amp and it makes nice bass noises it doesn't much matter what the power rating is on the driver. It will tell you when it's getting too much power by failing to get any louder as you turn it up. Turn it back down from there a squirt or it will fry. If it's making nasty flappy noises you have too much low end in your signal. Turn down the bass EQ and or volume.

You mean wRAPPERS.

Are those front 'vents' not part of the front panel? Those would be wider than 19'' and not removable I think.

It's only underpowered for those who need crushing volume. The people that buy them seem by and large to be quite happy with them.

You asked what was possible with a driver upgrade. The answer is a shift in tonality with next to no extra volume in the bottom end. Kicking these kinds of cans around you get to know when a plan has a chance and when it's trying to break the rules. The rules can't be broken. No amount of complaints can change that.

Padded backpack.

Depends on the model of Trace. There's lots of different schemes of combos! 17'' racks? Don't think so. 19'' is the standard. Makes me think you have one of the AH series stuffed into a combo? If so there could well be nuts in place at the sides and a lid already? Then you would need custom ears and a 19'' rack case.

DIY. Two slabs of ply for shelves. Another slab of ply cut across at an angle makes two feet. They don't have to be exact mirror images. Flip one over and align the top and bottom. The closer you got to exactly cutting mirrored pieces the closer the ends will match. Trim the ends. Now cut in the lower shelf rests parallel to the bottom. Now you have an angled top shelf with heaps of room under for power supply. By having it at an angle and the bottom one flat you get an extremely rigid structure with 4 screws each side.

Vintage Trace amps can pump a sine at their rated output without overheating. That's the old way of rating. When it comes to slamming a low bass note that happens with a very satisfying transient burst. Hence the legendary "Trace Watts''.

It would be interesting to see if the extra couple of litres made any difference. As I read it, the OP being happy with the low mid bumped tone he has, the green curve would make him really unimpressed trading 4dB down in low mids for a 2dB bump up down lower.