Good point. Still, some of the reissues sound exactly like they had shown, and also the way Bill Hughes had alluded too.
I remember the first time I ever fired up an SVT. I had just bought it with the money that I had saved to buy an engagement ring for a girl who said yes and then bolted. She did me a huge favor.
I'm sure you are aware that the 400+ is fixed bias. This is why Mesa wants you to by their tubes. Not saying that the bias couldn't be adjusted, but not easily.
It's nowhere near as difficult as you might think. Matter of fact, installing a variable adjustable bias control isn't even that big of a deal. Mesa does more than its own share of BS marketing,
especially concerning tubes. When bias cannot be adjusted for aging, then tubes have to replaced any time they age outside of the bias voltage setting which makes them appear to be losing power and dying, when in fact, it's just a perfectly normal part of their operation. Typically after around a hundred or so hours of hard use, power tubes will need their bias reduced to maintain their rated output power. It's not because they're inferior; their cathodes have simply used more of the electrons deposited on the surface of the cathode and it takes a slightly higher voltage to energize the interior of the tungsten material of the cathode. Transistors do it too, but for different reasons, and since their operational voltages are orders of magnitude smaller than tubes', the loss of performance is much less noticeable.
The guy I bought it from runs an amp repair shop (Dave's Sound Repair in Whippany, N.J.). He's a good guy and generally knows what he's doing. I guess at the time the amp had Groove Tubes, and he hates Groove Tubes. He also installed some kind of protection circuit on the power tube grids. They have fuses and LEDs to let you know if you blew a fuse.
Screen grid fuses usually are there to prevent runaway from oscillation caused by a number of things. 400+'s don't run voltages high enough to justify such a measure, not to mention that 6L6GC's are generally not prone to screen oscillation anyway. If the amp ran at higher voltages and used EL34's, whose internal geometry and higher plate resistance makes oscillation more likely, I could see doing that (though I wouldn't.) It will help to keep the amp going in case of misuse (improper output loads, etc) but it would compromise the sound of the amp, limit its output power below rating, and could cause a bunch of other problems.
Groove Tubes never made their own tubes anyway, though they often implied or outright lied otherwise, nor were their ratings any real kind of operational parameter. They just bought various tubes wholesale, ran bias tests on them, and grouped simlilarly biasing tubes together. They also had a good algorithm which could predict how the tubes would age based on their cathode properties and grouped together tubes that they purposefully knew would become grossly mistmatched as they aged, typically right as their six month warranty expired.
Different tubes do sound different however.
That's a major understatement. Even among the same type, different makes and variations can have enormous variations in performance.
The amp needs a little servicing. Two pots got broken off (which they didn't use nylon shafts!), and then shortly after that it started blowing it's main fuse, so I stopped using it until I could get it looked at, and then just never got around to it. But now I want to start using it again.
Depending on which pots broke, that might be the problem, but not necessarily. You don't want nylon shafts for most amps anyway. If a pot breaks, it's better to short potentially dangerous voltage to the chassis case/ ground lug of the power cord.
