VTL MB-450 "Generations"

I believe the first significant upgrade was the "Signature" version output transformers (although I'm not completely sure this basic amp actually went by the "450" designation and used 6550C's before those transformers were incorporated). In any case, taking that version (introduced around '96 I think, supposedly concurrent with a leap in build quality) as the baseline, the next significant changes, in addition to the resistor package mentioned above, also upgraded the B+ fusing to 600v ceramic types. Coupling cap upgrades may have been optional during this time. Likewise the external 'soft-start' modules, which I think became standard somewhere along the way (with a price increase), maybe at the same time the 'super-balanced' input circuit was introduced.

This last significant change might also incorporate upgraded caps as standard, but I'm not sure about that either. This version cannot be upgraded to from the previous versions, the circuit board is too different. I can't comment on Albert's info that this version may not sound as good as the previous Signature versions, but Bea has told me that the new input is not as big a sonic upgrade in her view as are the better coupling caps.

Personally, if I were in the market for these amps I would try to go with '98 production or newer (this is what my 185's are, and I think they're more nicely turned-out than the '96 example I've seen -- don't know about '97), and either stick with ones that came originally with the higher-rated fusing or were upgraded at the factory, or else be prepared to do the same if they predate this improvement (as I did). If you can find a pair with either the MultiCap or InfiniCap upgrade that's great, but if not you'll probably want to figure on upgrading these yourself (I'm planning on doing this, but not through the factory). The soft-start modules are probably very optional unless you have a chronic problem with tripping your line's circuit-breaker upon turn-on of one monoblock.

Zaikes, good additional information.

I'm pretty sure the cap upgrade path removes the MIT's and replaces them with Infinicap. Between the guys in my group and those I trade data with we have upgraded eight VTL amps and this is one of the more important things you can do sonically.

I forgot about the Signature transformer update. I have not shopped for a pair of VTL's old enough to exclude that possibility. It’s certainly an important upgrade.

I will warn those that ignore the resistor upgrade, I don't know if it applies to the 450, but the 750 can tear itself up if the old resistor package fails.

One member of my group had this happen and one or more large electrolytic capacitors failed, sounding very much like a .22 caliber hand gun as it forced the rubber safety plugs out and died. Fortunately the VTL is so well designed there was no sparks, or danger, the fuses cut all the power and no one was ever in danger.

However, the cost to make this additional repair was in excess of $1000.00. I would do enough homework to insure that safety upgrade was done if only to save yourself from future repairs.

Wow! That's what's great about A'gon, not just facts and information (which is what I was looking for) but interpretation of the information and advice about what's most important.

So along the way there was: A signature output transformer, Resistor changes, InfiniCaps, B+ Fuse change, Soft start modules, Super Balanced input circuit.

I talked to a dealer today about the newest versions to be released soon and he did mention the auto-bias circuit (which I can live without) along with the new cosmetics (that I happen to like).

I will drop Bea a line to see if she can put the upgrades together with a serial number.

Thanks Albert & Zaikesman for your informative posts, it's exactly the info I was looking for.

I agree that the new faceplate design, assuming it's similar to the new ST-150S, certainly looks nice with the glass and curved lines, but personally I wouldn't trade the utilitarian handles of the old faceplate -- these amps are heavy. What I didn't realize is that (provided your dealer is correct) the newest versions of the Signature amps will automatically adjust bias...

Albert wrote: "I'm pretty sure the cap upgrade path removes the MIT's and replaces them with Infinicaps." The Sig amps like mine, with no cap upgrades, had VTL-branded caps, made I believe by Reliable but not as premium as their Multi's or MIT's. This can be confusing, because there are several different kinds/grades of MultiCaps, and VTL never specified which one they used, claiming they were proprietary. They do the same thing now with their TRT InfiniCaps. It's something I asked Peter Moncrieff at TRT about, but he didn't or wouldn't answer on that topic. I wound up buying his DynamiCaps instead anyway, which he indicates have a slightly more euphonically tailored sound, whereas the Infini's are supposed to be more "direct". I sort of made my choice based on complementing the swap to my preferred EH KT88 output tubes, and also Michael Percy's advice.

So - if needed - what kind of a job is it to replace the caps? I'm decent with a soldering iron but I've mostly upgraded old tube guitar amps, not something with this level of build quality. I had thought of rolling to KT88's on next tube swap myself, what kinds of changes do you hear?

I agree handles are nice but I would give them up for that faceplate (just have to get help putting them in place!) It also sounds like the auto-bias will come at a cost. Thanks for the details on the caps. -Bruce