Here's something from today's e-mail. Someone asked me about the Fender '94-'01 "Twin-Amp" and most of what I said applies to this discussion. A 100WRMS tube guitar head is excessive for the reasons that have already been mentioned, but a 100WRMS open-back tube combo amp is idiotic in the 2003 context. Its main function at high volumes is to beat the tubes and circuitry to death with percussive vibration.
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> Do you own one?
Yeah. A brand-new 2001 I bought for $599.99 when they were closed out. It sits in the studio under a mover's quilt, where the cat sleeps on it.
> any opinions?
It's a decent enough amp, but too heavy, too loud, too fragile a case for the weight (of the five others I've seen, four had broken cases) and at the end of the day, I think it's pretty clear for technical reasons that a 100WRMS open-back tube combo is both a flawed and obsolete concept. At those wattages, you really need a separate head and a real enclosure - and that's assuming a 100WRMS tube guitar amp even makes any sense in the first place.
> How about reliability?
I can't address this from personal experience, as I've never used mine except around the house at bedroom volumes. It's a complex tube amp and that eventually translates to problems, especially if it's used at anywhere near its rated output. There are also the usual Fender bad solder joints that will eventually show up, particularly if subjected to the vibration battering the amp will get at the volumes it was designed to produce. There's a current thread on problems one user is having with this amp on alt.guitar.amps on UseNet.
> How about tube upgrades?
I think this is probably not worth the effort if the tubes in it are good, and the fact that it's a high-wattage, high-volume combo will reduce your practical options for the 12AX7 and 12AT7 tubes to short-plates anyway due to the vibration issue. JJs are probably the best bet. The stock Fender Sovtek so-called 5881s are not great sounding power tubes, but they are serviceable. I've come to the conclusion that the tube-substitution game is largely overrated in its effect on an amp without pre-existing tube problems. There's a large element of self-delusion in most claims for greatly improved sound after "upgrades" on most amps.
If I don't sound enthusiastic about this amp, it's because I'm not. I got it because it was a steal and back in the old days before onstage sound reinforcement, the Twin series was the pro setup and I never had one then. I bought it because I wanted one thirty-five years ago, not because it made the least bit of sense in the 21st century.
You'll get different opinions on the board, but they won't be as objective as the info above. People are all hot for these amps until they actually own one. Most people I've known who got them dumped them after the novelty wore off.