Ampeg SVT Classic

[lowell]

This amp has the 2 bias pots and green/red leds on the back panel. I'm pretty sure it's not too important to use matched tubes in these amps because each half of the p-p OT has its own bias adjust. Just a thought. Someone please chime in if this isn't right. Fyi I just retubed one with 2 sets of matched trios (trios?) and it seems fine!

[kg]

sounds good to me.

imo and ime matched power tubes for MI amps are a ripoff.

[lowell]

I mostly agree!

[Ronsonic]

One of the things you'll notice is that with matched tubes you'll have a pretty generous range on the pots between when the greens turn on and when it goes red. With poorly matched tubes that window of adjustment gets smaller and the adjustment gets fidgety.

I'll agree that for most amps tube matching is more of an "advertizable feature" than a technical matter. It don't hurt, but doesn't pay to get too fussy.

A couple of reasons I do order matched sets, is the matching process comes with a burn in. Depending on your vendor that could be anywhere from 24 to 100 hours. Does cut the infant mortality rate. Another reason is that matched sets tend to come from the fat part of the bell curve. Imagine yourself a tube seller and you get in a pile of tubes. You'll want to sort them to spec on the shelf, the stack that gets deep gets packed as sets. The lonely guys on the end go out to the people who didn't want matches. Some sellers don't do that and when you order unmatched tubes you get tubes they haven't tested to spec. Others, well, it's sorta less honest, but it isn't a lie either.

[kg]

who says the middle of the spec curve tubes sound the best?

[Ronsonic]

To sound best it must continue to make sound. Reliability lives in the boring part of the bell curve. Or that's what the young lady lamented after years of dating.

[kg]

oh, so you like solid state then?







(ps.. i'm just kiddin around ron)

[Gtr_tech]

I use matched sets for 1 reason only......they bias up real close. I don't want one idling at 11w and the other at 21w....

[lowell]

That is a very good reason to use matched sets. One way to avoid this and stick it to tube retailers (obviously) would be to design all amps with individual bias adjustment for each tube.

[Gtr_tech]

Thats been done before (Sound City?) but never really caught on. In all reality, unless you a tube importer, its harder to find onesey-twosey unmatched tubes than it is matched pairs and quads. So it just makes more sense to get them matched not only for bias point, but Gm as well.

And....multiple bias adjusts will complicate tube replacement for the "shadetree" amp tinkerer who likes to replace his own tubes.

[kg]

I use matched sets for 1 reason only......they bias up real close. I don't want one idling at 11w and the other at 21w....

i match idle currents side to side and call it done.

if one tube of a parallel set is a miniature pony and the other a clydesdale, so be it. they'll all end up matched when they die.