Ampeg SVT VR to 8Ω cabinet

Yes it will work normally, that is, it will produce less output power, overheat the output tubes and accelerate their failure due to over voltage, it will also test the insulation of the primary windings in the output transformer every time you abuse your amp by running it into twice the nominal output impedance it was designed for.
However this equipment was originally designed to be operated by idiots and therefore has a great deal of Inherant redundancy built in.
There are idiots who have operated Ampeg SVT tube amplifiers for long periods of time at the wrong load without costing them selves an output transformer.

 

Um...well...

You're a talented dude who knows his stuff, but Bill Hughes is on record here saying that SVT's are absolutely fine with a 2:1 output transformer mismatch because they've overbuilt, even if you crank them hard. Since he invented it, it's pretty hard to dispute, and since I've done it before with rentals (and accidentally with my Heritage SVT-CL because I didn't understand how these new-fangled 810's plug up at first), I believe it. Jess Oliver (RIP) is also on record saying that a 2:1 mismatch in either direction in a tube amp is fine because impedance is ever changing as you play anyway, and as long as it never sees infinite ohms (no load at all) it's fine. He would sometimes install 4 ohm speakers in customers' B-15's when they were looking for extra tightness. To my knowledge, it hasn't caused a B-15 failure yet.

Personally, I don't care for the sound of tube amps being run at a 2:1 mismatch because it tightens and compresses them a little too much for my tastes, but while in theory your statement was correct, it doesn't seem to quite play out that way in real life, and if Bill says it's OK, then I believe it's OK.

EDIT: I just saw Hodgy liked your post. Would be very interested to get your take on this as an Ampeg expert, Hodgy.

 

Dino addressed Ampeg's policy in an AmpegTV video. They say to match the amp and cabinet's impedance.

It is true that a mismatch will affect how the amp sounds and I also prefer it matched.

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Should also mention that a mismatch will void your warranty if something happens as a result of the mismatch.

 

All that being said, people do use the VR with 8 ohm cabs. As was mentioned, there is no free lunch.

 

I remember watching Later With Jools a few years ago andi lost count if how many times I saw a SVT-VR/CL on top of a 8 ohm Ampeg 410HE cab.

 

The designers say it's OK.
The factory won't warranty below the minimum load.
Bassmec stated the above and explained why; imagine the first reply was the most complete!
Well done mate.

 

Bottom line, if you care about your gear, run it as it was designed. In this case, either a 4 or 2 ohm load. Period.

 

judging by how many people want to do this (or do it unknowingly), vs how many ever run one SVT head into two 8x10 cabs anymore, i gotta think there would be a pretty good argument for an OT redesign that would let the amp properly do 8Ω and 4Ω, rather than the current 4Ω and 2Ω.

and just recently i did a gig where our bass player used his '90s classic on an 8Ω cab; about halfway through the night the amp went belly-up! after some quick power-cycling and "percussive maintenance" on my part it came back up and we finished the show, but the lesson was learned and we ain't doin' that again

 

Ya, it's definitely one of those "Not with MY SVT!" things for me, but I'll do it with a rental. Hey, if they bring it like that, not my fault if it poops the bed. Hasn't yet, though I can't say I put a lot of demand on them, either.

But you bring up a good topic, Walter...what would be needed to make the SVT run at 2-4-8? Certainly it can't be as easy as adding a tap to the output tranny, right?

 

Sounds like Bassmec'd been saving that rant for some time.

 

you sure that 410HE on Jools wasnt a HLF? thats 4 ohm

 

Output transformer replacement is expensive.

 

99% sure. I've watched it plenty and tried to see rear or side angle shots. Straight back... No towel bar.
Also the HLF is taller.
Of course the cabs used could have been modifies to be 4 or 2 ohms. I know not.