Ampeg SVT 2-PRO @ 8 Ohms?

NKBassman · #1 10-26-2010, 11:27 AM

Recently picked up an Ampeg SVT 2-PRO here in the classifieds, and just wanted to ask the question...

How harmful is it to run this head at 8 ohms? The manual only talks about 4 and 2 ohm loads, but doesn't specificaly warn against running at 8. It probably won't happen very often, but it will probably happen eventually.

JimmyM · #2 10-26-2010, 11:45 AM

i've done it on a short term basis with rentals and it was fine. i'd never do it with my own stuff. it can stress out the tubes and/or transformer if you do it for any length of time or do it at a high volume.

NKBassman · #3 10-26-2010, 12:44 PM

Thanks Jimmy. It would most likely be at stage volume with PA support for no more than an hour at a time.

anderbass · #4 10-26-2010, 04:10 PM

What 8-ohm cab are you thinking about using, you might be able to rewire it to 2-ohm...

RickenBoogie · #5 10-26-2010, 04:50 PM

If it were MY amp, I wouldn't do it. The Output transformer is wound to either 2 or 4 ohms, and an 8 ohm load would put unnecessary stress on the tubes, and OT. Maybe wouldn't kill the amp, but it's kinda like smoking cigarettes, won't kill you right away, but you'll live a shorter life. Not worth the risk. (oh, and I do smoke cigs).

tekhedd · #6 10-26-2010, 04:54 PM

This is a tube amp with a transformer-coupled tube amplifier stage. Running with higher-than-rated loads you run the risk of damage. Lower impedance loads are generally fine.

In other words, don't do it.

This question seems familiar somehow.

big evil robot · #7 10-26-2010, 06:19 PM

Very unnecessary to put that 8ohm load on the tubes, see if you can borrow another 8ohm cab to split it out to 4ohms total.

NKBassman · #8 10-26-2010, 06:36 PM

Ok thanks everyone. I'll avoid it at all costs.

Grooveman1961 · #9 10-27-2010, 08:58 AM

I don't understand

Higher speaker impedance = higher reflected impedance to transformer primary = lower current= less heat/power

And this stresses the tubes and such more?

Jerrold Tiers · #10 10-28-2010, 10:43 PM

The theory is that peak voltages are higher.

And they actually are..... That "can" cause trouble, stressing insulation and parts, not to mention that tubes aren't made as well as they once were, and they can break down and arc also.....

Mostly it makes no difference if you don't hit the amp hard and play loud...... Like THAT is realistic these days.....

It's not a guaranteed "you do this and it kills your amp" deal, but it might happen.

JimmyM · #11 10-28-2010, 10:57 PM

Quote:

Originally Posted by Jerrold Tiers

Mostly it makes no difference if you don't hit the amp hard and play loud...... Like THAT is realistic these days.....

i can see you've never met bowzer. it's realistic in his band

NKBassman · #12 10-29-2010, 07:29 AM

Quote:

Originally Posted by Jerrold Tiers

Mostly it makes no difference if you don't hit the amp hard and play loud......

HAH! Yeah right. Like that'll ever happen.

Had it cranked right up at practice last night through two 410 cabs. Master volume at about 2 o'clock, bass and treble boosted, slight cut on low mids, experimented with the drive knob but ended up leaving it at around 1:00, and none of the boost switches engaged.

Sounded great! I ended up pushing the -15dB swtich though, cuz my bass was clipping the input with the gain knob at 9 o'clock.

I'm gigging with it tonight. Full report to follow.

jastacey · #13 10-29-2010, 07:45 AM

That is not a clipping lite per say, but a signal indicator, check out this thread : Ampeg SVT 2 Pro clip light problems. Please help?

NKBassman · #14 10-29-2010, 09:16 AM

Yep that's right. I have been using that method for the last year or so with my 3Pro, so I'm pretty used to adjusting the gain by ear. After I engaged the -15dB pad I had to turn the gain knob up to about noon to get the same volume as before I engaged the pad, but it just makes it that much easier to zero-in on that perfect spot. The LED was still on solid about 90% of the time, it just wasn't audibly distorting as often.