Super Reverb with 2 12 in 8 ohm speakers

[Doc Stitches]

I want to run 2 1973 Fender 8 ohm speakers in my 1973 SR which I have changed to AB763....see photos

What are my options ?

The PT codes : K022798, 606 0973, OSA 827 It sounds great with no obvious issues but I was just reminded ( duh )

this could damage the amp. I like the sounds with the 2 12s and I have the chassis in a smaller cab ( lighter )...HELP...



Doc

[stereomonostereo]

You could run them at 4 ohms with no problems. The OT i believe is 2 ohms, but going 2 ohms in that direction won't hurt

[Doc Stitches]

Thanks stereomonostereo

So it's OK the way it is ?

Doc

[stereomonostereo]

Yep. You never want to go in the other direction, ie. running a 4 ohm load on an 8 ohm output transformer, but going 2 to 4 isn't a problem. You'll lose some effeciency, but that's about it.

[JoeM]

Yep. You never want to go in the other direction, ie. running a 4 ohm load on an 8 ohm output transformer, but going 2 to 4 isn't a problem. You'll lose some effeciency, but that's about it.

I would think it's easier to go lower than higher (within reason)

[Chuck H]

Yup. Tube amps seem to be safer into a short than too high a load. There was a post here some time back where a guy ran his Bassman head as a preamp. That is, he plugged a cord into the "ext speaker" jack and used signal from that to drive another amp. Of course this means the output is shorted by the unused main speaker jack. But I guess there was enough bleed signal to make it work. He mentioned that he'd been doing it for a couple of years!!!

I've never had any trouble mismatching 2x or -2x impedance with any tube amp.

[olddawg]

I've always wondered about Super Reverbs. They are set up for a 2 ohm load and have an external speaker jack. So.... if you used a balanced cab it would be a 2 ohm extension cab. It would be a 1 ohm load. I'm sure it's fine because it was designed that way. It just sounds a little odd. There are .47 ohm speakers out there too.

[g1]

Not just Super's but pretty much any older Fender amp. Impedance is matched with internal speaker only. Once you plug another cab into the Ext. spkr. jack, you are running into a lower impedance load.

[stereomonostereo]

I've always understood it like a funnel. For example, if you had a 16 ohm output transformer, and were dumping it down into a 4 ohm speaker, it would 'strangle' the signal and overheat the OT.

[hasserl]

I've always understood it like a funnel. For example, if you had a 16 ohm output transformer, and were dumping it down into a 4 ohm speaker, it would 'strangle' the signal and overheat the OT.

Certainly there is a risk of elevated current flow resulting in an overheated output transformer, if the OT is marginal to begin with. But of more concern is elevated flyback voltage that can result from increased impedance speaker load causing damage to the OT by piercing thru the winding insulation and arcing, causing a short in the windings. Also a concern from the high flyback voltage is arcing at the tube sockets; and then there is the danger of increased screen current causing failure of the screen grid resistors (if equipped). Overall a reduced impedance load offers less stress to the amp components than an increased impedance load. Most amps seem to do fine with a slight mismatch like -50% to +100%, but that is not universal, some don't tolerate a mismatch well at all.