Running a 8ohm tube amp with a 4 ohm cab

[gibsonlp]

Hi,
I am wondering what would happen to an 8 ohm fender showman if I run it through my 4 ohm svt cab, would it damage anything in the amp?

Thanks.

[jps]

No it will not damage anything, but the tubes will run a bit hotter and may not last as long as using the correct load. This has been done forever so just plug it in and blow away the neighbors!

[antipodean]

Isn't there a chance that you'll overheat the transformer?

[jps]

Not that I know of; I ran my '66 Bandmaster into two EV B-210 cabinets with no issues.

[gibsonlp]

Thanks!

[whojamfan]

If the transformers in it have a 4 ohm tap, fitting a plug to it should fall in to a techs minimum bench charge for repairs. Then you would have 16-8-and 4 ohm output to choose from.
As was said above, it may not be a big deal, as Fender has made amps with mismatched impedences for decades without problems.

[soundmasterg]

Most amps can handle a one step mismatch either way. When you run a speaker load that is a higher load than the transformer tap, the tubes run cooler and last longer, however the sound is usually more distorted and compressed, and the amp does not make as much power as if you had the correct load. When you run a speaker load that is lower than the transformer tap, the tubes run hotter and will not last as long as a normal operation. In addition the mismatch causes a loss of power and a more distorted sound just like the other mismatch, however the distortion character is different. In both mismatches, in extreme examples (very high voltages or high power demands) you can end up with internal transformer arcing and flyback which can destroy the output transformer. As I said above though, most amps can handle a one step mismatch with no trouble. My brother ran his Silvertone 1484 through my 8 ohm cabinet for years, and the amp has a 4 ohm tap. It sounded great for leads but was too dirty for rhythm and chords, and was low on power compared to what it should be. The 1484 has a very small output transformer that is suited for a 5 watt amp, yet was being run in a 25 watt amp, and it held up just fine. I wouldn't try a mismatch in my SVT however...the voltages and power are too high to make me think it would like it very much.

Greg

[gibsonlp]

Thanks guys,
Already snagged a nice looking dual showman that appears to be all original (pics show original mid 60s transformers) so I will be running at 4 ohm after all, no need to mismatch anything.

Greg - my SVT has it's original cabs, I want to put the fender head on my 2nd 8x10 cab which runs @ 4 ohms. Once my dual showman would arrive I would have no impedance issues, yay

[jps]

Try and get both amps/cabs together for a comparison.

[johnallg]

Ric-O-Sound with a 70s SVT/2-8X10 cabs and a Fender Showman!

[gibsonlp]

Jeff - One cab is at home and one cab is in our rehearsal room with the head, they are staying there as long as my band exists, too heavy to transport (how the hell does ANYONE managed to haul such a heavy monster?)
John - One day I'll test it, I promise

[jps]

(how the hell does ANYONE managed to haul such a heavy monster?)

Kareene?

[johnallg]

Jeff - One cab is at home and one cab is in our rehearsal room with the head, they are staying there as long as my band exists, too heavy to transport (how the hell does ANYONE managed to haul such a heavy monster?)
John - One day I'll test it, I promise

Gil, and I'll probably know the time and day! Even way over here.

[gibsonlp]

Jeff - I hope that Kareene will never read this post, for your own sake
John - I'll keep it low, don't worry (yeah, right )