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Jaco sound on SVT classic

#21
okcrum said:
...ruining the amp in what way? There have been loads of tube amp designs over the years, using off the shelf output transformers, that are not an exact match to their normal load. In fact, the speaker itself is not a constant impedance with frequency.

IME the two things that can kill the OT are running with no load at all and arcing over the OT or output tubes, or running with too low a load impedance and overheating/shorting the OT or output tubes. Staying within a 2:1 ratio above the rated output impedance is not going to hurt anything.
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I agree that most tube amps are very forgiving to mismatched loads, but I think that overloading is more risky than under loading.
Apparently Leo Fender thought so too, since he designed his amps to dead short the outputs when there was no plug in the jacks as a safety measure.
You can't get much lower impedance than that. ;)

Freddels said:
I ran my Sunn 2000S into an 8 ohm cab for years and never had any problems. :-)
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I'm not sure if you are being humorous, but if not that's not too surprising, the 2000S was meant to run an 8 ohm cab. Unlike the SVT the 2000S has an 8 ohm tap on the output transformer.
 
#22
Tube amps don't like running at low impedances (< 8 ohms nominal) like solid state amps do easily. You won't hurt a tube amp with an 8 ohm load though. Running a tube amp into a dead short will definitely cause you problems
 
#23
I've ran my CL quite a few times with one 8ohm 4x10, but after replacing all the tubes and many other repairs, and a little research around TB, I never use it unless I am running both cabs at a 4ohm load. Seems like there was something said about it messing up the transformers? Yeah, that's the single most expensive component in the whole head.

I can get pretty close to Jaco's tone with my fretless Tobias just by rolling the neck pickup out and playing down low by the bridge. He had an epoxy coated fretboard using roundwounds, and that definitely brightened his tone up at the source.
 
#25
I always understood that with tube amps it is preferable to run a tube amp into a lower impedance speaker rather than a higher one, the opposite to transistors. FWIW I ran an SVT2 non pro from the 4 ohm out into an 8 ohm Goliath bin for a few years and then it started to play up majorly, may have been unrelated to the load issue but the tech and I always assumed it had something to do with it.
 
#27
randall p said:
Not to hijack, but running a "4 ohm" amp into a "8 ohm" speaker will do nothing. Been running my SVT CL through an 8 ohm cab for years, and no problems. Just don't run speakers BELOW the amps minimum, above is OK.
Lower impedance speakers put MORE stress on amps. Higher does not. Just don't run speakers with too LITTLE electrical resistance.
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You're wrong - with tube amps, it's potentially harmful to run above the rated impedence, and the opposite with SS amps - it's potentially harmful to run them below the rated impedence... Sure, you *might* get away with it in either instance, but if you end up having amp problems after breaking either rule, it's your own fault...



- georgestrings
 
#28
georgestrings said:
You're wrong - with tube amps, it's potentially harmful to run above the rated impedence, and the opposite with SS amps - it's potentially harmful to run them below the rated impedence... Sure, you *might* get away with it in either instance, but if you end up having amp problems after breaking either rule, it's your own fault...



- georgestrings
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That's what I recall as well. Think about it: You are strongly advised against running a tube amp without any speaker connected. The amp (or rather the power tubes) in this case would see an impedance of infinite Ohms and try to put out more power thus producing "magic smoke" after some time. (Google found this site: http://www.geofex.com/tubeampfaq/taffram.htm They explain what happens nicely.)
 
#30
georgestrings said:
You're wrong - with tube amps, it's potentially harmful to run above the rated impedence, and the opposite with SS amps - it's potentially harmful to run them below the rated impedence... Sure, you *might* get away with it in either instance, but if you end up having amp problems after breaking either rule, it's your own fault...
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Yes, it'll be my fault, even if the problems are unrelated to the output load I use. :D

Sorry, I've never had a problem doing this under less than 2:1 mismatch above rated impedance. Have you? Or are we seeing yet another TB/internet/urban legend here?

Anyway, OP, it looks like you've gotten all the useful info about sounding like Jaco that you're going to get out of this thread. :(
 
#31
dune2k said:
That's what I recall as well. Think about it: You are strongly advised against running a tube amp without any speaker connected. The amp (or rather the power tubes) in this case would see an impedance of infinite Ohms and try to put out more power thus producing "magic smoke" after some time. (Google found this site: http://www.geofex.com/tubeampfaq/taffram.htm They explain what happens nicely.)
Click to expand...

Quote from the site you cite:

Q:Will it hurt my amp/output transformer/tubes to use a mismatched speaker load?
Simple A: Within reason, no.
 

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