did you match the impedance? that can pop a tube if it doesn't fry the output transformer first.... no mismatchy. These thigns have external bais adjusts, did you check the bias? GC doesn't exactly look after their gear nor do most bassist come to think of it. Hell it may have the factory tubes, power tubes last a year of ahrd gigging and short out 9what happened to yours) except JJs which tend to go and go but sound like ass after a year.

did the tubes look fresh? or was the labelling paint all faded out with giant metallic burn marks allover the glass? how'd the getters look? you have to apy attention to this stuff, these aren't 1000 watt boomboxes like solid state. Its high voltage shit, not low voltage high current.

I've always found it ironic that anti tube amp guys usually have trouble with their tubes right away when they get their first tube amp... it seems to happen so consistently that I have to think some of it is user error because I've literally never had any of my amplifiers drop dead unless they needed service and I gigged them anyway.

and I told you it was too much amp for you.... tube amps are rated for extremely low THD, so before any audible overdrive or compression the amp is probably hitting 300 or damn close to it and it will just keep getting louder as its distortion is dynamic with some headroom and lots of bandwidth versus trsnsistors which are a fuzzy brick wall. The peak voltage swing on an SVT is insanely high. You would need 2 or 3 1000 watt ahrtkes to equal it.

rule fo thumb though, buy used amp at GC? buy new tubes while you're there.... in fact, insist they throw the tubes in at cost. And make sure you rebias her right after you change them.

Imagie this as a roadster or sports car.... tis powerfula dn way better and more fun than a Honda civic but you have tot ake care of it if you want it to perform properly and not break down.... a solid state amp is a civic. its a good reliable ride but its not exactly fun and it ain't terribly powerful. Even if you tweak it out Vin Diesel style like fast n the furious its still just a civic and the vintage Shelby cobra that's been maintiained will eat it alive.

When I bought it, GC took it to the back for maintenance and cleaning. They said they biased it. I plan on buying a JJ soon and doing it myself soon. The most Ampeg guy I know of swears buy them. He refuses to pay 4x the price for the new OS or whatever they are called.

I'll bet they just took it in the back and jerked off to porn for 20 minutes. NI don't trust GC, their techs are unqualified usually and are sneaky as fuck.

New old stock.... don't bother, half the time the shit is forged and not well matched because old 6550s and KT88s are dwindling. JJs are the most reliable current production tube and in the case of your tube type they sound very good. You may want to try KT88s, the UK equivalent of the 6550. Its basically the same tube but the KT stands for Kinkless Tetrode. Most Tetrode power tubes have a midrange 'kink' that's like a notch filter dipping a specific frequency band in the output section, but the UK Kinkless Tetrodes don't have this and sound thicker. They are also a more robust physical design that holds up to physical vibration and extreme temperature changes better when the amps being carted around.

That said, I am reiterating what I said about ampeg tube heads last year, the SVT may be too much amp for you and you may be better off with the 100+ watt V4B. Same preamp pretty much, different, smaller power amp. loud as all fck, but you'll be able tog et the output section to compress and add some color before you drown out the band. And the tube set is a quarter or less of the cos of the ampeg tube set.

Something I liked about this amp was that once I dialed it in, it was the raw sound of my bass. I couldn't perceive any color. It was nice just hearing what I hear when I play it unplugged at high volume. Same growl.

yeah its a pretty hifi design tube, the old suns and hiwatts are even moreso hifi ... solid ampeg alternatives but they're 100 watts less for the big bass models so you see less of them on the big stages these days... its funny because the amp is actually adding a lot, or rather its amplifying thigns that are abrely there at the pickup, more harmonics (and the musical ones I might add) than a solid state device would, even more than hybrid amps.... thing is, when you play electric solidbodies unplugged your ear gets an inordinate amount of harmonics just because of the way your ear ehars and the way the sound bounces off the body but that's not what the pickup ehars. There's a psychoacoustic thing with your perception of the tube's non-linear response sounding like your unplugged basses. But that doesn't mean solid state is more right or whatever because it gives you mostly what the pickup hears. If what you hear in your head is a big loud, deep version of your unplugged tone? then that's right and if an ampeg does that with minimal control futzing then I guess the ampeg is right. or that's my take.

you may find this to be interesting.... I;ve ehard of the 400PS from fender but I never realized it was 475, not just 400 watts and I enver knew it could pass 40 hertz, I figured it sloped off like the SVT (there are electronic reasons for the HPF, low parasitic oscilaltions etc, but I guess the layout of the PS avoids those pitfalls through parts placement)... anyway, here, the monster truck of bass amps:

https://reverb.com/news/the-most-powerful-tube-amp-of-all-time-behind-the-fender-400-ps

I hate SVT's even though I don't play bass, they look so ugly.

I don't think most soundmen in venues less than 500 capacity would put their hands down on this 300 watt behemoth, but they do sound good and cut quite a figure atop their fridge-sized 8x10 cabs :-)