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Original (?) Ampeg SVT, no new tubes? Ever?

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Pyntch

Jun 28, 2011
9
0
Rochester NY
#1
I've been playing my old SVT head forever, on what I've been lead to believe is "probably 10 to 20 percent its original power" (still have never had it up past "3"), but I'm pretty sure the tubes have finally bit it.
Someone told me once that I can't get new tubes for it? Or that I'd have to replace receptacles to accommodate new tubes? This sound familiar to anyone?
Sorry for being a total noob and not offering tube/amp info, as I don't know any of it... if someone wants to tell me where to look, I'd be more than happy to supply that info.
Thanks!
 
#2
Without a doubt You can get new tubes, that'll fit without changing anything. However, with that being said, a trip to the tech to have it done wouldn't be a bad idea. For a bit of cash (bench charge, labor and parts), the tech can replace the bad tubes, rebias and fix anything else that may be going on(leaking caps or whatnot).
 
#5
Sounds to me like it's got 6146b's because he said something about converting it.

DO NOT CHANGE OUT THE 6146b's TO 6550's! 6146b's are readily available at any NOS tube store and are way cheaper than 6550's. I have a 69 SVT with 6146b's and it is awesome. Don't let any tech talk you out of keeping them.

However, you probably should have your tubes tested. Tubes aren't light bulbs, though. I've had tubes last for decades sometimes, especially old tubes from before they started making them in Russia and China. Keep the good ones and ditch the old ones. Tube amp techs always have sweet tube collections because of people demanding retubes without actually needing it. Of course, I don't have to tell you that ;)
 
#6
Hmm, would it be possible to convert a later SVT into 6146B? :D

Anyway, just listing the possibility for the OP since he doesn't seem too sure what kind he has, he's only basing his opinion on what he read here. BTW, OP, is yours a blueline or a blackline?
 
#7
Without a doubt You can get new tubes, that'll fit without changing anything. However, with that being said, a trip to the tech to have it done wouldn't be a bad idea. For a bit of cash (bench charge, labor and parts), the tech can replace the bad tubes, rebias and fix anything else that may be going on(leaking caps or whatnot).
Click to expand...

+1 YES DO THIS.
I have an original '72 Sunn (o))) model T that I was pretty sure was quieter than it should be. Took it to a tech and all the capacitors had leaked themselves almost dry like an old battery. He recapped it and...BOOSH LOUDEST AMP ON THE PLANET !!! We even left the original RCA power tubes in and they still don't need to be replaced..
 
#9
It is easy to tell what type of tubes are in your amp. Look through the metal screen at the back of the amp at the row of six big tubes plugged into the bottom chassis. If each tube has a wire that comes out of the chassis and connects to the top of the tube, you have 6146B's in there. If there is no wire, you most likely have 6550A's.

In any event, if your amp has never been serviced, it is going to need some work. A good cleaning for starters, new power supply capacitors, a three-conductor power cord, and possibly some component changes if parts are out of spec. You may or may not need new tubes.

As a place to start, there is a lot of useful information here.
 
#11
Everyone here is assuming that the problem is with the power tubes, and it might well be, but it could also be an aged or damaged component further up the line. If you're not desperately broke, take it to a good tech.

Unless you've got a very good reason not to, I'd want to keep the amp stock. I successfully resisted the urge to replace the 6C4 socket on the pre-amp board of mine with an easier-to-find-and-fill 12AU7 socket (a 6C4 being equivalent to half a 12AU7), back in the dark days before internet tube vendors and ebay, and I'm glad I did.
 
#12
Thanks everybody! A lot to think over and check into. Would the tube power/life be visible strictly by the glow they emit? Or could that glow be stifled or reduced by any of the other issues you guys have posted? The "leaked capacitors" sounds especially intriguing. Thanks again, evwryone!
 
#15
It could be and sounds like it could be as simple as a bias adjustment, which is very easy if you know what you're doing. But take it to a tech, also buy 6 off 10R 5W wirewound resistors, they come in two sizes 22x10x10mm or 35x9x9mm, you need the 22mm (7/8ths). These he can fit if needed, the reason I think you should supply these is, Tech's are notorious for fitting (if they can't get them to hand) parts that are close enough.
 
#18
Mr. Foxen said:
If you need to be tracking down the right parts to fit to stop the tech bodging it, you need to track down a new tech, not new parts. If they tell you they can't find something, and have something else that will do, sure, but not casually.
Click to expand...

Will it hurt to source a known part and supply with an amp to a Tech you have never been too?, I don't think so. You never know they might fix it there and then.
 
#20
Pyntch said:
Thanks Jimmy! That's great news! The glow is minimal, but not nonexistent in one of the large tubes, the rest are fine. Long shot, but can anybody recommend a trustworthy tech in upstate/ western NY?
Click to expand...
If one tube is visibly behaving differently like that, it *could* be that that's your only problem. However, with tube amps, just swapping out that tube for a good one isn't the end of the story. There's enough variance in tubes of the same type, even from the same manufacturer, that you really want to re-bias the power stage every time you change a tube. That's a whole lot easier on old SVTs than on most amps - there are test points and a bias pot behind the back panel on my old blueline. But at least for the first time around, do take it to a tech.

In terms of parts substitutions, yeah, it can be a problem with some techs. When I first got my SVT many years ago, it kept blowing up the huge ceramic-clad resistors that are there to level loading across the three tubes of each phase of the power stage. Studying the schematic, I realized that someone had replaced them with a *slightly* higher resistance value, not realizing that, in that circuit, this caused them to soak up exponentially more power, and explode when the 6C4 acted up. A good tech won't do approximate substitutions, but even a mediocre tech will take explicit orders - "no part type/value substitutions, please".

As for finding a good tube amp tech in your area, I don't know any (being in California), but I'd suggest you search/post on some guitar forum sites. There are a whole lot more guitarists out there with tube amps than there are bassists.
 

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