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Ampeg SVT opinions

9/16/1999 9:57 PM
Marc	Ampeg SVT opinions I would appreciate some advice on an SVT a buddy of mine wants worked on, Here goes; are the EI 7247's good replacements or should I go NOS? Can 100/100 LCR's be used to replace the 100/40mfd FP cans on the chassis with out any problems other than mounting? The FP cans are isolated from the chassis so the sections can be run in series... the LCR's are about a 1/3 the cost of the AERO fp's and the LCR's are closer in mfd values... The amp has it's original caps and preamp tubes. Are there any other common problems with SVT's that I shold be on the look out for? Thanks in advance Marc

9/16/1999 9:57 PM

Marc

Ampeg SVT opinions

I would appreciate some advice on an SVT a buddy of mine wants worked on, Here goes;

are the EI 7247's good replacements or should I go NOS?

Can 100/100 LCR's be used to replace the 100/40mfd FP cans on the chassis with out any problems other than mounting?

The FP cans are isolated from the chassis so the sections can be run in series...

the LCR's are about a 1/3 the cost of the AERO fp's and the LCR's are closer in mfd values...

The amp has it's original caps and preamp tubes.

Are there any other common problems with SVT's that I shold be on the look out for?

Thanks in advance

Marc

9/16/1999 10:46 PM
Psycho Bass Guy	EI 7247's are really hit and miss; some are really noisy or microphonic. If they sound good, go with them. Watch for interstage distortion(usually some sort of oscillation) and you might want to consider a dual bias control, as there are really two different power sections running off of the existing bias control. Also be very aware, especially on the pre-Magnavox SVT's, that the circuit will vary to differing degrees from Magnavox's published schems (these are the most common). (Mine is a Selmer, and just try to pin that schem down!) Chances are (and this is highly dependent as to who owned the company when it was made i.e.-Ampeg, Selmer, or Magnavox, these are the only three who made the "real" SVT. All three carry the Ampeg name, but on the back grille of the amp, there will be a tag saying either: just "Ampeg" or "Ampeg, a division of the Selmer Company", or "Ampeg, a division of the Magnavox company") those caps need replacing. Even if the amp sounds fine, it will help it in terms of performance stability and consistency. Good luck as this beastie has a tendency to get really touchy sometimes, but when it works, it is the KING of all bass amps. PBG

9/16/1999 10:46 PM

Psycho Bass Guy

EI 7247's are really hit and miss; some are really noisy or microphonic. If they sound good, go with them. Watch for interstage distortion(usually some sort of oscillation) and you might want to consider a dual bias control, as there are really two different power sections running off of the existing bias control. Also be very aware, especially on the pre-Magnavox SVT's, that the circuit will vary to differing degrees from Magnavox's published schems (these are the most common). (Mine is a Selmer, and just try to pin that schem down!) Chances are (and this is highly dependent as to who owned the company when it was made i.e.-Ampeg, Selmer, or Magnavox, these are the only three who made the "real" SVT. All three carry the Ampeg name, but on the back grille of the amp, there will be a tag saying either: just "Ampeg" or "Ampeg, a division of the Selmer Company", or "Ampeg, a division of the Magnavox company") those caps need replacing. Even if the amp sounds fine, it will help it in terms of performance stability and consistency. Good luck as this beastie has a tendency to get really touchy sometimes, but when it works, it is the KING of all bass amps.

PBG

9/17/1999 2:44 AM
Marc	Hey PBG: thanks for the backround next time I get it in the shop I'll try to figure out which company made this one. What do you think about the LCR's in place of the old cans? When I eye balled it they looked like they would fit OK. Might have to drill new mounting holes... It has dual bias adjustment jacks in the front of the bottom chassis and it has a hum balance pot and a harmonic balance pot for the 12BH7's. Is that what's on yours? It is one HEAVY sucker, too. my little turntable workbench didnot like it. Thanks Marc

9/17/1999 2:44 AM

Marc

Hey PBG:

thanks for the backround next time I get it in the shop I'll try to figure out which company made this one. What do you think about the LCR's in place of the old cans? When I eye balled it they looked like they would fit OK. Might have to drill new mounting holes...

It has dual bias adjustment jacks in the front of the bottom chassis and it has a hum balance pot and a harmonic balance pot for the 12BH7's. Is that what's on yours?

It is one HEAVY sucker, too. my little turntable workbench didnot like it.

Thanks Marc

9/17/1999 3:38 AM
Psycho Bass Guy	Marc, Mine only has one bias control in stock form. Everything else sounds the same. None of the main caps in mine were original when I got it,(for 250 bucks are you going to complain?) so I say try them and see. Don't worry about appearance too much inside the chassis. My tech buddy(this was before I started messing inside amps) used computer grade caps and built a metal box around them, so I can't tell you what they are. He is using it at the moment anyway. 93 lbs is what he says, but the bathroom scale says an even 100. The plate loads and the power supply in mine have also been changed to accomodate KT90's. (It seemed like a good idea at the time!) I find it interesting that Genalex, a British military contractor, is just starting back its KT88 production, and the Brits just happen to bomb the factory that competes against them. Oh well, I am probably paranoid. PBG

9/17/1999 3:38 AM

Psycho Bass Guy

Marc,

Mine only has one bias control in stock form. Everything else sounds the same. None of the main caps in mine were original when I got it,(for 250 bucks are you going to complain?) so I say try them and see. Don't worry about appearance too much inside the chassis. My tech buddy(this was before I started messing inside amps) used computer grade caps and built a metal box around them, so I can't tell you what they are. He is using it at the moment anyway. 93 lbs is what he says, but the bathroom scale says an even 100. The plate loads and the power supply in mine have also been changed to accomodate KT90's. (It seemed like a good idea at the time!) I find it interesting that Genalex, a British military contractor, is just starting back its KT88 production, and the Brits just happen to bomb the factory that competes against them. Oh well, I am probably paranoid.

PBG

9/17/1999 5:01 AM
Jeff	Our bass player has model SVT. He runs through a newer SVT 8x10 cab. His problem is, too much breakup before he can get the stage volume loud enough. It has Svetlana 6550's in it. Would a different tube help this problem?? Thanks! ::Jeff

9/17/1999 1:20 PM
Psycho Bass Guy	output tubes Jeff, An SVT ought to be be cleaner than that. It sounds like the amp and not necessarily the tubes need looking at. That's not saying they're not bad, but Svetlana 6550's are good tubes and should perform better. The SVT has a special fuse-type circuit on the ouput tubes where if one tube goes down the amp shorts it out and keeps running, but you have a major loss of power due to the imabalnce and the fact that the amp is set up to run six tubes. Check your current draw and make sure all six tubes are really running. Is your bass player's model one of the "real" SVT's or is it one of the newer SLM models with a master volume? If it is older and one of the non master volumes get it into the shop immediately. It needs recapping and probably a bunch of other work as well. If it is one of the SLM (St. Louis Music, same people that own Crate) it may be a case of poor construction, in which case it would have to be modded just to perform as it should. Every SLM SVT I have ever tried distorts way too early and has no punch whatsoever. The only way to fix this is to scrap the current limiting circuit in the SLM models and change out the filter caps to the 1000v value. (more voltage will make the amp more stable). SLM SVT's like KT90's better than the old ones and -maybe- a set of 'em might be in order. (Since NATO bombed the EI factory in Nis, they go for over $75 a pair if you can find them and remember you need two mached trios that are fairly close to each other. That's a vey tall order and way expensive.) They fixed an SVT II which couldn't be modded due to warrantee. (My tech buddy was one of SLM's certified techs for about three months before he dropped them out of disgust.) Have a knowlegeble tech check the amp out. It can KILL you if you don't know what you're doing. Unless you play at the threshold of pain,(in which case nothing will help short of more amps and cabs) a 6550 equipped SVT should give ample clean volume. Get it checked out. PBG

9/17/1999 1:20 PM

Psycho Bass Guy

output tubes

Jeff,

An SVT ought to be be cleaner than that. It sounds like the amp and not necessarily the tubes need looking at. That's not saying they're not bad, but Svetlana 6550's are good tubes and should perform better. The SVT has a special fuse-type circuit on the ouput tubes where if one tube goes down the amp shorts it out and keeps running, but you have a major loss of power due to the imabalnce and the fact that the amp is set up to run six tubes. Check your current draw and make sure all six tubes are really running. Is your bass player's model one of the "real" SVT's or is it one of the newer SLM models with a master volume? If it is older and one of the non master volumes get it into the shop immediately. It needs recapping and probably a bunch of other work as well. If it is one of the SLM (St. Louis Music, same people that own Crate) it may be a case of poor construction, in which case it would have to be modded just to perform as it should. Every SLM SVT I have ever tried distorts way too early and has no punch whatsoever. The only way to fix this is to scrap the current limiting circuit in the SLM models and change out the filter caps to the 1000v value. (more voltage will make the amp more stable). SLM SVT's like KT90's better than the old ones and -maybe- a set of 'em might be in order. (Since NATO bombed the EI factory in Nis, they go for over $75 a pair if you can find them and remember you need two mached trios that are fairly close to each other. That's a vey tall order and way expensive.) They fixed an SVT II which couldn't be modded due to warrantee. (My tech buddy was one of SLM's certified techs for about three months before he dropped them out of disgust.) Have a knowlegeble tech check the amp out. It can KILL you if you don't know what you're doing. Unless you play at the threshold of pain,(in which case nothing will help short of more amps and cabs) a 6550 equipped SVT should give ample clean volume. Get it checked out.

PBG

9/20/1999 3:58 PM
Graywater	Hey Psycho, Well, I also do SLM warranty and I would be the last to state that they couldn't use some reliability improvements. But the majority of warrantly problems are QC related - mostly poor solder joints. But the reason I write is to state that SLM products really aren't that different from most current large American/other manufacturers. I seen funky Peaveys (good boards though), really poorly made SS Fenders, and some Marshalls (such as the Valvestate I'm currently working on) that are also cheaply made. It's like labor (and maybe partially due to), everyone competes that they have cheaper labor costs and the result is that no one is paid a living wage (Britian is currently "marketing" its citizens as the cheapest labor cost in the EU). So, one company markets an "inexpensive" amplifier and all of the other companies jump on the bandwagon to lower the cost/quality. Consumer's have gotten used to the price of electronics dropping steadily but this is mostly due to soild state manufacturing/design improvements. Tube technology was pretty mature at the end of WWII and there really isn't much way to lower the price of a tube amp other than lowering quality. And, in constant dollars, tube amps are cheaper than ever for the same features/output power. Ya gets what ya pay for. GW

9/20/1999 3:58 PM

Graywater

Hey Psycho,

Well, I also do SLM warranty and I would be the last to state that they couldn't use some reliability improvements. But the majority of warrantly problems are QC related - mostly poor solder joints. But the reason I write is to state that SLM products really aren't that different from most current large American/other manufacturers. I seen funky Peaveys (good boards though), really poorly made SS Fenders, and some Marshalls (such as the Valvestate I'm currently working on) that are also cheaply made. It's like labor (and maybe partially due to), everyone competes that they have cheaper labor costs and the result is that no one is paid a living wage (Britian is currently "marketing" its citizens as the cheapest labor cost in the EU). So, one company markets an "inexpensive" amplifier and all of the other companies jump on the bandwagon to lower the cost/quality. Consumer's have gotten used to the price of electronics dropping steadily but this is mostly due to soild state manufacturing/design improvements. Tube technology was pretty mature at the end of WWII and there really isn't much way to lower the price of a tube amp other than lowering quality. And, in constant dollars, tube amps are cheaper than ever for the same features/output power. Ya gets what ya pay for.

GW

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