Ampeg SVT Tube Bass Amp -Mods

[Scodiddly]

The only appropriate mod for an SVT involves wheels... those things are just too damn heavy. They do sound nice, though - even at low volumes.

 

[jensenmann]

The only mod that I did with my SVT was to check out a lot of different (matched) tubes. Finally I ended up with some Ruby Tubes KT88 which I liked most. Another interesting Tube might be the EL34 which gives less power but nice overdrive. Concerning reliability I´d say that these beasts are not better or worse like any old Marshal, Fender,... My SVT is like a human. Sometimes he catches a little cold, sneezes or makes some funny sound but a few days later everything´s gone. It´s runnung since 8 years without any service.
I definitely see no need to mod that sound. It´s raw rock´n´roll. That´s how it is supposed to be. For a different sound I´d get a different amp.
cheers
Jens

 

[jensenmann]

btw, if you carry your ampeg a lot you´ll get used to it and you´re going to have a strong back. Then you are ready for a flightcase :green:
Jens

 

[Rob Flinn]

Finally I ended up with some Ruby Tubes KT88 which I liked most. Another interesting Tube might be the EL34 which gives less power but nice overdrive.

An EL34 sounds like an odd substitution since its a pentode and a KT88/6550 is a beam tetrode. In the KT88 the beam forming plates are internally connected to the cathode, whereas in the EL34 you need an external connection from cathode to suppressor grid.

Are you sure this is right?

 

[jensenmann]

To be honest it´s a long time ago that I tried this out. I´m not at all into tubes and did the test at a local amp repair place with one of their technicians. Maby it was a different tube, but I´m pretty sure it was an EL-type :?
jens

 

[oobedoob]

not only have I hurt my back with those things.....

I have a nice scar where an SVT almost severed my right index finger. Got it wedged in between the amp and the studio door jamb as I was loading in for a session. Bass player was waaaaay too skinny to be playing one of those things..... Damn, that hurt. Played all the basic tracks holding the pick between my thumb and middle finger.

I def. agree with the others--don't mod it.

 

[NewYorkDave]

[quote author="Gus"]you picked it up to your bench????????

wow!

I worked on the svt on the floor.[/quote]

In hindsight, it was not a good idea at all, but I had hefted SVTs on to my bench before. I was younger and stronger then! But in that particular case, I picked it up "wrong" and hurt myself. I worked on more SVTs later on, but that was the last one I attempted to lift by myself.

Putting wheels on an SVT seems a very worthy "mod" indeed.

 

[BYacey]

If a person works on these on a regular basis, it wouldn't hurt to install a chain hoist on a rail over the workbench!

 

[jrmintz]

not only have I hurt my back with those things..... I have a nice scar where an SVT almost severed my right index finger. Got it wedged in between the amp and the studio door jamb as I was loading in for a session.

I picked it up "wrong" and hurt myself

There are a lot of sacrifices we make and risks we take for the career decisions we've made. I can't see risking your health for a bass amp, no matter how good it is. I like SVTs but a GK800RB is about 90% as good if you have a good sounding instrument, and it's a lot easier to carry. I'm still waiting for someone to design an inflatable bass amp.

:green:

 

[clintrubber]

Ampeg SVT, hmm, does ring a bell. It's this amp, right ? :wink:

 

[jensenmann]

:shock: :shock: :shock: :shock: :shock: :shock: :shock:
I NEED THIS BEAST!!! WHERE CAN I GET IT FROM???

is there a thread for diy forklifters around?

Rock´n´Roll
:guinness: :guinness: :guinness:
Jens

 

[clintrubber]

I NEED THIS BEAST!!! WHERE CAN I GET IT FROM???

I'm not sure how readable the description was, but as it seems only a few were made.
Uhh, and maybe the pic wasn't the whole setup - if they did it well & true to the original idea they should have provided two cabs for each amp :wink:

 

[Scodiddly]

[quote author="Rob Flinn"]

Finally I ended up with some Ruby Tubes KT88 which I liked most. Another interesting Tube might be the EL34 which gives less power but nice overdrive.

An EL34 sounds like an odd substitution since its a pentode and a KT88/6550 is a beam tetrode. In the KT88 the beam forming plates are internally connected to the cathode, whereas in the EL34 you need an external connection from cathode to suppressor grid.

Are you sure this is right?[/quote]

I'd be more worried about the max plate voltage on an EL34 - isn't 500vdc the absolute maximum for an EL34? The 6550 and KT88 are designed for higher voltages and power dissipation.

 

[evil grill]

I'd be more worried about the max plate voltage on an EL34 - isn't 500vdc the absolute maximum for an EL34? The 6550 and KT88 are designed for higher voltages and power dissipation.

maximum rating for el34 is
platevoltage: 800 V (2000 V when plate current is 0 mA)
plate power dissipation: 25W

U*I=P. as long as the current is´nt too high it should work

 

[PRR]

> An EL34 sounds like an odd substitution since its a pentode and a KT88/6550 is a beam tetrode.

The difference is in the patents. RCA invented a different (not particularly better) way to build a pentode with beam-forming plates instead of a wound grid. They had the tradename Beam Power Pentode. The shape of the electric field is a little different, but it is still a pentode. The grid-cathode interface is isolated from plate swings by G2, plate secondary emission does not bounce back to G2. The so-called Beam Tetrode is also a pentode.

The 6L6 and 6550 families are high-strung with a hard knee. The EL34 has less severe grid control and goes a little triode around the knee. It makes less power, over a wider range of impedances, and for most useful loads it goes soft before it clips.

> In the KT88 the beam forming plates are internally connected to the cathode, whereas in the EL34 you need an external connection from cathode to suppressor grid.

Yeah, you have to check all the pin connections any time you change tubes. H and K are the same place on most octals, and P and G1 are the same on most power octals, but G2 ends up anyplace and G3 may or may not be strapped to K.

> I'd be more worried about the max plate voltage on an EL34

The factory claimed 800V and the app sheet showed 100 Watts from a single pair. To get there you HAD to have regulated 800V and a just-right load: if anything was a little off, instant melt-down. And some folks say 800V is just too much for the octal base, even with ribs.

> The 6550 and KT88 are designed for higher voltages and power dissipation.

A genuine 6550 has a larger plate of the best plate-stuff, and the 35W-40W rating is conservative. EL34 is 25W rating: they take more, but 35W is way too much for good life.

If you really bias an SVT for 25mA and 600V, that's only 15 watts per plate at idle. No reason a EL34 could not idle that way. Dissipation would be higher at full power: an SVT with EL34s cranking full power sine waves would not last decades like good 6550 do. But it might groove on music all night: if not clipping, it would just be hot; if turned past "11" grinding out pure square-wave distortion the dissipation actually goes down.

No 6L6 is rated 600V, but good late-1950s 6L6GC will stand it. 7027 is another good POWER-tube and has decent voltage ratings, but you gotta check the wiring on the socket. 8417 is a high-gain 6550: do NOT put 8417 in any amp you love or even like, unless you know the risks.

Youse guys think an SVT is a big amp. The 8417, if you can tame it, makes as much power as 6550. For a while I was road-showing with a dozen 8417s in three uprated Bogen PA amps, retired from kine duty. Something over 450 Watts of glass and iron. That's not what killed my back, but hefting those beasts sure was not a healing experience.