Ampeg SVT 1970's

[Dano]

Does anyone still use or is familiar with the characteristics of the 1970's Ampeg SVT Bass Amp.

I have one here and when both channels are set equally (tone controls set to 12 o'clock, tone switches set to zero), channel one is not as loud as channel two.

If the channel two volume control is set to 10 o'clock, the channel one volume control has to be at 12 o'clock in order for the sound to be equal in loudness.

Additionally, if we set the ultra low switch to the + position on channel two, then both volume controls will mirror each other in terms of the volume output.

Is this the way the amp is supposed to be?

Any Experts who use this amp?

You know, the one's with the engine hoist in the van.

Thanks,
Dan

[bigbottomend]

Only 4 years later i find this post.

Exactly the same behaviour mine has and i've checked everything i can from the schematics.
Rolled the tubes, bought new ones, even had a full cap job but channel 1 is still quieter.
I'm now thinking that this is normal for them although i have a friend who said his was the opposite with channel 2 being quieter. Or it might be the 1 meg volume pot ?

I assumed that they were supposed to be the same in terms of volume with 12 o'clock being full volume, past that was to get the output tubes to overdrive ?

Steve

[J M Fahey]

It´s probably normal.
Anyway that´s not a problem by itself.
And the "12 o´clock rule" is not set in stone, nor written or specified anywhere, it´s just something that happens often, but not always, by a long shot.

[soundguruman]

Finally, a post about a real SVT.
Not the junk ones, full of transistors, made by (omitted) in China, and sold as: "SVTs"
You can build a junk amp and label it "ampeg" on the outside but it's still (omitted) crap on the inside.
Yes, a real SVT. It's normal for it to do that. Yes, there are experts here.
Real SVTs were made in USA by Magnavox. If you have a real one, don't let it go.

[Tom Phillips]

...It's normal for it to do that...

And unless the difference between channels is really radical I encourage the users to stop worrying about the absolute position of the control knobs. The important thing is that one can find a setting that produces the sound they want. It doesn't matter if the control is at 12 O'clock or some other setting. I hear similar things about Fender amps especially concerning the rotation of the volume pot. A guy will complain that his Pro Reverb must be set on volume #4 to be as loud as his buddy's set on #3. One solution is to loosen the set screw and reposition the knob.

[Ronsonic]

Finally, a post about a real SVT.
Not the junk ones, full of transistors, made by (omitted) in China, and sold as: "SVTs"

They aren't made in China. They're made in Vietnam.

[soundguruman]

By the same factory that makes Hartke?

[J M Fahey]

soundguruman said:

By the same factory that makes Hartke?

You missed it again

No, by the factory that makes Crate.

Why do I waste my time here?
Somebody who confuses China with Vietnam will also confuse Hartke with Crate ... and many other things too.
Oh well.

[soundguruman]

Hartke says made in Vietnam too.
I'm starting to suspect that it's the same communist plot. Those pinko/commies are flooding our country with exploding amplifiers.
Why do you waste your time? Could it be that you need a real job?

[J M Fahey]

I *do* have a real job.
But after some time I sit here to relax a little, chatting about interesting things with cool guys.
And sometimes ... what do I find here, mixed with all the good info and cool ideas?
Yes ........... you guessed right

I must ask God (or Freud) to forgive me for this, but I also have some pleasure making fun out of the village idiot.
I know it´s evil, but sometimes I can´t resist.
Forgive me.

[soundguruman]

So IS it an evil communist plot? or NOT?

[Ronsonic]

So IS it an evil communist plot? or NOT?

Or .... and this is a frightful possibility .... does it mean we have "won" ?

[soundguruman]

I personally, submit to and welcome our new commie elitist over-lords.
I thought all the long that the threat was transistors, but I was cleverly deceived.
The real devil lay hidden in their political philosophy.
Our experiment in democracy has failed, I concede there will no longer be American Made Amplifiers.

[Rick Erickson]

[Somebody who confuses China with Vietnam will also confuse Hartke with Crate ...]

and what exactly Is the difference?

[soundguruman]

There have been disturbing similarities.

[J M Fahey]

Like what?
Both have slant eyes and eat rice with chopsticks?

[soundguruman]

To answer the question, yes that's normal.

[Enzo]

Hmm, odd. I am at the moment working on a made in California fender, and there are certainly tons of USA made amps from Mississippi made by peavey. Last I checked those states were still in the USA.

[J M Fahey]

Not forgetting Mesa Boogies.
Last time I checked, Petaluma, California was *still* in tyhe USA.

[soundguruman]

Not forgetting Mesa Boogies.
Last time I checked, Petaluma, California was *still* in tyhe USA.

Yes, it's still "sort of" assembled in USA...

[Tage]

Hey back to the OP, I have looked into the schematics and channel 1 and 2 seem to be quite different. But my experiance with SVT's is limited to being pummled by them at concerts never worked on one...

http://www.webphix.com/schematic%20h.../svtpreamp.pdf

Channel one has two more gain stages and both are 12dw7's dc coupled to cathode followers so I would expect that to be the louder channel, but it also has the mid control stuff in there... I'd be checking those old 12dw7 to make sure they didn't get swapped out for somthing else.

[mac1amps]

The result of Ch 1's mid/ inductor network has somewhat of a "loading" effect on the signal which is why it may not have the same gain when set similar to Ch 2.......'like the man said, don't fret about the setting positions, plug in and play!!

[Frankthetankbass]

so i'm looking for a fuse for my 70's SVT it says 10A/250V and when i see them online i see 10A/250v 5mmx20mm and 10A/2500V 6mmx30mm. does anyone know which one is for this head? And as i understand it needs to be a slow blow as i understand.

[Enzo]

Those are physical size, nothing more. Th regular 1-1/4" fuse is 30mm, the smaller fuses like on imprt gear are 20mm. Get out a ruler and measure the length, it is either 20mm or 30-32mm. An American amp from the 1970s probably did not use 20mm fuses. I'd expect to find common inch and a quarter fuses.

[Frankthetankbass]

yes thank you -Measure what a great idea-silly me.....It's 1 1/4 thanks

[txstrat]

...both are 12dw7's dc coupled to cathode followers...

Cathode followers cannot provide a voltage gain higher than 1. The 2nd section of the 12DW7 even has a much smaller amplification factor (of about 20) than a 12AX7.
Therefore I would expect the first channel to be less loud.

Hence, the amps behavior is normal.

Hope this helps