Tuning up a vintage SVT, any advice?

[nateflanigan]

I feel like I've been circling these things for the past 20 years and last week I finally picked one up. I played it a bit by myself, seemed cool, but today when I got to use it at practice it was kind of blah. My 250w Galien Krueger 400b really put it to shame. Seems unthinkable, right? Before I bail on it I'd really like to open it up and see if I can get it tuned up. Any advice? Anything specific to look for?

[martin manning]

I'd start by looking for the usual things in any older tube amp: tired tubes and aluminum electrolytics. Open it up and see what's in there.

[HeeBGB]

I'd start even more basic than what Martin is saying I'd tension the tube sockets clean them with deoxit and also clean the pots and a new set of tubes first.

[DonMoose]

I'd start even more basic than what Martin is saying I'd tension the tube sockets clean them with deoxit and also clean the pots and a new set of tubes first

(No DeOxit on the pots - use FaderLube there)

[HeeBGB]

I'd start even more basic than what Martin is saying I'd tension the tube sockets clean them with deoxit and also clean the pots and a new set of tubes first

(No DeOxit on the pots - use FaderLube there)

I haven't heard anything about this before is deoxit bad for the pots?

[Reeltarded]

Some folks have had old carbon traces just wash away. I haven't but i've heard of it.

[rock_mumbles]

DeOxit will melt some plastics ... so it can damage some types of pots some end up completely non-working ... others just turn really hard

FaderLube is amazing stuff

[M Fowler]

Sounds like I better get some faber lube

[Firestorm]

The fader stuff used to be called CaiLube. Caig changed the name to Deoxit Fader just to keep us all confused.

[Firestorm]

As to the SVT itself: apparently getting the output sides balanced is the trick. Weber published a piece on it, KO'C has a whole section in the third book. These things scare me: serious voltage, serious power. There are few models with significant differences.

[mark enger]

My bro-inlaw sold his after a costly 2 years he was forever putting money
in his, his had bias controls on rear panel does yours? mark

[nateflanigan]

Ok, spent some time at the practice space after work checking out the amp. So first things first, the original schematics were still in the cabinet! They're dated 1975. So that's cool.

http://www.el34world.com/charts/Schemat ... reAmp_.pdf
http://www.el34world.com/charts/Schemat ... _SVTV9.pdf

- The filter caps are nichions, couldn't say how old they don't look extremely new.

- Tubes, Svetlana 6550's, with tubestore decals on them.

- Preamp tubes,
v1 raytheon 12w7
v2 tung sol 12ax7
v3 jj something, couldn't read
v4 jj something, couldn't read
v5 jan-phillips 6c4

- On to the biasing procedure, step 2a checked out fine. Step 2b however was way off, so I adjusted VR2 to as close to 0 as possible. This was a big improvement in the output distortion.

- I didn't have the gear with me to do step 3, but I'll get that together.

- Still switching back and forth between the GK and the SVT, the low end was pretty murky on the SVT and it was hard to match volumes with out the SVT getting really blown out sounding.

- So, I thought I'd try running the GK pre out to the SVT power amp in. Holy Moly, sounds AMAZING and LOUD.

Now I know the power amp is working, so that's good. But I guess I gotta figure out if I just don't like the Ampeg pre, or if it needs some attention. At least the pre-amp tubes aren't too expensive.

Thanks for the tips about TUT and weber, I'll check that out. I have both deoxit's at my studio space.

[martin manning]

Sounds like someone has been through this amp fairly recently. Good idea to cross-connect the power amp! All the really expensive stuff seems to be working fine. Tubes are 1x 12AX7, 3x !2DW4, and 1x 6C4 per the schematic. JJ is reproducing the 12DW4, and NOS 6C4's are not expensive if you need that. The preamp schematic has voltages listed, so I'd start by checking all of those. Swap out tubes to see if you get any improvement (you should have a spare 12DW7 or two and a 6C4).

[Reeltarded]

I love SVT but only with 8x10 because that takes the clouds out of the lowend. Modern expectation doesn't really favor the frontend.

GK is a hifi. SVT is a bulldozer.

[nateflanigan]

All the really expensive stuff seems to be working fine.

Yeah this is a big relief, thinking about spending, $300 or so on power tubes and filter caps just to see, well I wasn't looking forward to that.

I love SVT but only with 8x10 because that takes the clouds out of the lowend. Modern expectation doesn't really favor the frontend.

GK is a hifi. SVT is a bulldozer.

The EQ profile is so different between the 810's vs the 2x15's. I've found that I need to cut the low mids and add a good amount of treble with the 8x10 but the low end is just perfect. With the 15's it's more about dialing back the lows so they're not over whelming, and warming up the upper mids. To my ears anyhow.

The GK is certainly more Hifi, but it is a really early all discreet 400b, so it's not the same as a modern GK. They're neat heads, the power amp leaves a bit to be desired though.

I have an Acoustic 360 pre-amp pedal I made, I'm going to try running that with the SVT power amp, whilst I await new pre amp tubes.