CHAMP ELECTRONICS -" THE VINTAGE VALVE AMP HOSPITAL"

NOTTINGHAM, ENGLAND

REPAIR OF THREE VERSIONS OF THE AMPEG "SVT" AMPLIFIER:

AN SVT-II, AN SVT-II PRO, & AN SVT-AV.

1. THE SVT II AMPLIFIER

OK, as I said in the introductory text, the SVT is a good and powerful bass-amp......when it is working correctly. However, when they have problems they can be a pig to work on! If I was forced to choose between the various versions, my pick would probably be this one, the SVT 11, with all the output tubes in a row. It is probably the easiest to work on, if the term "easiest" is correct here!

That's Mervin's (Doctor Valve…from Australia) thumb and fingers in the bottom left of the photo. We both hate these amps being on PCB.

Looks pretty impressive though, with the six tubes in a row.

Heavy mothers too!

Everything out again to be able to work on the PCB.

Here you can see that the centre meter socket (for checking the bias) has lifted out of the print. This is quite common with these, as the flow soldering isn't that good and tends to dry-out over time.

2. THE SVT II PRO AMPLIFIER

Now, this one is my biggest pet-hate of all the SVT range. With two PCBs sandwiched above each other, they are a complete pig to work on!

The large main PCB underneath with the output tube's PCB mounted directly above it, resulting in very little clearance between the two.

Every bloody thing out!

The output tubes' PCB is now exposed with the removal of the large main PCB. Also the AC power voltage selector board (bottom right) removed. This board can be very daunting if one is not familiar with it, when selecting different country voltages.

OK, look virtually in the middle of the photo and you can see a circle marked on the PCB. This is where a cap that I have removed should be. Now look slightly lower and a little to the left; there is a cap in place here but you can see it is bent downward. These two caps are the plus-and-minus 15 volt rails for supplying all the chips. First, these two caps are usually 16 volts working, which puts them right on border-line, and in-fact they do usually run quite warm! 25 volt caps are a must here! Secondly, if they aren't leaning over far enough, the un-insulated top of either of them can touch the underside of the output tubes' board, with devastating consequences…as was the case here!

I rest my case!

The output tubes board out for reconstruction.

Cleaned and re-wired accordingly.

Putting everything back into place. Phew, what a pain these are!

3. THE SVT-AV AMPLIFIER

I have done quite a few of the SVT-AV amps, and for some stupid reason I have never taken any photos of them complete in their case. The next time one comes through the workshop, I will take some external photos and add them to this article. The power-amp and separate pre-amp section (which is mounted at the front/top of the wooden case) are shown here.

The voltage-selection board again. All the SVT range uses two power transformers which, along with the cooling fan, all terminate back here onto this board.

And again, the typical underside PCB of the power-amp section.