CHAMP ELECTRONICS -" THE VINTAGE VALVE AMP HOSPITAL"
REPAIR OF FOUR VERSIONS OF THE AMPEG "SVT" AMPLIFIER:
AN SVT-II, AN SVT-II PRO, AN SVT-AV/CLASSIC & A Mk1 6146 OUTPUT TUBES.
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
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/CLASSIC AMPLIFIER
I have done quite a few of the SVT-AV amps. 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.
4. SVT Mk1 WITH 6146 OUTPUT TUBES
This one actually came in to my good friend John Wood. It had a burnt-out power transformer and John got the job of re-winding it & servicing the
An original Mk1 version with 6146 output tubes.....you don't see many of
Out & the transformer removed.
Pretty scruffy wiring...has probably had a lot of work done through it's
The transformer stripped.
And finally the pre-amp still mounted in the case. Lovely old amp!