Ampeg SVT4Pro driver heatsinks?

[Mars Amp Repair]

Hello folks,
I have battled with this amp & have finally gotten all the bugs (prior tech & natural created) and now wonder if there are any heatsinks used on the driver transistors or if Ampeg decided to leave them off at some point. I can't really trust the fact that they are not there on this amp as a prior tech didn't show much skill in what he had done to the amp.

My recollection is that the heatsinks are not used, but I really don't want this amp to come back

These heatsinks just push on to the driver transistors & have two cylidrical 'silos' on each side of the transistors. You can see the heatsinks outlined on the pcb screening. Both transistors are between the 2 massive power heatsinks, so they probably get adequately cooled by the fan...but I just want to be certain.

Ampeg says they have the sinks in stock, but cannot sell them as there is no price code or some such nonsense. The heatsinks almost have to be of the variety originally intended as the space requirements & board layout won't safely accommodate other types.

Can anyone recall if the SVT4Pro actually utilizes these heatsinks?

Q102, Q105, Q202, Q205 can be seen on attached pictoral Thanx, glen

[MarkusBass]

Yes, they are used in the amp. You can try to find similar ones (that will fit into the amp).

Happy New Year,
Mark

[tim]

Better you than me Glen...I don't work on those beasts any longer. I hate them... When they go, they go catastrophically and it's usually a 4-6 hour job to remove circuit board, find and replace all the blown parts, clean off the scorch marks, replace the circuit board and hope you found all the bad parts, plus the cost of parts...when I tell my customer how much it will cost, they usually bow out. I still haven't found a good way to connect that amp up to measure and set idle current either...maybe someone could clue me in...

[MarkusBass]

What about just measuring the voltage on source resistors (0.47 Ohm) and recalculating the current? You can measure it between source of a MOSFET transistor (carefully ) and the output of the amp. In this way you can verify whether MOSFETs are matched.

Mark

[tim]

ahhhhh, it's the "carefully" part that gets me every time. It would have been nice if Ampeg had designed in easily grabbed test loops to hook onto when you're setting bias. Trying to hold two test probes on tiny spots and trying to get to the set pot where they bury them with your third hand is nigh impossible, at least for me...

[MarkusBass]

I use miniature test clips like this one: http://www.tme.eu/katalog_pics/6/7/6...24c/d-6010.jpg
In this way I can do the measurements just with 1 hand

Mark

[Mars Amp Repair]

Yeah,
they are a beast to work on just logistically speaking. I have found ways around the idle measurement by tapping the Source resistors at other locations. I try to do that before I put the beast back into its can.

I was hoping they discontinued those heatsinks...I still have a shot at Loud as the gal said it was a matter of getting them in the system...you know how corp folks are about doing anything outside their little box ;-]

I have gotten as I've mentioned before to a kind of Zen with these Ampegs...a few minutes in the lotus postion & I can usually keep myself cool...if I can just get back out of that position!!

Yes, VERRRRRRRRY careful is the name of the game with these. Thanx all, glen

[Mars Amp Repair]

Yeah mark,
Rat shack used to carry those in a pkg of 5 that you could put your own wires on. They don't anymore. g