Trace Elliot GP7 300 Watt version bipolar bear question

[Lee_ranaldo]

Hello forum!

I have a question about this power module

Previously this unit was repaired so i am not aware of this little detail.

The transistores are directly mounted to the heatsink without an insulation between them. However the heatsink is
attached against the PCB with insulated screws so there is no electrical connection between the PCB and the heatsink itself

Does anyone know how the original transistores were mounted in the factory?

Thanks in advance.

It might seem a silly question but i'd rather ask than assume.

[The Dude]

And the heat sink does not bolt to the chassis in any fashion? If that is the case, and the heat sink is totally isolated, I would suspect that isolation is not necessary on the transistors themselves. The schematic won't normally go into mounting detail, but if you have the schematic, you should be able to determine if contact is being made where it shouldn't be.

[g1]

If the heatsink is fully floating (insulated from chassis and circuit board), then this may be the way it was done at the factory.
There are some newer model solid state marshalls that have the output IC metal tab connected directly to the heatsink with no insulator. But the heatsink is insulated from the chassis, so it doesn't matter.

In your case, the heatsink will be at the same voltage as the transistors collectors. As long as the heatsink doesn't connect to anything else there is no problem. The heatsink itself may even be providing the connection between the collectors of the transistors.
However, usually there are 2 types of complimentary transistors in an output stage. So you would need 2 separate heatsinks for the 2 types.
Are all the transistors on your heatsink the same type?

[Enzo]

Or the NPN and PNP roles are reversed, making the collectors the common element.

[MarkusBass]

I don't know about this model but I've seen this in other TE amps. The heatsinks are fully isolated (from the ground) and there is +/-70 V on each of them. You have to be careful and not to touch them when fixing the amp.

Mark

[J M Fahey]

Not in these amps, but some others ground all collectors so do not use insulators and heatsinks are also grounded (think QSC and some Peaveys) and speaker out "hot" is the midpoint of the main filter caps.
To boot, +/-V rails dance following audio.
On first sight, very confusing, until it clicks

[Jazz P Bass]

Here is the GP7 schematic.

There are two available output sections.
A MosFet & a BiPolar.

Either way the + & - rails are on the heatsink.

I would have to assume (hope) that there are in fact two separate heatsinks.

By isolating the sinks & attaching the output devices directly to the sink, there is a better transfer of the developed heat.

[g1]

The parts list shows 2 heatsinks, so I guess each is at one of the supply voltages, as MarkusBass mentioned.

[Lee_ranaldo]

In fact there are 2 separate heatsinks. The circuit has been modified . I'll post my findings here.