PV-12AL hum issue due to shorted transistors

[amplifiersurgery]

Hi Folks, I am restoring a PV-12AL and found a pair of shorted mosfet transistors near the front right side that are mounted together to the same heat sink. The previous owner had put in incorrect transistors that also burnt many zeners down the line. I am unable to find the schematics for a PV-12AL online or through CJ. I would like to request someone out there who has the same unit PV-12AL to let me know what the original part numbers are on these two transistors. Alternatively, if someone has the schematics for the PV-12AL, please do share. I will be very thankful. Regards, Hamad.

[admin]

First, let me welcome you to the site. We should have the PV12 schematic files in our schematics database. viewtopic.php?f=17&t=128

Let us know if this is no good.

[amplifiersurgery]

Thanks for the warm welcome. I had a look at the PV-12 schematic and it is quite different. The PV-12AL has many modifications and I am not even sure if this shorted transistor pair should be a bipolar transistor or a MOSFET. I called CJ today and they mentioned that they did not have any schematics for the PV-12AL. I suspect none were published. If anyone could simply read off the numbers off the first transistor on the front, I think I would be able to figure out the rest. Regards, Hamad

[admin]

I own the PV12AL. I did post some pictures here of the internals: viewtopic.php?f=10&t=40

Any chance that you can see what your looking for?

[amplifiersurgery]

The pair of transistors are to the right of the tubes.
I think one can make out the part numbers on the front transistor and that should be all that's needed.
The one on mine shows IRF710 (which is a MOSFET transistor). I want to confirm that it is the original part.
I have attached a picture showing the transistor pair.

[admin]

It's unfortunate as the picture I have you can almost make out what it says on the transistor. I would hate to take my unit apart as I have other components stacked on it and a bunch of cables connecting to it. I'm thinking, can the faceplate be removed easily so I can open it up and just take a picture from the front?

[amplifiersurgery]

No worries, thanks for responding and for taking a look. I am sure someone else out there will have the same model too. The only way to access the part is by removing the top plate (just like you would if you were changing the tubes).

[admin]

No problem. I'm surprised that CJ doesn't have the schematics for this, I wonder how they do their own repairs? If your completely out of luck, let me know as maybe in the future I can take a look. It kind of sucks as I have my PV12 under my other components so I have to do a bunch of rewiring just to take it out.

[amplifiersurgery]

Folks at CJ told me that their international distributors may have an old schematic that perhaps they could share.
So I am hoping that this forum has some international CJ enthusiasts that can perhaps get a copy of the PV-12AL schematics.

[epiengineer]

Hello, I've been searching for other people with low-volume channel drop out on a PV-12AL and came across this thread. Perhaps it is too late, but my PV-12AL does not have that configuration. Mine is a single transistor on the heat sink, but facing the opposite direction, as shown in the attached photos.