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Hello. I had my TMB working perfectly.
I have installed the VRM (scaling the entire amp), but as soon as I switch the standby off, the 0.5A fuse blows..

I have installed the mosfet without any silpad insulator, but with a white heat sink to chassis..
Is that OK?

The 6V diode cathode goes to the drain and the anode goes to the variable output, right?
Diode used: 1N4735A
Mosfet used: IRFPE50
Did not used 1N4007 diodes since I am scaling the whole amp..
THANKS VERY MUCH for any help!

Why are using a 0.5A fuse? Is this the fuse that is in series with the incoming house voltage?

It should be 2A for 120V operation or 1A for 240V operation.


edit: use the continuity function on your DMM and make sure the MOSFET is completely isolated from the chassis. Sounds like it may be shorting to the chassis (ground) as some point due to your isolation method.

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http://pdfelectronics.com

Here we have 220v. I have 2A fuse in mains and added a 0.5A fuse in B+

I think I found the problem:
As I said earlier i did not use a pad but the mosfet directly to chassis only with grease between them.
With the mosfet screwed to the chassis drain was making contact to earth in some cases.
I unscrewed the mosfet and no longer the fuse blows..
How should I attach the mosfet? I cannot find a pad in here.. What material is it?

Question 2: shall I scale the entire amp or just the power tubes? I want to achieve as closest sound as possible compared to having the amp at full volume..
Thanks again.

You need either a Mica pad with silicon grease or a Sil-Pad which we use, to put between the Mosfet and chassis. Amazing that you didnt blow the Mosfet!
We scale the whole amp and people like it.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I found the Mica and put it on like this:
Chassis -> Grease -> Mica -> Grease -> Mosfet..
I like the sound of it, but I now have to test it just scaling the power tubes!

Thanks for the help!

good, now you will need some diodes to split the power supply and you will need to play with the voltage dropping resistors to get the preamp balanced.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

From my experience its not worth the hassle and headache of scaling just the poweramp.

Enjoy your amp now for how it is!

_________________
http://pdfelectronics.com

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps