NAD 3130 conversion to Lateral FET

[poundy]

So im making a start on this as the 3020 i did was realy succesful

Bit more difficult with this one as there is no provision on the board for the TO-247 pattern, so im going to have to be creative

The circuits are very simlar in most ways to the 3020 so it should be straight forward in that sense, but not so in other ways

will progress updates as i go along 👍

 

[poundy]

so i will elongate the heatsink to facilitate the legs of the transistors

plenty of room and scope to improve the heatsink

 

[poundy]

so the old heatsink is out and modified-ready to clean and have a light spray

i will clean up, re cap and prepare the board while it is out-the burned area components are actualy ok, must be an old scorch mark

never seen these installed in a 3130 before

 

[Mooly]

Those are quite a high powered device, 150 watt, 80volt vce but slow by modern standards. Bit like an uprated 2N3055. Worth saving if they are OK.

 

[poundy]

so all cleaned up, and re capped, only took an hour using the hakko

now almost ready to do the buisness end

new mains lead and converted to mains earth

 

[Mooly]

Looking good. Some new caps in there I think. That 2043 opamp might be worth a play when its all done 🙂

 

[poundy]

so have a look at this, first pic all cleaned up, it was rotten, and no issues

but what about the other one, no wonder that circuit was burning

 

[poundy]

Looking good. Some new caps in there I think. That 2043 opamp might be worth a play when its all done 🙂

complete electrolytic recap. might as well while im doing this amount to the amp

what would you do with the op amp then?

 

[Mooly]

Those look like knife cuts across the print to me

 

[Mooly]

what would you do with the op amp then?

Knowing how you like to experiment with these things it might be worth trying something different (the 2043 is like a 4558 which isn't particularly great even though it is very common) but I see the supplies to it are in typical NAD fashion a bit weird. Nothing that can't be solved easily though. Maybe something like a an OPA2134

 

[poundy]

well im up for trying things

as it happens i wanted to do this one without the VBE and drivers

it should work as it is very simplar to the 3020 we did

 

[poundy]

Those look like knife cuts across the print to me

they do look like it, but to what end, not to seperate the print as the far righ one still has continuity
oh well they need to be repaired so thats the next job i think

 

[Mooly]

as it happens i wanted to do this one without the VBE and drivers

We did a sim of the one with no drivers:

I would get it to work first with the multiplier, then think of removing that if you want. Ideally we fit a fixed resistor in its place because the current might be a bit high to feed into a preset wiper.

they do look like it, but to what end,

They definitely look like deliberate cuts to me. Scrape the lacquer and bridge with a cm or so of wire.

 

[poundy]

ok so keep the quasi pair ,ditch both the drivers, fit a 2K pre set and loose R459
i can see what your doing here, i think it should be easy enough, just a few links

 

[poundy]

now this didnt work out bad at all-for info i used an old heatsink from a 3240PE

so start planning fitting the FETS

 

[poundy]

dry fit first N channel see how it sits, quite nicely as it happens, the board side is the tricky bit and i learned alot doing that first one, so this should be alot neater

 

[poundy]

so with the VBE still fitted, i will leave the 1 ohm in place so i have somewhere to measure from

just check i have this correct

 

[RS232]

Nice project but paint on the heatsink on the contact surface of the mosfet ?
Doesn't it reduce the heat transfer ?
Just asking out of curiosity.

 

[Mooly]

just check i have this correct

That looks correct. Remember the multiplier has to be set to give minimal voltage between the gates. Do as we did on the one you have already done, and I can't remember what val;ue preset you used for RX1 but around 2k sounds in the right ballpark so perhaps a 2k2 or 4k7 preset for RX1.

If you use the bulb then provided the FET's are fitted correctly they will be safe.

 

[poundy]

Nice project but paint on the heatsink on the contact surface of the mosfet ?
Doesn't it reduce the heat transfer ?
Just asking out of curiosity.

the paint is very thin, but it is metal flake paint so it conducts realy well, but you are right, if it is too thick it would have an affect, not sure how much though