Mitsubishi RA18H1213G Module

[Nick]

I'm building a 23cm amp using the RA18H1213G module and noted that the heat spreader has an indentation of 0.09mm in it.

Not much, but most of the base will not be in contact with the heat sink when it is bolted down. I've built amps for 2mtrs and 70cms using the Mitsubishi 60W amplifiers and these don't have this indentation.

I have no idea why this has been done on this module as it seems a bad idea for aiding heat dissipation, but there must be some reason for it. The amplifier for 70Mhz also has this indentation.

I'm thinking of attempting to lap the base with wet and dry paper to make it flat if possible without breaking off the leads.

Is it worth doing this or should I just leave it as it is ?

Regards,

Nick - G4NKV

[g8vpg]

Nick,
If you have not already done so, I recommend you read GM3SEK's paper on using these modules;
www.g4ddk.com/AN4.pdf
I used a belt sander to level the base of these modules. This does the job quickly and well, but does generate a lot of friction heat, so must be done in stages. The underlying metal under the plating is copper. I wouldn't use a wet process, because if water got through the sealing around the plastic cap, it would cause real trouble.
73 Shaun.

[G4FRE]

you might want to read the findings of Steve, of downeastmicrowave at http://01895fa.netsolhost.com/PDF/MOSFET%20PA_pdf.PDF
my modules have all been sanded flat

Dave
G4FRE

I'm building a 23cm amp using the RA18H1213G module and noted that the heat spreader has an indentation of 0.09mm in it.

Not much, but most of the base will not be in contact with the heat sink when it is bolted down. I've built amps for 2mtrs and 70cms using the Mitsubishi 60W amplifiers and these don't have this indentation.

I have no idea why this has been done on this module as it seems a bad idea for aiding heat dissipation, but there must be some reason for it. The amplifier for 70Mhz also has this indentation.

I'm thinking of attempting to lap the base with wet and dry paper to make it flat if possible without breaking off the leads.

Is it worth doing this or should I just leave it as it is ?

Regards,

Nick - G4NKV

[Nick]

Sanded flat as has been suggested - took me two evenings doing by hand on the desk. To ensure a good thermal and electrical contact with the heat sink I used MG Chemicals Silver Conductive Grease (RS 124-7683).

Seems to work OK - I can get 20-22W out from it before it saturates. The documents above seem to suggest they obtained more, but it does work above rated specs so all OK. Do need to install the fan - the temperature went above 50 C on testing.

[M0DHP]

Hi Nick

I'm building an amp with one of these modules soon. What heatsink are you using?

73
Ray M0DHP

[g0mjw]

A large one. Bigger the better as it needs to dissipate upwards of 60W. for long periods in DATV use. The purple heatsink that comes with stealth Microwave amplifiers is about the size you would need. The SM3437-25L amplifiers were going for £5 each towards the end of their availability. I am using an old BNOS 25W amplifier chassis but that needs a fan.

You can also use a smaller heatsink with a blower, e.g. a CPU heatsink.

Mike

[Nick]

Hi Ray,

The heatsink is from RS - part 169-4252 - see attached photos.

It does not have the fan fitted yet, but this will be done the same way as the on on my 2Mtr amp - see photo.

I have fitted a temperature indicator/controller on these amplifiers - you can see the temperature sensor on the internal view of the amplifier just above the RF module (it's a mess at the moment as the RF switching relays are not yet fitted). The temperature controller is mounted on the front panel - this was obtained from E-Bay.

I have set the fan to run at low speed all the time, and to only go to full speed if the temperature goes above 45 C. So far, on the 2Mtr version, it has not had to go to full speed.

Nick -G4NKV