Mitsubishi Power Amplifier modules

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Re: Mitsubishi Power Amplifier modules

Post by radiogareth » Sun Jun 02, 2024 9:11 am

After a mysterious fault in my 70MHz module I took the lid off and was greeted with lots of copper dust floating around inside, in amongst the gold multiple mosfet wires. But then I did use a belt sander to do the flattening. There are other solutions documented somewhere about NOT doing that. TBH using a MRF100 or MRF300 is the easiest route to gain and power up to 145MHz, it all depends on how much power above that I suppose. As an incredibly hand pre-driver I use the obsolete CA2832 module (over 1W out @ 35dB gain, 0-200MHz) and for 70cms, a CA901, not quite as lively but adequate for what I needed. Others available....
The bricks are/were a handy solution......

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Re: Mitsubishi Power Amplifier modules

Post by g6hfs » Sun Jun 02, 2024 9:32 am


Thanks, but not sure I could do that type of buiding now with my condition, pcb would help make it a lot easier.


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Re: Mitsubishi Power Amplifier modules

Post by G3GJA » Sun Jun 02, 2024 11:04 pm

Every failed RA18H1213G module I have encountered has had a sanded flange. The last one came out of GB3EY where it was used as a driver at only 0.5W out and the gain jumped with temperature. It was purchased from PE1RKI.

Mitsubishi went to a lot of trouble and cost putting the indent into the flange, so it's reasonable to assume that it is required for reliable operation. The gap between the flange and the heatsink is only 0.09mm, which is not significant for heat transfer if a good thermal compound is used. The gap allows spreading of the compound to prevent stress on the flange.

The datasheet gives full details of how to mount the device. There's no mention of sanding the flange.

In my view, the information given on the Down East Microwave page is wrong and is probably responsible for a lot of module failures.

Clive G3GJA
Last edited by G3GJA on Mon Jun 03, 2024 4:19 pm, edited 1 time in total.

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Re: Mitsubishi Power Amplifier modules

Post by g4saq » Mon Jun 03, 2024 12:51 pm

I agree that the advice to sand these devices is highly questionable. Mitsubishi know what they're doing and made the flanges concave for a reason. I am attaching the Mitsubishi mounting instructions. The 23cms module now sells for over £100 (only a few left), so it's worth looking after them.
Like others, I mounted mine in a Hammond die cast box but instead of fixing the module to the Hammond, I cut an aperture in the box and placed a piece of 3mm copper heat spreader on the outside, between the box and the heatsink. The module is screwed down directly onto the copper. There is a lot of good advice about ensuring a good ground connection. I followed GM3SEK's advice to run wide copper strips from under the heads of the mounting screws to the top surface of the PCB.
External PA.jpg
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Internal PA.jpg
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Mitsubishi mounting instructions.pdf
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Re: Mitsubishi Power Amplifier modules

Post by SkyVision » Tue Jun 04, 2024 1:11 pm

This is a great topic and I'd love to hear what you think and what heat sink compound you use and like
I'm glad you raised the mounting instructions, generally I would agree, but after 20 years of fixing two-way radios I'm synical
The sad reality is the Kenwoods/Simocos/Taits/GMEs with indent modules never look all that great, lucky the modules are tough
The pics are random radios with indent modules, air bubbles, poorly applied compound, solid/dried out compound or way too much

-Not many bother to follow the instructions, even the big brands struggle, so what hope have we got :D
-The quality of the heat sink compound is questionable (the tube we got on special 10 years ago)
-Even good quality heat sink compound is compromised with age and heat, the oil seperates and runs away
-Air bubbles seem to be normal without great care (just like putting a plastic screen on a phone)

I like Dow Corning Heat Sink Compound, but our tube in the workshop, the oil is seperating from the paste in the tube, imagine in 10 years
A larger amount with air gaps on the side of the module with heat from added bias, has more chance to ozze and dry out
LDMOS uses no such indent, so I doubt this practice has much scientific backing, just two flat surfaces with a smear of compound
Personally I use a pallet knife or scrapper to apply a thin consistant coating to both surfaces, depress one side first, slight rotating motion

Less is more in my humble view Roger VK5YYY
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Re: Mitsubishi Power Amplifier modules

Post by g4saq » Tue Jun 04, 2024 2:02 pm

Hi Roger,
Well, it sounds like you have vastly more experience than me with these devices (and in general). I sifted through as many references as I could find before embarking on construction. The consistent message was that these devices get hot and that managing temperature rise is vital. I have been surprised by how inefficient the modules are when biased at 5V for class A. My 60W UHF module draws over 12Amps. The 23cms, 18W module, whilst drawing less current, is even worse. With my mounting method, at full output, the VHF/UHF modules don't get hotter than 30 C. The 23cms stays at about 42 C. That is on a smaller heatsink but still with a fan.
As for heatsink compound, I bought a small tube of fancy computer stuff (?? Arctic Silver) for the VHF module but used plain old Dow Corning for the UHF and 23 cms modules. I also used a thin layer of Dow Corning between my copper spreader and the aluminium heatsinks. One thing I have noticed is that the heatsinks get hotter than the top of the module cases, which I take to be a good thing.
GM3SEK suggested (having applied compound), "Place the module onto the heatsink so that one long edge touches first, and then lay the module down onto the heatsink like closing a book. Hopefully this will avoid any trapped air bubbles. Give the module a small shuffle to help spread the conductive compound and expel any trapped air." That sounded well-considered advice, which I followed.
73, Russ.

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Re: Mitsubishi Power Amplifier modules

Post by radiogareth » Tue Jun 11, 2024 3:59 pm

Well the little module arrived today, professionally packed with desiccant, humidity indicating card, anti-static bag and very well packed in a stout box. I can confirm that it does indeed deliver the stated gain and with excellent linearity too.
At 28V I'm getting 2.5W with shoulders at -40dB. Pluto set to around -14dB for this. It will go to 4W but the shoulders are then around -25dB.
It fully drives my modified G4BAO (with upgraded transistor) with the added benefit that it also runs off 28V. It made the RG58 warm, so its working ;-)
If you want one remember to make an offer but I also have a direct email now which might give better prices, but outside eBay of course.

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Re: Mitsubishi Power Amplifier modules

Post by g0mjw » Wed Jun 12, 2024 2:48 am

Hi Gareth,

Interesting. The shoulders need to be -50dB or more on 2m/4m if they stray out of the band. I could only get them that low with one of Rob's PAs on 2m. I have not tried on 4m with the brick but my 500W LDMOS PA biased up would do over 10W. No need for any more with the EIRP limits. Of course, the EIRP limit doesn't apply if you are within the amateur band and not the extension. This is tricky with higher SR but entirely possible with low SR we might need to send a contest exchange. So, your 4W might be usable, though not especially neighbourly, well inside the bands.

Incidentally, on 70cm I can get 5W out of the 60W RA module and on 23cm I can get 3W out of the 18W RA module, but not quite as clean on 23cm. The penalty is needing 5V on the bias pin and consequently very low efficiency and need for a large heatsink.


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Re: Mitsubishi Power Amplifier modules

Post by radiogareth » Wed Jun 12, 2024 6:24 am

Mike, The module in question is for 1250MHz, although the PA device is nominally rated to 1900MHz there was a rapid falling off of gain near there and beyond. But I needed a 'single' driver between the Pluto and the G4BAO amp which this does admirably. Now to wrap it all up with changeover relays and a hot preamp.
Noted on your other figures, I only have a brick for 23 and yes, thats flat out and biased up to the eyeballs for not much RF. The BAO amp (with the uprated PA device) is far superior taking a max of 4 amps at 28V and showing 40+W out after warming 2m of RG58.

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Re: Mitsubishi Power Amplifier modules

Post by SkyVision » Wed Jun 12, 2024 2:12 pm

Great news Gareth

I've been running the xihu888 23cm module on 21-20V from an 18V 5A/hr Milwaukee tool battery, with the view to use portable
Had about 3 hours of useage @ 1W DVB-T wideband with a small voltage converter also supplying the modulator and upconverter
Power started to decrease after 3hrs but still usable below 18V, heatsink barely gets warm
I ordered 2 and got him down to $48US each, considering it's in a nice housing, just add power and heatsink, it's great value

A friend is buying his 13cm version to see what that's like

Cheers Roger VK5YYY

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