This was one of those impulse purchases, you know the ones, you lusted after something when you were first licensed (15 years old in my case), but couldn’t quite justify the expense? Well due to sad circumstances one of these extremely rare blasts from the past appeared on the club web site, one of our club members had sent his last transmission and was now SK. Long story short, sealed bid auction, I won it and became the proud owner of this heavy and rather nice looking 80’s 2m amp.

There are many 30w and 100w versions in circulation, but the 200w amp is a rare beast indeed. Anyway, after hooking it up to the shack psu and turning it on, all the lights went out, not just the amp, the entire house!

Not a well amp.

Information on this version – V1 as far as I can find out, is scarce, it is a 25w input, 200w out solid state PA for 2m, current draw is going to be 40A plus I would guess. Internet searches turned up a circuit diagram of sorts and provided a place to start.

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Feet in the air and bottom cover off – Sick MML200

Starting at the power leads (which were in pretty poor condition), the multi meter confirmed dead short across the leads. The circuit diagram was showing an idiot diode across the input, and as the PCB is old school, it took no finding. The multi meter again confirmed that the reverse polarity diode appeared to be short circuit. To be sure, one leg was lifted, and the diode checked again, both polarities. It was toast, short in both directions.

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Reverse polarity diode – one leg lifted for checking

Luckily the junk box had a spare 1N4007, the offending article was replaced, and an ohm meter test now displayed several Meg-ohms across the input.

Power was applied again, and with the current throttle set to 3A the beast was switched on. The relays fired and the amp burst into life. Setting the mode to FM, connecting a dummy load and power meter, and giving the input a squirt of RF from an FT70, the meter deflected over to 10w, an expected output for 1w input. Increasing the drive to 5w gave 50w. The FT70 was swapped for a wouxun 2m giving 7w out, the amp gave a solid 70w.

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70w out for 7w in

The power supply was starting to complain at this level due to current draw, but in all, I am feeling pretty confident that the amp will get close to the 200w with enough drive and current availability. Next tests will be spectral purity with the spectrum analyser, and then on the air to see what it is capable of once the big psu (60A) is retrieved from storage.

In summing up, I always wanted one of these back in the mid 80s, and for the price paid for it from the SK sale, very pleased that the repair cost less than 12p and 30 minutes to sort out.

Beam North and see if you can hear me on 2m SSB