Does anyone know what IC they use in the amplifier of this probe kit? The P/N of the amp is 7405-907B and goes to 3GHz.
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It is a simple TO-92 metal can, four pins, IN, OUT, V+ and GND. Needless to say there is no lettering on it, bare metal. Just the supply, no inductor like with MMIC. Cap in, cap out, that's it. This amp is used for the hunting of miniscule noise sources.
The batteries croaked and I want to see if it can reliably stomach Li-Ion voltages but don't want to risk bricking it. This would also give me longer run times.
Maybe it's a TO-8 package. First thought was the MWAxxxxx, but those are 3 legged devices. Sounds like a common MMIC. You could put a 12V regulator in front of the battery to protect the amp.
I have the same probe kit, but not the Optional Amp.
Run it temporarily on a supply, crank up slowly while observing current. Anywhere close to breakdown the current will be increasing rapidly. Stop ;-) ...Jim Thompson
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It's what you learn, after you know it all, that counts.
Not a common MMIC because it doesn't have an external emitter resistor and choke.
It ran on four little NiCd batteries so 4.8V. When planting new batteries in there this doesn't leave much space.
It is a nice kit though expensive. The mid-size H-loop is unfortunately gone because I smoked it while diagnosing a susceptibility issues. It didn't like the high transmit power and literally smoked out.
Ok, I can put a limiting resistor in series so it can't go into instant thermal meltdown. However, will that make 100% sure that the amp in the can survives avalanching?
Since the kit is from the early 80's it is possible that this is still an epitaxial Ge-device. Must be well protected internally though because the environment I normally use it in is nasty. Except that after "only"
30 years of service the NiCd batteries leaked out and that small size has become unobtanium. Hurumph.
Can you simply count the number of NiCads and multiply by 1.2V? If the Li-Ion voltage is greater, how about a nice LDO to drop the voltage, or perhaps a diode or two.
... and found that 2/3-AAA almost fits. At least I can make them fit. Only 300mAh but that'll do for most sessions. I found them at Durnergy in Canada and just ordered them.
Thanks to Lasse's hint I found that 2/3*AAA almost fit and they just arrived. They are a tad too short but the battery holders in the EMCO
7405-907B amplifier have hollow-rivet terminals. I took four M-2.5 (metric) flat-head screws, cut them down to about 1/4" total length, slid them into the negative terminal for each battery holder, down the center of the hollow rivet, and inserted the batteries. The flat heads make up for the shorter length of the 2/3*AAA batteries. Now it all works. Make sure the remaining shafts will not stick out because that can short against the enclosure frame.
This company in Canada has the batteries I used:
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They also sell through EBay. Keep in mind that these have a much higher capacity than the old ones so charge times when pretty depleted will be
2-3x of what they used to be. It's also NiMH instead of NiCd.
The charger is way oversized. Mine has 200mA output while the current is
15mA. I could increase the charge current but it doesn't matter to me because the amp easily holds for a whole noise hunt job. Well, now two jobs I guess.
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