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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 16th Feb 2021, 9:10 am   #1
Denis G4DWC
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Default BNOS LPM144-180-10RF RF Power Amplifier Problem.

An elderly Amateur radio friend has a BNOS LPM144-180-10RF Amplifier. As far as he is aware this is the 180W version of the more common 100W unit.

As an RF amplifier it works OK but he needs to disable the internal VOX as he has a sequencer to make sure the masthead GASFET receive Amplifier is safe before showing it 180W!.

He can't see any obvious way of disabling the VOX facility. It would of course be possible to trace out the circuit out but the tracks are on the underside of the PCB and would require removal of the expensive RF devices which, understandably, he's reluctant to do.

Does anyone have a circuit diagram of other details that would help.

Thanks

Denis
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Old 16th Feb 2021, 9:23 am   #2
Terry_VK5TM
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Default Re: BNOS LPM144-180-10RF RF Power Amplifier Problem.

There's a schematic of the 100W version here, hopefully the RF switching circuit is the same
https://www.george-smart.co.uk/wordp..._Schematic.png
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Old 16th Feb 2021, 10:45 am   #3
Steve G4WCS
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Default Re: BNOS LPM144-180-10RF RF Power Amplifier Problem.

The amp can be hard switched bia a 0v ptt on a jack socket on the rear. Presumably inserting a jack socket disables the rf switching

http://www.staffordengineeringsystem...3-100%20OI.pdf
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Old 17th Feb 2021, 10:46 am   #4
Denis G4DWC
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Default Re: BNOS LPM144-180-10RF RF Power Amplifier Problem.

Hi Terry and Steve

Thanks you so much for the information which I passed on yesterday.

The PTT Jack socket is only a two pole component and doesn't disable the VOX arrangement as would have been sensible. However, my friend now armed with the circuit managed to clip one end of a diode, I didn't catch which one, and it apparently works now exactly as he'd hoped using his sequencer and the PTT input.

Thanks once again for taking the time to reply. You've both been very helpful.

Regards

Denis
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Old 17th Feb 2021, 10:54 am   #5
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Default Re: BNOS LPM144-180-10RF RF Power Amplifier Problem.

Cheers Denis, glad your friend finally has it working as he wants.
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