Re: QCX Mini 40M smoked #qcxmini #rip

Paul Christensen

To me, it seems dangerous to bring active circuit voltages (i.e., PTT jack) directly to the outside world without some form of buffering.  Even some amount of series R often helps. 


Has anyone added a logic converter/buffer in front of the PTT jack to simply “ground on TX?”  For example, a 10K resistor from the TX line to the (G)ate of a SMD 2N7000 (or equiv.) provides a Vdss max open key line voltage of 60 VDC.  Max current = 200 mA that will safely key any modern external amplifier.  2N7000 (S)ource to circuit GND, (D)rain to the PTT jack “tip.”   I know someone recently made a post about a mod to the QRP Labs 50W amp, but IMHO the mod really belongs inside the QCX Mini. 


It may be possible to Dremel the trace around the PTT jack and solder the 2N7000 (D)rain to the tip lead.  This forms the mounting of the 2N7000 right at the PTT jack.   Short Kynar wire to the other leads. 


Perhaps the next QCX Mini board revision can include the two parts? 


Paul, W9AC       


From: <> On Behalf Of Steve Greffe - VE3SGV
Sent: Thursday, December 9, 2021 8:57 AM
Subject: Re: [QRPLabs] QCX Mini 40M smoked #qcxmini #rip


Yup, shorting out the PTT line claimed my 80M Mini too.
But for me it was hot plugging the PTT to the companion 50W amp. Toasted the Ver. 1 regulator and pretty much everything else on the board that was black and had more than two leads. I'm not equipped to do SMD so it was most economical to start over with a new kit, minus the case. Live and learn as they say. Sorry to hear of the magic smoke experiment you had, but don't feel bad--it's easily done and we're not the first.

Steve VE3SGV 

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