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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?
From: QRPLabs@groups.io <QRPLabs@groups.io> 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.