Missed it by that much

A customer emailed about keying an FT-101EE with a stock PK-4 keyer kit (no SSR) that he had purchased.  Looking at the FT-101EE schematic it seemed like there was no typical cathode (positive) OR grid block (negative) high voltage involved.  So I mentioned that the keying voltage and current should be measured first but that it looked like it might work without the SSR.

BZZZZZT !

After building the PK-4 the customer emailed and said that while the measured keying voltage (11.3 volts) and keying current (6.5 mA) were relatively low, the PK-4 caused a key down condition when hooked up.  The PK-4 output transistor tested OK with an ohmmeter.  

Unfortunately even though the voltage and current were low, the voltage polarity was negative.  Digital volt meter strikes again !  It can be easy to miss that little negative sign on the display.  An analog VOM will pin (sometimes audibly) with a negative voltage or current.  The negative voltage is a problem because there is an inherent diode between the drain (cathode) and source (anode) of the 2n7000 MOSFET output transistor.

The giveaway was that the customer's MFJ-401D keyer worked fine with the FT-101EE with the output jumpered for grid-block (negative high voltage) keying.

The PK-4 SSR option would have been the easy way to go, it was needed even though the voltage and current involved was low.  The SSR I sell with the kits now is an IXYS part:  CPC1593G   It is a 600V, 120 mA, 6 pin solid state relay available from Digi-key or Mouser (yes they are cheaper than Jackson Harbor Press ;).

The customer is buying the CPC1593FG SSR from Digi-key.   

(UPDATE 7-30-2023: the customer reported that the SSR was received and is now at work keying the Yaesu FT-101EE)

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm