Keyer use with vintage transmitter

Discussion in '"Boat Anchor" & Classic Equipment' started by KD2RON, Oct 11, 2015.

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  1. K5UOS

    K5UOS Ham Member QRZ Page

    I posted this about 10 years ago:

    For 20+ years I have safely keyed my low power tube transmitters with FET switches like IRF510's. I rebuilt a HAM KEY keyer and added an IRF 510 FET switch, a PNP switch, 9Volt battery and a small pot as a voltage divider. Actually 2 separate circuits.

    The PNP switch key down (grounding the base) applies 5 volts (voltage divided from +9V y the pot) to the gate of the IRF510 and subsequently grounds the cathode of the TX. You need to understand solid state switches but it is a pretty straight forward system common in solid state design. It works particularly well with old 6AG7/6L6 MOPA designs.

    Since keying the PNP switch merely involves a simple isolated switch circuit and grounding the base of the PNP transistor there is no voltage across the key and allows the use of cheap solid state keyers. The current drain from the battery is very little and the battery will last over a year.

    In my big rigs I use the 5 volt winding on the power transformer, bridge rectify, filter and 3 terminal regulate it to 5 volts. I use the same PNP transistor circuit to apply 5 volts to the gate of an IRF730 on key down. There is a variety of MosFET switches for larger voltage and current. Look for lowest Rds (on).

    I key shape it somewhat. A little extra work but safer. I sequence these with a couple of homebrew tube VFO's used with my TX's. The VFO's both have a similar SS switches in an offset circuit that allows the VFO to run continuously. Key down, another PNP switch applies 5 volts to bias a 1N914 diode in series with a fixed cap in the tank that shifts the VFO 10KHz downward nano seconds before the PA transmits. This prevents having to listen to your VFO on receive and allows QSK.

    A lot of the older hollow state VFO's could benefit from a modern SS offset circuit.


    This clever VXO circuit has a similar MosFET switch as part of the circuit. tubevxo/nb6mvxo.htm
  2. N2EY

    N2EY Ham Member QRZ Page

    google "keyall jackson harbor press"
  3. KC0DX

    KC0DX Ham Member QRZ Page

    I have several reed relays in the junk box and would like to learn how to wire one to my solid state keyer that keys all my homebrew solid state rigs. I want to use the keyer for an old Knight T-150 cathode keyed xmtr. Do you have a schematic that can show me how to add the reed relay to the keyer circuit that I already have? Thanks for your help.

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