Crystals (FT-243) in a novice transmitter - help.

Discussion in '"Boat Anchor" & Classic Equipment' started by K9UR, Nov 10, 2021.

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  1. K9UR

    K9UR Subscriber QRZ Page

    I bought 4 crystals from ebay... they are "modern crystals inside a FT-243' holder.

    They disappointingly sound awful in my boat anchor. Chirp and whoop whoop...

    It's not the transmitter- as an original pressurized crystal works great and sounds great but it's too far up the band and is on a digital frequency.

    What if any are my options -- can I do something to reduce the chirp using the crystals that I bought ? Or do I need to find original pressurized crystals for the low end of the 40M band ?
     
    Last edited: Nov 10, 2021
  2. SM0AOM

    SM0AOM Ham Member QRZ Page

    You could redesign the oscillator to a circuit which has lower crystal loading.

    The Grid-Plate or Modified Pierce circuits are among the better.

    73/
    Karl-Arne
    SM0AOM
     
  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Sometime in the last several months there was a discussion about adding a resistor to reduce the voltage being applied to the crystal. The old crystals were physically larger and operated with much higher voltage that can damage the smaller crystals.

    Suggest you do a little searching for that discussion.
     
    K9UR likes this.
  4. KP4SX

    KP4SX Premium Subscriber QRZ Page

    G0CIQ, K9UR, W7UUU and 1 other person like this.
  5. W9BRD

    W9BRD Ham Member QRZ Page

    https://www.qsl.net/wb1gfh/ameco1.html

    May improve note with HC-49s, but likely not make them sound modern. They're too physically small.
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    What's the transmitter? Or if homebrew, what's the circuit?

    Some old Novice-level TXs are just "power oscillators" and have no buffering or PA, just a tube running several Watts in a powerful oscillator. Those are hard on crystals, but can often be modified.
     
  7. K9UR

    K9UR Subscriber QRZ Page

    knight kit T-60;
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I had one of those! But I didn't build it, I bought it used.

    Folks used to modify the 6HF8 circuit (main oscillator) to accommodate lower activity crystals. I'll see if I can find something on that. It's been a really long time.
     
  9. K9UR

    K9UR Subscriber QRZ Page

    ya, this is just a fun project. I got bored of running the weekly cwt with my fancy icom 7610....thought i might try with a novice setup. T-60 at around 22W output, Drake 2B/2BQ and johnson T/R box for full break in. Crystal controlled...of course....
     
    KA5IPF likes this.
  10. WA5VGO

    WA5VGO Ham Member QRZ Page

    I don’t think voltage has anything to do with it. The issue is current. The tiny modern crystals simply can’t handle the crystal current present in most of the old vintage transmitters. If you continue to use them, they’ll likely fracture. There are solutions for using them, but the best solutions are to either find genuine FT-243 crystals or use a VFO.

    Darrell
     

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