Thoughts on crystal substitutes

[John 4EDX]

Hi All,

Construction of my first Paraset replica is going to plan. I've built a wooden box to hold the mains power supply today (my old woodwork teacher would shoot me if he saw it!) and I wound a new receiver coil yesterday. The dip meter tells me it tunes from below 3.5MHz to 11MHz or so. The coil former is only 21.5mm diameter so I used an online solenoid calculator to scale the number of turns.

I've made an adaptor for FT-243 crystals and I have two, on 7.010MHz and 7.025MHz. Some of you might find the following suggestion unforgivable (!) but I'm wondering whether one of the tiny digital oscillators (DDS or PLL) might be used instead of a crystal, plugged into the crystal socket and powered by its own battery. I think the twisted wire around the anode lead would have to be disconnected. Any thoughts on this? When my Paraset is built and working I'll do some experiments.

73,

John 4EDX

[Parasetguy]

Hi John

I vaguely remember having seen a photo of someone using a DDS in stead of a xtal.
Check if there is any DC and AC (HF!) voltage between pin 5 and ground when key up and key down.
The voltage chart I have gives no clue about that.
Depending on the results of your measurement you can decide if it is safe to connect the DDS.

The twisted wire gives a little AC feedback, like a microphone in front of its own loudspeaker. It helps the tube to oscillate. Removing it might prevent that.

Kind regards,
Henk - Parasetguy

[John 4EDX]

Thank you Henk,

I still haven't found my 6V6 so I'm a little way away from trying this. It occurred to me that the DDS or PLL "crystal" will provide a netting signal for the receiver so will need to be switched off manually during reception.

73,

John 4EDX

[Parasetguy]

Well. maybe an extra contact on the receive-send switch can disconnect the xtal socket?
Or is it the radiation of the DDS that worries you?

Kind regards,
Henk - Parasetguy