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Old crystals are very large compared to present day devices. Vintage transmitter circuits did not have many valves in their line up.

I have seen a 2 valve 50 watt CW transmitter for 80 meters in a 1950s electronics magazine. When transistors arrived RF types were more expensive than the valves they replaced, so in the 1960s the number of transistors in the transmitter strip was kept to a minimum.

The transistors had less power gain than the valves, but it was normal to make a 5watt HF CW transmitter with only 2 transistors. The crystal oscillator in these cases is called upon to deliver significant power.

Surely the crystal drive power must be quite high.

Would new small crystals have a short life in these old circuits?

Would the frequency stability be bad when present day easy to find small crystals are used?

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  • \$\begingroup\$ It's really down to the detail (not provided). Example circuits and data sheets are needed. \$\endgroup\$
    – Andy aka
    Dec 22, 2018 at 11:03

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Power handling ability of a crystal seems to be directly related to size. The dissipation is related to the ESR though.

Small SMT crystals might be 100uW-500uW max. HC-49 crystals can handle around 1mW. Some older crystals can handle as much as 10mW.

See this 1972 crystal catalog.

Here is a chart from that document showing the typical drive power vs plate voltage:

enter image description here

Overdriving a crystal can lead to premature aging and even failure.

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    \$\begingroup\$ Amateur radio applications often push the parts harder than they would be in continuous commercial service, and so would wear out sooner. There's even a term for it in the older literature -- intermittent commercial amateur service (ICAS), if I remember correctly. So even if you use the crystals called out in the designs, don't be surprised if they die early deaths. You may want to sneak in a transistor oscillator, or use a low-level tube oscillator (some 7-pin pentode stage) ahead of the "oscillator" stage. \$\endgroup\$
    – TimWescott
    Dec 22, 2018 at 17:08
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    \$\begingroup\$ @TimWescott good point. The ARRL Handbook probably has some good info. \$\endgroup\$ Dec 22, 2018 at 18:22
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    \$\begingroup\$ Good 1972 catalog .+1 . \$\endgroup\$
    – Autistic
    Dec 22, 2018 at 21:12

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