QRP 50C5 valve transmitter (W5LET design)
A good design for low parts-count valve xtal controlled QRP transmitter (CW) can be seen at:
50C5 Euro QRP transmitter from Mike WU2D
This design is "elegantly simple" and acheives the maximum performance with very few components.
The mains transformer has been omitted with all operating voltages being derived; directly from the 230V AC mains supply.
An alternative to using a voltage dropping resistance in order to supply the 50 volt tube filament,
is to use a capacitive divider as shown/explained below.
While both methods will work, the capacitor uses no power (heat),
and also, a 2 uF (motor start/run) cap' may be easier to source than high wattage resistors.
The Capacitor must be non-polarised and at least 250 Volt AC rating
Readily available motor start capacitors will suit the requirement.
I have had occasion to use the "capacitor voltage-dropper idea" and find it works OK.
Another good suggestion (in comments) (untried by myself) was to include a series diode in the filament supply,
which could also help to "break-down" the supply voltage level!