Which can be good and bad:
Good - less susceptible to damage if used without an antenna properly connected
Bad - requires short pause after pressing PTT before transmitter is fully operational; some later batteries do not have 3v connection so can only be used with 77 sets.
The valves are robust and still readily available. Adapters using common D cells are available for both radios.
Howard
Not sure if that is a 25 or a 77 set not much difference but the 25 still has 1 vacuum valve. 
