PF-HC-3F

This tube was designed by H. J. Round and made by Ediswan for the Marconi Wireless Telegraph Co Ltd (GB). Most transmitting types had three filaments of lime coated platinum wire, with the provision fo use them singly, if required. Some valves had 4 contacts. in the base sheathing. These bases were usually nickel plated brass. Properly used, these valves achieved amazing sensitivity and performance.

Some valves had a tubulation on the top mwhich contained amalgam instead of the usual asbestos. This was a method of adjusting the vacuum