12-02-2014, 05:12 PM
I think the reason stems from the USA use of 2.5V for tube heaters back in the early 30's. A line up for a set I'm working on at the moment uses ones that draw 0.8A, 1A and the 2A5 O/P tubes are 1.75A. The O/P valves are in class A and so a beefy rectifier was needed. What else than the 80 which had been in development since the late 20's. Only draw back it needed a big filament and at 2.5V it would have consumed 4A so maybe it was a logical step to say OK double the voltage to 5V and then it only needs 2A (which it does).
I have an article by Peter Lankshear, who knows as much about early radios as anyone out there. In it he traces the history of the 80 all the way to valves like the 5Y3G which was an 80 with an octal base. It seems the 80 was such a successful design it lived on ... why change something that worked and as it was indirectly heated it needed a separate transformer winding anyway so the 5V was no problem.
Its a good article and I will find the time to scan it and add to the thread.
Gary
I have an article by Peter Lankshear, who knows as much about early radios as anyone out there. In it he traces the history of the 80 all the way to valves like the 5Y3G which was an 80 with an octal base. It seems the 80 was such a successful design it lived on ... why change something that worked and as it was indirectly heated it needed a separate transformer winding anyway so the 5V was no problem.
Its a good article and I will find the time to scan it and add to the thread.
Gary
