by Norm Wilson N6JV – Visit the museum at N6JV.com
10
In the March, 1921 issue of QST, RCA announced that they had added their first CW power tube to their post war lineup. The UV-202/C-302 had construction that was similar to their others tubes with short pins and a brass base. It was rated at 5 watts output. The first 202 tubes I ever found had their bases removed. This was a common practice to get a tube to operate at higher frequency as it reduced capacity.
In the October, 1925 issue of QST, RCA announced several new tubes including the UX-210/C-210. The new tube was called a 7 ½ watter and it had the new UX base. That base had long pins and was made from baklite plastic. The plate voltage for transmitting was 425 volts at 60 ma. When used as an audio amp in a receiver, 90 to 157 volts could be used. The filament voltage was 7.5 volts in a transmitter and 6 volts in a receiver. The mu was 7.7 which made it a better oscillator then the UV-202 was. By 1929 the ARRL Handbook didn’t list the 202, but almost every transmitter circuit featured a UX-210 as an oscillator or amplifier sometimes using several parallel tubes.
With an effective monopoly on tube production in 1929, RCA was in control. Control was lost in the early 1930’s when the courts broke the game open when they allowed other makers to build tubes using the RCA patents. Soon production was started at Sylvania (210), Raytheon (RK-10), Taylor Tubes and others. RCA made the 10 in a different envelope and designated it a 10Y. It was also known as a VT-25-A and was used as the speech amplifier in the WWII BC-375 transmitter that was incorporated in the B-17 bomber and other mobile and fixed applications.
Today these small triodes are all collector’s items but audio enthusiasts have made a big market for them.
Leave a Reply