At the meeting of the LRS on 23rd November 2016 Malcolm Hamilton GM3TAL talked about ‘Valves, Tubes and Bottles’, and invited members to tell of their own favourite valves.
The development of the thermionic valve drove the advance of radio and electronics in the last century. Despite the stunning achievements of silicon device technology, valves are still the preferred solution for some challenging applications in amateur and professional radio systems, especially in transmitters.
LRS Secretary, Mike MM0MLB, introduced Malcolm.
A selection of valves brought to the meeting.
Visitor Ian Lindsay GM8LYQ.
His valve is possibly a 6146 HF tetrode power amplifier.
Brian GM8BJF with a 2C39A tripler.
Peter GM4DTH with a QQVO3-10 VHF double-tetrode.
He also likes its big brother the QQVO6-40A.
Alan’s favourite valves were the Mullard QQVO3-20A and (like Peter GM4DTH above) QQVO6-40A double tetrodes which were used for push-pull VHF / UHF PA’s back in the 1960s.
There is a 6-40A at the rear of the photo above.
The 813 was used as a full-power (150W DC input) PA for AM transmitters in the 1950s and 60s,
using a very high (3000V) anode voltage and usually ‘plate (anode) – and screen’ modulation.
A Russian GI7B tube brought by Malcolm.
“Probably one of the better things that came out of the Soviet Union during the cold war, this valve provides a straightforward way to produce 400 watts without too much trouble with “only” 1500 volts on the anode. There are plenty of amplifier designs that use a pair of Gi7Bs to make a kilowatt. Most of the Russian websites claim that the original design and its mil spec ruggedized tropical version were very conservatively rated, so its quite hard to destroy them unless you do something very silly indeed”.