elektronka 8438 = QB4/1100GA = CV3879 = 4-400A Beam Power Tube EIMAC

Nova nerazpakovana lampa 4-400A EIMAC.


4-400A/8438
EIMAC had been working on their new tetrode line through most of WWII with their 4-
125A and 4-250A tubes. These were a big success. They wanted to go bigger so they
introduced the much larger 4-750A in 1946. They quickly discovered that with a better
designed plate structure, they could improve the dissipation. The 4-1000A was the result
in 1947. It was obvious that the same type of structure would work on the 4-250A, so the
4-400A was introduced in 1948 with FM broadcast in mind. The 4-400A had the same 5-
volt, 14.5-amp filament as the 4-250A and a maximum voltage of 4000 volts. Both tubes
were capable of 1000 watts output, but the 4-400A did it with a greater margin. They
also introduced the 4-400A/400 Air-System Socket to provide adequate air to the tube
without requiring the chassis to be pressurized. That socket was re-named the SK-400.
If you use a pressurized chassis, the Johnson 122-275 ceramic socket can be used with a
chimney at a big savings.
The 4-400A/8438 was used in several commercial and military amplifiers for several
years. In the 1960s, a zero-bias triode version of this package, the 3-500Z, became
popular in grounded grid amplifiers. The grids of the 4-400A could be tied together and
make it a good alternative to the new expensive tube. At high voltage, both tubes
required some fixed bias, so when an exchange is made, the biasing zener diode needs to
be changed. Surplus 4-400As became in high demand. A version of the 4-400A was
made with the base and pin structure of the 3-500Z and it was designated the 4-400B or
7527