The HK-257-B or 4E27/8001 is a 75 watt dissipation pentode usable for full output to 75 MHz. The HK-257-B differs from the HK-257 only by being .75 inches shorter. Newer versions of the H&K tube had holes in the ceramic base and cooling holes in the skirt. Lewis Electronics made a similar 4E27 as shown in the third example and they also made the AT-257 a similar tube. A different envelope shape was used by Lewis & Kaufman for some of their 4E27s and others were the more traditional as shown in the fourth and fifth examples. The sixth and seventh examples were made by Pacific Electronics, and seem to be identical with the early Lewis tube. The eighth was made by ICE. RCA made tubes with the 4E27/8001 designation as shown in the ninth example.
Length = 6.20" Diameter = 2.75"
Max voltage = 4000
Max current = 150 ma
Fil voltage = 5
Fil current = 7.5 amps