21. Pentodes are made in two classes : those with the suppressor grid wired internally to the cathode ( e . g.22. Each stage used a Class B amplifier arrangement of EF8s, special low noise, " aligned-grid " pentodes . 23. When a tetrode or pentode is used, the screen grid voltage is usually about one-half the plate voltage. 24. A further bonus was that third harmonic distortion was much reduced relative to a comparable pentode ( Terman pp 198 9 ). 25. The beam tetrode design was also undertaken to avoid the patents which the giant Philips firm held on power pentodes in Europe. 26. After World War II, pentodes were widely used in TV receivers, particularly the successor to the EF50, the EF80. 27. Pentodes of the same power dissipation are capable of higher output power than triodes, but distortion is higher and more objectionable.28. The vacuum tube is then known as a triode, tetrode, pentode , etc ., depending on the number of grids. 29. Pentode tubes used in this circuit have a negative transconductance of only around-250 microsiemens, giving a negative resistance of-4000?.30. Later tetrodes and pentodes such as 817 and ( direct heated ) 813 were also used in large numbers in ( especially military ) radio transmitters
