The data sheets on this page come from the third volume of a three volume valve (tube) and semi-conductor manual issued by Amperex in 1965. Other valves encompassed are the EL34, EL84, ECC82 and ECC83. Some of the sheets originally came from Philips, others from Mullard. Those for the GZ34 are dated 1958.

The valves used in guitar amps generally come under the heading of "Special Purpose Tubes" in manuals published in the USA in the 1960s.

The GZ34 was used in all JMI-made AC30s from 1959: the single speaker AC/30; the AC30/4; and all types of AC30 Twin.

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