Mullard five-twenty, 5-20, 520

A twenty watt valve audio amplifier 

The original line-up for this amplifier was 2xEL34, ECC83, EF86 and GZ34 rectifier.

Given that this is a far from compact amplifier - 2 large transformers and a large choke - there's no reason for not using octal valves throughout.  The octal equivalent of the EF86 is the EF37A (6J7G), and the octal equivalent of the ECC83 is the ECC35 (6SL7GT).

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