It is important info for those of you who want to use NOS EL84’s ( 6BQ5) in modern amps and even not so moderns amps.
There are several modern EL84 amplifiers which have wiring violations on pin 1 of one or more EL84 sockets. NOS EL84s have internal connections between pins 1 and 2 where modern EL84s do not. Sometimes designers of EL84 amps assume that pin one is a safe location for a “tie point”, a place to connect a grid resistor and the signal wire from the phase inverter. This will result in a NOS tube placed in such a socket furiously “red plating” and the amp humming. If ran this way for long enough, damage to the EL84 tube and/or the component connected to this socket will result.
These amps can be modified by disconnecting and moving this junction off of pin 1. Best options and methods will vary from amp to amp with non PC mounted sockets being the easiest to modify. Contact a qualified amp repair technician to do the work. Read more ..
Reproduced by kind permission of Mike Kropotkin . You can check out his site
He is based in the Sterling Virginia, USA and specialises in NOS valves /tubes, re-issue valves and does amp repairs/mods.