Modern EL84 amps and NOS EL84s
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 run 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.
Known amps with this problem:
Dr Z Maz 8: Serial numbers before before SN: Y32229 OK (Y stands for the year 2014, X 2013, Z 2015, AA 2016, etc.) SN: Y32229- Y32253 all had the pin 1 connection from the factory. Some of these may have been reworked at the factory. Anything after SN: Y32253 is OK (eg Y32254 and higher).
Lexicon Signature 284
Laney VC30, Laney L20H (Probaby safe to assume all Laneys are off limits)
Fryette Memphis 30-Only applies to outer 2 tubes on units with serial numbers (last 4 digits) 0141 or lower.
Jackson Ampworks Britain 3.0 and earlier (4.0 is ok)
At least one Mesa amp (but definitely not all), which I can't recall,has this situation.
Bad Cat: Hi, just thought I'd let you know that some new model Bad Cat amps tie the
EL84 grid resistors and PI leads to pin 1. I have a 2016 Bad Cat Black Cat 15R (newer model with
K-master) which built with the 1.5K grid stopper resistor across pin 1 and 2 with the PI lead also to pin 1.
I plan to lift that connection so I can use my NOS GE EL84 and some 7189 and 7189A tubes.
BTW, this amp doesn't have a connection to pin 6 (allowing 7189A).
No known problems with:
Bad Cat (some, see not above and contact Bad Cat or check your amp's internals) , Matchless, Dr Z (except for the Maz 8), Fender Blues and Pro Jr, Vox, Gibson Goldtone GA15s, Mesa Lonestars, Kingsley Amps, Jackson Ampworks Britain 4.0 (check with Jackson on his other amps), Seymour Duncan 84-50 and many other amps will work fine with NOS EL84s.
New models are constantly being added as well as changes to older models. ALWAYS contact your amp builder (or check yourself, if capable) before installing NOS EL84s.
Message from Laney Amps Technical Service
Thanks for the enquiry,
Older Laney amps before 2008 had hand wired valve bases and the resistors connected to the bases where anchored on the spare pins as mentioned below.
All newer amps with pcb mounted vale bases do not use the pins so you are quite safe to use NOS tubes on this amp.
Senior Service Engineer/Production Supervisor