If using old stock EL84’s as opposed to EL84X – some may have pins that are open circuit (not connected) on modern EL84 and parallel types and officially marked “NC” (no connection) internally connected (Mullard specifically).
It is debatable if modern types that comply with “no connection” or original types (which in effect do not follow issued specifications) are “correct”.
The Retro allows either kind of valve to be used but if NOS EL84 are used the 4 jumpers should be removed and if using EL84X supplied by iFi the jumpers must be fitted.
Remove the jumper for any EL84 Type tubes that are not supplied by iFi. Bias is automatic and will work for all EL84 equivalents.
With the jumper removed pin 1, 6 & 8 are open circuit in the amplifier, to conform with the Philips EL84 specification which lists all three of these pin’s as “i.c.” (internal connection).
