Need Bias Help VC50H by SLM Crate

[hewo]

what's negative bias value for this class AB quartet EL84?
quartet redplates so either there is misfit of dc negative supply and/or dc negative value inappropriate for matched quartet "hardness" versus "softness" rating.
should improvement be performed by installing "tunable" negative dc bias voltage? scope can visual the sweet spot for tuning bias.
thanks in advance

[Jazz P Bass]

Is the bias voltage stable (Vac ripple, measure it)
The idle bias voltage , ball park, -14 Vdc.
Which depends on the tubes.
Are the EL84 tubes new?

[hewo]

bias vc50h

Is the bias voltage stable (Vac ripple, measure it)
The idle bias voltage , ball park, -14 Vdc.
Which depends on the tubes.
Are the EL84 tubes new?

schematic 15.7 negative dc volts but internet says footswitch is reason for cutout going in and out, not bias derived.
so must now check normally closed contact fingers of footswitch port receptacle

[hewo]

tubes ok but need to augment pcb with bias adjust (potentiometer). can u pl direct this?