Help with a Tube EQ circuit

[evengravy]

Hi,

I have been given a circuit diagram of a tube based EQ unit and I need some help if anyone could help me I'd be gratefull.

Basically the circuit is in two parts a Tube base amplification stage and a "passive" inductor based EQ circuit that "appears to me" to be in the feedback path of the Tube amplification stage allowing for both boost's and cuts to be applied at the set frequency ranges.

The EQ section is fairly well understood and I have worked out the multi tapped inductor values based on the given frequencies and capacitor values.

I am having some issue understanding the Tube topology however, I am not at all experienced with Tube designs. My initial analysis from staring at the circuit for some time now is that the tube amp circuit is essentially forming an op amp.

What I would like to do is replicate the EQ unit but replacing the Tube amp stage with a solid state amplification stage keeping the EQ pretty much as is.

Could anyone help me understand how to do so? could I possibly use standard opamps in some configuration? or could someone help me "decode" the circuit so that it could be replaced with BJT's of JFet stages?

Sorry for the long post, thanks in advanced, even