schematic of the mods

 



Peavey Heritage VTX modifications

The schematic shows the new circuitry, plus just the relevant bits from the original VTX schematic, showing where the new circuit is tapped in.  I posted a link to the full VTX schematic, in an earlier page.

* add two new 12AX7 preamp tubes, housed in new chassis located underneath existing chassis.

* disconnect existing VTX solid state drivers from 6L6 cathodes.

* connect all four 6L6 cathodes to gnd.

* disconnect VTX dc voltage circuit from 6L6 grid inputs, preserving input resistors.

* cut existing connection between positive and negative phase inputs (6L6 pairs).

* connect phase inputs to new V6 12AX7 phase inverter circuit outputs.

* connect power transformer HV center tap (low-power setting) to new phase inverter bias circuit.

* connect feedback line from the 4 Ohm output transformer tap, to new presence and depth (resonance) controls associated with V6 circuit.

* connect +525v HV source to R-C power supply ladder for the two new 12AX7s.

* cut existing VTX preamp output line, just ahead of pre-out jack, and insert 3-way DPDT preamp selector switch (VTX, both, AB763+).

* cut line to existing VTX solid state power amp driver input, just after pwr-in jack; connect pwr-in jack to new master volume control, and then to the V6 circuit. 

* install new V5 12AX7 "AB763+" preamp circuit, along with associated controls, on new panel below existing VTX panel.

* (not shown in schematic) add control switches to VTX preamp (on new panel), duplicating footswitch functions: channel select (clean, both, lead), reverb (rvb), and phaser (phs).


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