This circuit went on to define 70's rock and created the sonic landscape most people/players associate with Park/Marshall™ Amps. The P50M amp circuit defined a whole generation of music and was the bridge between the Park 45 and the Park PMV (Cascading channels and a Master Volume).
The Park P50M is the first split cathode amp by Jim Marshall allowing channel one to be significantly brighter and cut through the mix - a small change to a classic design with really big results. Increased filtering added a more immediate player response and a stiffer feeling from the power section.
Mitch Colby’s signature mods (now standard):
- Push-pull pot 1 - upper mid boost across both channels
- Push-pull pot 2 - applies separate value bright caps across both channels
- PPIMV.- Post Phase Inverter Master Volume now standard - overdrive the Park P50 at lower volume levels - or crank the Master Volume to effectively remove from the circuit as in the original Jim Marshall Park P50 design.
The PPIMV is a volume control after the signal is split by the phase inverter tube and just before it goes into the power section (tubes) of the amp. Because the PPIMV comes after the phase inverter tube it benefits from a little more added ‘overdrive’ when compared to the PrePIMV.
A neat trick with the PPIMV is that by cranking it you are essentially ‘taking it out of the circuit completely’ and hearing the amp without a Master Volume which only became available in later models.
- EL34 tubes = classic British tone
- 2 Channel / 4 Input (`Jump` the two channels for additional tonal range and tube saturation).
- 40 Watts clean, 70 Watts cranked.
- Solid state rectifier.
Wattage: 50W
Channels: 2
Inputs: Channel 1 High, Channel 1 Low, Channel 2 High, Channel 2 Low
Output: 2 x 1/4" Speaker Out
Impedance: Switchable using Impedance Selector on the rear panel — 4 Ω, 8 Ω, or 16 Ω
Preamp Valves: 3 x 12AX
Output Valves: 2 x EL34
Controls:
Channel 1 Volume, Channel 2 Volume
3-Band EQ shared by both channels — Bass, Treble, Middle
Brightness (Presence) shared by both channels