Finishing Up Plexi Build

I finished soldering all of the components and will begin checking all connections prior to the initial power-up.

I have ordered 3 12AX7s and 2 EL34s for testing of the amp next week.

Chassis Wiring

Front panel without knobs.

Rear panel without knob for NFB.

Top view of chassis.

Edit 10/31/19. I successfully powered up the amp with all tubes installed.

V1: Ruby 12AX7AC5 HG+
V2: Shuguang 12AX7
V3: Sovtek 12AX7LPS
V4, V5: Electro Harmonix EL34 matched pair, average distortion

B+ voltage off the HT fuse is nominally 432V, in line with typical '68 Plexi 50W voltages.

Below are some additional photos of the completed amp.

Front view with cage and knobs installed. I will redo the Midde and Treble Dymo labels.

Output section wiring.

Power wiring.

Input section wiring.

Switchable mod wiring.

Tone control wiring.

Initial observations playing through IRs loaded by Suhr Reactive Load:

• The bright caps increase the noise floor of the amp, especially when the channel has a bright mixer capacitor engaged. Adding gain through the V2A cathode bypass cap does not result in as much noise.
• Engaging a bright cap with the bright mix capacitor off on the active channel does not increase the noise floor as much.
• I have 2 near-identical channels in shared cathode mode, by engaging the bright mixer cap for the active channel, and turning it off the the unused channel. I can set up four different bright cap values this way.
• The 4700pF bright cap (channel 2) immediately distorts the sound as expected.
• 500pF on a clean sound is too bright, even on shared cathode mode.
• The lead channel in split cathode mode is noisy when I turn it up to 10. This is more gain than I need, and I am ok with the noise floor when I dial the amp back to 8 (Fender-scale).