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.
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| Chassis Wiring |
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| Front panel without knobs. |
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| Rear panel without knob for NFB. |
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| 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.
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| Front view with cage and knobs installed. I will redo the Midde and Treble Dymo labels. |
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| Output section wiring. |
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| Power wiring. |
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| Input section wiring. |
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| Switchable mod wiring. |
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| 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).
