AB763 Query - Run Normal Channel Directly Into 3rd Gain Stage? (not to reverb)

[tdvt]

Regarding my UL Pro Reverb rehab project, I have been researching all the "Normal Channel" mods that have been posted over the years & I am currently leaning toward simply rewiring for trem/reverb on both channels as I can see that making the normal channel useful.

But looking at the schematics, I am wondering about feeding the signal from the two V1 stages (Normal) into the grid of V4B (reverb recovery/3rd gain stage tube), right after the 3.3M/10pF combo, with the intention of an added gain stage on the Normal Channel without reverb circuit losses.

With some additional TS tweaks, it could be a non-reverb lead channel.

OR, is the reverb circuit signal loss already made up by the time it gets to that point in the signal path, making that idea not worth the trouble?

[tdvt]

So after trying the reverb/trem to both channels mod & not really finding it that useful, I decided to see how running the "Normal" channel into the last "Vibrato" gain stage would work.


I guess the core of my question in the previous post was how different are the strength of the outputs of the two channels, to be able to successfully sum them at the grid of V4b (last triode before the PI)

I wanted to keep the Vibrato channel as stock as possible, as most people default to that channel & have the modded Normal channel enhance the overall versatility. 

So, I tried a few configurations & this (drawing below) is what is currently tacked in place and is headed in the right direction.

The post-V1b 1M pot was initially a variable resistor for level matching, & was then connected in a volume control configuration. Even though the two level pots are on either side of the same tube stage, you can play one against the other for more or less drive.

I also moved the V4b grid leak to the downstream-side of an added coupling cap, which more or less replicates the channel mixing at the 3rd gain stage of an AB165 Bassman.

Reverb is still only on the Vibrato channel, but Trem is on both since that is implemented just downstream of the 3rd gain stage

Since the channels are now in phase, they can be jumpered & mixed to taste, but I need to build an ABY box to try external channel switching before deciding to wire this in for real.

[AlNewman]

Have you tried it yet?  Looks like in your drawing the 3.3M limits the reverb signal, only allowing high frequencies through to the tank.  In the original design, the 3.3M attenuated the main signal, reverting more signal to reverb, while allowing high frequencies through to the next stage.  At least that's how I figured it works.

[tdvt]

Have you tried it yet?  Looks like in your drawing the 3.3M limits the reverb signal, only allowing high frequencies through to the tank.  In the original design, the 3.3M attenuated the main signal, reverting more signal to reverb, while allowing high frequencies through to the next stage.  At least that's how I figured it works.

This is currently in place & I have been fooling with it as shown.

The section with the 3.3M is all stock, pretty sure it is drawn right...

Here's the real schematic with the reverb section ▼▼▼

[AlNewman]

Cool.  I think the vibrato channel has too much gain anyways.  And the reverb seems to wash out.  You're probably on to something.