First of all, thanks rootz, that you can build sims is brilliant. I'm going to have to get to grips with LTSpice at some point. There's a lot of guesswork over here at the moment but I had my doubts about just removing the filters and letting the current through. Before I saw your simulation over at https://ampgarage.com/forum/viewtopic.p ... 73#p410873 I was considering breaking the filter part of the circuit down into a lite version but preserving the impedance. I didn't really want to include a SSS filter and then I saw your version.rootz wrote: ↑Sun Apr 04, 2021 6:25 pm This looks very different from what I did when I crossed the 005 and 124 (or at least did an attempt). Can you explain why you'd want reverb on only the clean channel? You use an extra relay for the reverb, when you could easily use an extra relay to switch reverb level pots. With a DPDT relay you could actually switch reverb send and return controls. The Coral does that IIRC.
One thing that occurs to me as an error in your latest reverb schematic: how much signal will the reverb mixing triode see? There essentially is a 1:1 voltage divider on the grid of that tube, so it will see half the maximum output of the clean preamp! I think this means it will be very easy to overdrive the grid of the mixer stage. You need to dump more signal, like a filter section would.
It's been a while since I've been tinkering with different reverb ideas. Last time, I had a good look at many pictures of the Steel String Sultan from AN, which I was told is a clone of the HPD, which in turn is a clone of the 005. IIRC the attached picture is a schematic of the best I could make of all the pictures, including the lack of bypass caps for the mixer, rather strange cathode values for the 2nd clean triode, unbypassed ververs driver cathode resistor. Just ran some quick sims of it: 100mV input signal of 1kHz with all controls on noon gets me a whopping 42V peak-peak at the anode of the second clean triode. You do not want that on the grid of the reverb mixer; it would make your amp useless. After the filter I get 300 mV peak-peak on the grid of the reverb mixer triode, which translates to 8V peak-peak at the output. More than enough to drive the PI pretty hard with the master on 10.
So to summarise: dump much more signal before the reverb mixer triode, just like the filter would do.
You didn't really go into it at the time, the topic was about the #005 after all, but this is a version I cobbled together from your design. I may have got the path from the OD relay wrong, so I am trying it your way. I've also reconfigured the RVB relay to switch the level pots. I was unsure where to place it in the circuit, the aim being to isolate the RVB entirely but if I have this straight, this (with the level pots) does the same job.
) as low as 220k and the BF reverb is generally looked down on, as not the best way to do it in a Dumble. That sent me looking at #002, #013 and #060 but I returned to #005 because of the mixing triode and the two tube design. Space being a consideration. I do like the way you did it, so I'll take another look at your third option. I have faith in your design though and until I get a more complete understanding of how these circuits can be shaped, I will stick with it. Please tell me though, it appears you ran a couple of simulations of your 124/005 hybrid. In the simulation at the top of your screenshot R55 is a 6Meg8 resistor and in the one below, its equivalent is R238 5Meg6, similarly in the top simulation the cap and the resistor to ground are 15p and 68k, while in the one below, they are 22p and 82k. There also appears to be a 1 ohm resistor (R243) right before the mixer's grid in the top simulation. I'm not familiar with LTSpice so I can't know where the traces (alongside) are pulled from. Speaking pragmatically, I will simply be happy if it works, but I won't be content until I fully understand what's going on. My gut tells me that the top simulation would be less likely to overdrive the mixing triode than the one underneath. If so, that's what I would go for because I would like to keep the high end tame and let the 124 part of the circuit breath. Working systematically through the toffee-shop of mods that are possible it became clear to me that anything I added had to have as little impact on the 124 signature sound as possible. I expect the reverb will produce some hiss, I expect its impedance with will affect the tone upstream and down, but I want to keep that to a minimum. If it's to be any good, it shouldn't sound like a cheap pedal 
An extra gain stage (Reverb Mixer) 