SFPR reverb tap

Hey there, all. I've got this idea to tap the output of the reverb circuit of my silverface Princeton, and I could use a little guidance from people with more tube circuit experience than I. The idea would be to be able to use it as a mixing send (with a reamp on the input), so I'd want to tap just the verb output, and none of the dry sound. At the same time I'd be rewiring the ground switch as a standby, using it to short the control grids of the power tubes, thereby killing the speaker OP while leaving the B+ voltage unmolested.

I was thinking the best location for the tap would be directly before the reverb level pot, right after the recovery gain stage's coupling cap. However I'm not sure about a couple of things:

1. What are my level/impedance etc. considerations? I guess the recovery stage has a certain range of OP impedances it would like to run, and I'd want to stay in there. How do I achieve this? Do I need to pad the output (maybe with a 470K resistor, as in the stock OP path)?

2. It would be great if I could output at line level, maybe via some sort of opamp buffer, or even a trafo if I want to shell out. I'm thinking this may be more hassle than it's worth though, and I'm expecting I'll probably OP at more or less instrument level and use a DI to get it back into the mix. On a related note..

3. Can I just have the tap run parallel to the normal output path, or do I need to put in a switch to keep the tubes happy (maybe using a switching jack or something)?

Thanks in advance for your input, folks.

12AX7's are very picky about the load they work into, and are already gain reduced by the 100k load of the mix pot, add a parallel circuit and you will lose even more gain. You will need to buffer or switch

I don't think that a single 12AX7 is going to give you enough gain to get to line level unless the reverb driver is healthy, so I expect you will need some additional gain after it to output line level.

No on the parallel without some buffering. The switching jack is a cool idea, but won't work if you have additional gain in the "out" signal path.

If you don't want to use a manual switch, and I can see why you would not, then I would suggest a follower as a buffer between the tube and the mix pot that can feed both circuits. Were it me, I would use a LDN150 depletion mode N-channel MOSFET. You will not come close to clipping it, so it will be more transparent then a tube follower and does not require a socket or heater current. Treat it like a 12AX7 as far as circuit values go and it will drive both the mix pot and the OUT socket if the load is reasonable. It will raise the impedance of the load the recover 12AX7 is working into so you will get some extra gain from it. If that is still not enough gain then there are a few ways to go. Easiest to explain would be another LND150 wired as a gain stage, it to will be transparent if you don't clip it.

yeah, that's about what I figured re the parallel lines, and also the gain. Right now I'm thinking I'll probably just use a switching jack and plan on running it with a DI box and a mic pre. I'm assuming the level coming out of the recovery amp is probably hotter than standard level, and I'll probably have to pad it some, yes? I'd do the gain calculations myself, but I'm still not too facile with the numbers on tube stages.