Effects Loop Questions

[Rontone]

I'm fitting an FX Loop into an amp, following the Valve wizard site and book, I've added schematics below, one is an example patched in to a JCM800 type amp, this amp I have is practically the same driver into EL34 power, but the two channels are coming in from 220k mixing resistors

- First I was thinking of powering it from the power supply node that the driver is on, it has a dropper resistor from the HT [Rp in the schematic] what would be a good voltage for the tube to be on?

- If I do tag-strip nearby to link the tube to the jacks and pot, should all the grounds go back to the preamp grounding bus bar, or can I do local star grounding, on the tagboard stand-posts for example, same goes for the cathodes on the FX Loop tube can they just be locally grounded to the chassis?

- The input cap C1, I already have coupling caps on my channel outputs, then 220k resistors where they join to the driver, so I don't think I need that C1, or do I?  Also C7 output coupling cap, should that be roughly similar to previous stages, 0.022u - 0.047u?

-C2 are both cathode bypass caps, in the cathode follower cap, does it still have the same effect on bass and freq. response, can I fiddle with it? Also in a cathode follower are those caps a similar voltage safety range, or should they be raised?

- C5 small 100pf cap, as with grounding, can this be just on the socket, soldered directly from grid pin to chassis or tag ground?

[PRR]

Where did you get fxlooppcb2.jpg ? Surely not from Merlin?

[HotBluePlates]

Where did you get fxlooppcb2.jpg ? Surely not from Merlin?

https://www.valvewizard.co.uk/fxlooppcb.html

[Rontone]

Where did you get fxlooppcb2.jpg ? Surely not from Merlin?

Yeah, its on the site, so I was hoping that was OK to pinch, as I have seen others posting his pictures from the site,

I didn't have to pull a soldering iron out of a stone to get them

[RadioComm]

Hope this helps... Build and installed an effects loop into my JCM800. Works great. Here is the link:

https://el34world.com/Forum/index.php?topic=28311.msg311807#msg311807

Good luck

[Rontone]

I got a bit more done on this and fitted some hardware to start wiring it up,

I need help with the input and output of the FX loop, should it have attenuators as done in the pictures, I'm just wondering what values to try?

I have annotated a picture below of the rear panel with the master volume control, I can take the output from the tube and couple it with a cap to the tag board, then a resistor to the next tag, then split to the master volume pot,

On the main board there are some spare turrets, I have a space to add a coupling cap from the channel mix resistors then any attenuator resistors there too

[Rontone]

I could do something like this