You can install an effects loop in pretty much any amp.
I have done it with a Fender Bassman. The board was originally intended for Marshall heads like a Plexi.
But it takes bravery, and skill.
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Your ability to tweak the levels by changing resistors, etc is a big plus.
Let's face it, the design is only "ball-park," it's not perfectly matched to all pedals and all signal levels. But with some fine tuning you can get it dialed in pretty good.
I also added a series / parallel mix control which allows using the loop either way or bypassing.
I would have used a much better adjust pot than the one that comes stock...
I would have used Cliff UK jacks instead of the knock-off China jacks that come stock on the board.
But there ya go - project fun. I had fun with it and it sounded pretty sweet once I did all the tweaking to dial the levels in just right.
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