best reverb for tube amps series effects loop? tone suckers fear

[andyhumb]

I want to add a reverb unit - maybe some delay - to the series effects loop of my tube amp - anything I plug in changes my rhythm tone, makes it less tube like. I know that modern effects units need to do a A/D then D/A conversion to get the signal pack to the power amp section and that effects the tone, even with the effects unit itself in bypass mode (it still goes through the effects unit). Any really good reverb units that won't digitalize my sound. I've tired the Lexicon modern MPX-1 effects unit (like a good version of the G Major) and old Rockman gear - they all negatively effect the rhythm tone in my opinion. I'm toying with the idea of turning it into a parallel loop