Hoffman has a ckt. schematic for "adding reverb to the Western Electric circuit" posted at his web site. It requires an extra 12AX7 and uses half of the 12AY7 as a gain stage pior to driving the reverb tank (tank is driven with half of the extra 12AX7) second half of added 12AX7 is the recovery amp. I built this into a tweed Bassman ckt but did not like it. Not enough reverb. I added an auxillary 6.3 heater xformer and used two additional tubes, one 12AT7 to drive the tank, one 12AX7 as an O'Conner style "tweed mixer". I split the signal after the 1st gain stage - .02 cap to 'tweed mixer', then 500pf cap (like the std. Fender BF reverb) to the 12AT7 reverb driver, the second half of the 12AY7 (who needs two inputs??)is used as the recovery stage then goes to the other side of the 'tweed mixer'. The mixer feeds the original 2nd and 3rd gain stage 12AX7 via a 1meg pot. Sounds great to me and go from just atouch of 'verb to Grand Canyon echo!