Had 10dB higher gain preamp. Full audio pro rev 6 modification. Has T.H.E. tube harmonic equalizer circuit. Updated mic pre with RFI suppression. Updated tube plate volts. Updated low frequency EQ predominance. Phase corrected filter. (No loss of extreme deep bass) Has complete mod of tube vactrol auto compression and EQ at 0 dB. SN 4930. Has box. Condition #9
