Tone pot dating
It has half the number of power tubes, smaller transformers and a tube rectifier in stead of diodes.Together this makes the Pro Reverb break up significantly around the usual volume level 4, while the Twin Reverb is clean almost all the way up.This mod does not change the amp’s clean headroom but increases the preamp gain and preamp distortion.This mod is one of Cesar Diaz’ tricks in the Fender Custom Shop Vibroverb 64 which he always did to Stevie’s amps. It has stood the test of time and been been done by players in 50 years in blackface Fender amps.This is the preamp tube for the normal channel which you are not using when playing the Vibrato channel.Vice versa; If you’re using the Normal channel, you can pull out the V2 tube.Five fundamental tricks to create the holy grail of Fender tone Here is a video demonstrating the effects of some of the mods and tricks described here.
Like all silverface amps, the Pro Reverb was modified in the CBS periods to increase the clean headroom making it thinner and harder sounding.Having an AB763-similar circuit, there are many mechanisms in the circuitry that you can tweak to suit your needs, basically to increase or decrease the clean headroom.Personally we like to mod the amp so we can make it smaller when needed.The reason is that 12AX7 tube has a voltage gain factor = 100, while 12AT7 = 60 and 12AY7 = 45.
Pull out the V1 normal channel preamp tube – More preamp gain in vibrato channel We’ll start with saying that this is a mod we personally do to all dual channel blackface, silverface and reissue amps.
The power transformer and power tube circuitry is equal to the Super Reverb, but a smaller output transformer lowers the clean headroom and introduces sag and breakup.