I recently built a Super Reverb’s “reverb” channel into a Princeton chassis and cab. I encountered blocking distortion at high volumes — it happens in some builds. Seeing as how most amp “info” on the internet is usually “old wives tales” of sorts (people just continually passing on hearsay), I figured I’d start a thread here to ask for electrical explanations and solutions, rather than repetitions of hearsay found on an old website. Blackface amps seem particularly susceptible to blocking distortion. I’m hoping this thread can be of service to others experiencing this issue in new amp builds or vintage buys. — 1. GRID STOPPERS: My 6L6s grid stoppers are 1.5k. The amp is built to the AB763 schematic (with the Normal channel and its tube omitted). Is there an ideal size for these resistors? Everyone seems to guess blindly in the dark as to values that eliminate blocking distortion while not dragging tone and treble down. I don’t want to leave tone up to guesswork. 2. PHASE INVERTER INPUT CAPACITOR: Phase Inverter input cap is 0.001uF. Is there an ideal PI input cap size? We can do better than blindly guessing on values here. Some bf Bassman had a 500pF PI input cap. Is there a better way to calculate the ideal cap size here (given that we already know the guitar’s lowest frequency)? 3. REVERB DRIVER TUBE: The reverb driver tube is brand new (JJ tube)... but given how hard these tubes are driven (generally around 400 volts for a 12AT7), blocking distortion is often derived from this part of the circuit. Are there any improvements to this circuit to eliminate it as a source of the problem? — These are the usual three suspects, but feel free to help us all out if you have more tips/tricks (I already used shielded wire on the inputs).