Interesting socket has been added as a slave out from the speaker outputShame it is a PCB rather than Tag strip hand wired oneThis is the Vib Trem area will check all component valuesIt uses 3 valves for the Vib Trem function!Nice Chassis but no Valve rectifier this is solid state on this ampIt turned out the 12AU7 was in the wrong slotElectrolytic in the centre was the issue , open circuit causing the oscillator to no oscillate!Showing the old cap and the new one I replaced it with VOX AC30 in to get its Vib Trem working! This one is from 1977 and has a PCB and Solid State Rectifier.. it is well used but sounds good, recently had new valves but the Trem function is not working.