Dating vintage celestion speakers
There was no HT (High Tension) to the driver valves, there was a short under the large resistors that drop the voltage for the different HT sections.Several faults on this one, there was 3 V on the o\p of the right channel which was caused by the 18V Zener in the power amp s\c.This was not working, not surprisingly, found the left channel had blown loads of resistors and transistors.
I had to replace the connectors with wire links on all 5 boards and wire link all the through links on the main circuit board, over 100 of them! There were several dry joints on the phono eq boards as well, sounded okay after all that. The 25 V was missing, there was a pre-set adjustment on the board which did nothing, a modification had bypassed it!I found the capacitors (the square black ones that gave problems in the AU-919) had lost their capacitance, mainly the 10p F ones.Vintage integrated amplifier from Sansui dating from around 1965.There are fusible resistors used in the power amp section and the preamp section that are going faulty, ie high resistance for no reason, they are 150 ohm in the power amp and 82ohm in the pre amp, the sound becomes distorted and weak when they are the wrong value.There are 2 sets of the 82ohm resistors, one is on the RH vertical board and the others are under the front cover behind the switches.
All three of the transistors in the regulator required changing then I noticed the power amps bias was wrong, all 4 and the o\p DC levels were around 400 m V.