Old Transistors.

I am not famialer with that model, but I have had a fair amount of broken consumer electronics cross my bench over the years so what follows is general and may not be useful in this case.

I am in a similar state if you need data, though it can sometimes take a bit of finding - I literally  have tens of feet of shelves holding data books for transistors and ICs from various eras on the wall in my dining room (and more rare access stuff in the loft.... )

But unless they have been overheated by being soldered on short leads, the old germanium devices are remarkably reliable in themselves,  partly as the internal dimensions on chip are very large and the fabrication methods quite agricultural by modern, (near quantum mechanical limits) standards. (The youthful naked eye could actually see the metalization patterns on 1960s  devices, now I need glasses)  For the related  reasons ESD is less likely to damage the older devices, party as they are bigger, and partly as they are electrically leakier so charge is less prone to build up.

Quite commonly if an old transistor fails, in a design that was previously reliable, there is another defective component in the process that has stressed it, such as a PSU fault or a leaking electrolytic capacitor increasing the bias current to the base, or a bias resistor that has gone open circuit, again changing the operating conditions. So if you just change the transistor, take care that the voltages are in-spec around the replacement, or you may end up changing it again shortly.

Germanium has a much lower temperature chemistry, so is less tolerant of heating -  by 100C the devices are well on the way out, so when soldering be very quick, and if need be use wet cotton wool buds or a pair of pliers as a heat shunt. Easiest is to leave the leads quite long.

The intermittent knock and work problem is unlikely to be semiconductor, or if it is, it will be associated with a mis-soldered leg. I'd be looking for a hairline PCB crack or a solder joint that reveals the fault when prodded with a dental pick or other sharp point. I assume all switch contacts and potentiometer sliders have be given the electrolube treatment ?

I am not famialer with that model, but I have had a fair amount of broken consumer electronics cross my bench over the years so what follows is general and may not be useful in this case.

I am in a similar state if you need data, though it can sometimes take a bit of finding - I literally  have tens of feet of shelves holding data books for transistors and ICs from various eras on the wall in my dining room (and more rare access stuff in the loft.... )

But unless they have been overheated by being soldered on short leads, the old germanium devices are remarkably reliable in themselves,  partly as the internal dimensions on chip are very large and the fabrication methods quite agricultural by modern, (near quantum mechanical limits) standards. (The youthful naked eye could actually see the metalization patterns on 1960s  devices, now I need glasses)  For the related  reasons ESD is less likely to damage the older devices, party as they are bigger, and partly as they are electrically leakier so charge is less prone to build up.

Quite commonly if an old transistor fails, in a design that was previously reliable, there is another defective component in the process that has stressed it, such as a PSU fault or a leaking electrolytic capacitor increasing the bias current to the base, or a bias resistor that has gone open circuit, again changing the operating conditions. So if you just change the transistor, take care that the voltages are in-spec around the replacement, or you may end up changing it again shortly.

Germanium has a much lower temperature chemistry, so is less tolerant of heating -  by 100C the devices are well on the way out, so when soldering be very quick, and if need be use wet cotton wool buds or a pair of pliers as a heat shunt. Easiest is to leave the leads quite long.

The intermittent knock and work problem is unlikely to be semiconductor, or if it is, it will be associated with a mis-soldered leg. I'd be looking for a hairline PCB crack or a solder joint that reveals the fault when prodded with a dental pick or other sharp point. I assume all switch contacts and potentiometer sliders have be given the electrolube treatment ?