This has me wondering if it's not the output of the Audio amp - what about the input side?
Thinking the Bootstrap or the input AF Amp that takes the Volume control output and that has a cap C224 a simple 1uF 50V cap. You're thinking age so lets look at this from a standpoint of - If I was this radio and I was built when Ronald Regan was still in office - He's' gone - I'm not - so why do I still hear echoes?
I'm referring to the typical "Thunk" heard from a power on this thing does.
I mean a side to side comparison is probably out of the question but if "low volume" - is there something further up causing this?
It mean spend some quality time with it - put it by the fireplace and offer some marshmallows - talk to it nicely and then threaten to use a very hot poker to resolder some of those cold solder joints it's been creaking and groaning about as of late...
(The above is Done In Jest - do not attempt to do this type of repair at home or with a hot poker)
I'm referring to the quality of audio not quantity - there may be a failed cap - but like at C46 the AF Mixer deconversion (Q16) or questionable Q17 SQ amp - kinda acting like it wants to but - nah - too old to start acting like I'm a kid again - sort of operation - marginal cap (read highly resistive ESR rating) Thats C49 the output line from the IC1 Quad Op amp - so a recap may not be in order but this sounds like it wants to be...
The Things got a PA - so use that same speaker and try it on the PA MODE to see if you GET A REALLY REALLY LOUD SQUEAL from it...if you do - then recheck the Volume control and its' support parts - like that cap.
You can then rule out the Audio Amp - the problem is further upstream
