my little Arvin 68R05 has distortion worse at higher volume but noticeable all volumes. studying output bias check. wish I had the print to make things easier. although I am guessing p/p NPN. resistor close to it. do not see thermistor

That schematic is in TSM-89.
I have the issue, but it's going to be a few days before I can get to scan it for you.

~ Mitch ~

thanks Mitch. just found a TSM-89 of my own. one of the guys is getting rid of his Sams. now I have a print will be checking bias and voltages where they should be

DC voltages look close enough. must be an AC component garbled somewhere. a different speaker with unit speaker cut-out from earphone jack still has some distortion more noticeable at higher volume. maybe a ceramic signal capacitor breaking down. could re-check electrolytic installation

yep definitely an AC component. not that I checked it with a scope or anything.
some history this was the first pocket transistor AM receiver that I had worked on. having nearly zero volume first off I replaced electrolytics with what I had improving volume considerably. sounded pretty good. the 50uF axial lead battery bypass that I crammed in there had never been used before. must have been far from new or at least poor quality. recently buying 47uF radial from Mouser I suspected my original replacement. wow what a difference. no more gargle grunge audio. cleaned it right-up. distortion gone. I changed another that should have been 10uF but had a 33uF in there from volume wiper to audio driver. although it is now 10uF like it should be I didnt notice any big difference maybe because I changed it before the 50uF. but is working great now. thanks to all and to all who like a good story

ever heard of Iskra brand electrolytic capacitors ? they suc so far
found this about battery bypass

"Without this, signals induced on the battery voltage by the high current taken by the output stage will feed back along the power rail into the earlier stages. The result is a low frequency oscillation at high volume settings."

yep

Glad you got it sounding good !

Never heard of Iskra caps...

Any pics ?

John

dont know where I got these Iskra electrolytic. probably at a swap meet bargain bin. these are medium silver blue color axial lead 47uF electrolytic. kind of a bevel nozzle on the + end. no photos no camera sorry

I love a happy ending !
Nice to see it working again.

Made the mistake of buying 'new' electrolytics at a
swap meet and found out later that they're NFG.
(No Efffing Good). - Never again.

Was digging through my Sam's Photofacts and
found a nearly identical Arvin in TSM-21.
I'll try to dig it up again when I get back.
The resemblance between yours and the old design is uncanny.

~ Mitch ~

I believe that some paint chips fell inside the tuner after adjusting the trimmers on the back of the plastic encasing. the adjustment screws held in place with color paint that chipped-off while turning screws. there is some crackling while tuning at certain spots on the dial. vacuum cleaner didnt help much. teeny-tiny nuts hold things together on the back tuning cover. might have to remove the cover to clean things up a bit