I am restoring two Panasonic walkmans (RQ-S75 and RQ-SX33). I am wondering if it makes any sense to replace the large plastic pulley on the opposite side from the motor with a brass one that I have out of a part unit (RQ-S35V). They look to be the same size. Not sure if it would be beneficial, do nothing, or even possibly detrimental. What are your thoughts?
The pulley that drives the geartrain on AR90 mechanisms existed both in brass and plastic versions depending on model and generation. In my opinion, Panasonic decided to do this change because they obtained similar performance at a slightly lower cost. Then that pulley isn't the flywheel, so it won't influence W&F in a direct way. Rather, if that pulley has a sufficient mass its own inertia can decouple some of the geartrain non-uniformities. In reality though that pulley is very light even in brass form compared to the resistance during play when clutch is slipping. Also, in this type of mechanism the geartrain is decoupled from the flywheels through the belt itself, this alone rendering better results than a mech on which geartrain is driven by one of the flywheels. Where the mass does matter more is on the flywheels, although not a huge factor since these walkman flywheels are still very light even if made of brass (1/10 of deck flywheel weight). Guess there's only one way to find out the question to your answer: change that pulley without changing anything else and do W&F measurements before/after.
Thank you Valentin for the excellent reply. It is an experiment I hope to do after dealing with other issues I am running into with the players.
Hi! This is my first post here lurking for many years but couldn't stay outside anymore @AlexG your question regarding the brass or plastic pulley variants in the AR90/AR90iv mechanics is a valid one imho. Based on the experience I have with the RQ-S15(x2)/25/90R I noticed that the brass pulley in the S15(AR90) and S90R(AR90iv) makes is easier to get lower w&f (RMS 0.18/0.12%) compared to the slightly newer S25(AR90iv) (RMS 0.5/0.3%) with the plastic pulley. This is merely an observation after having all of them restored as good as possible. The S25 was a disappointment which I believe could be caused by the plastic pulley - hopefully. Going to replace it with a brass one in the future. (From one of the S15's). @Valentin Based on your thorough response I guess there could always something else at fault here causing the increased w&f and that being minimized by the slightly heavier pulley. /Per
In order to know for sure if it's indeed the brass pulley that lowers the W&F, you must test the same unit with both brass and plastic. Otherwise yes, there can always be other factors like the wear on capstan bearings, which has a huge impact on W&F. Had situations when an AR90 (brass pulley) couldn't obtain W&F lower than 0.4-0.5% WRMS, but after the mechanism chassis was replaced with one with lower wear on the bushings (all other parts remained the same) the figure dropped to 0.16% WRMS. Correlation does not mean causation, fact you obtained better W&F on the units with brass pulley doesn't necessarily mean it's the pulley that's casuing the low W&F. Only way to eliminate other factors is test the same unit with different pulleys. I would start with the one obtaining 0.12% and install a plastic pulley in it. If the assumption is correct, W&F should increase ~2.5 times by replacing just the pulley. Everything else must remain the same, including the belt. It would also be interesting to weigh these pulleys to see how much heavier the brass is.
Yes, good points there and my reasoning was a bit simplified - apologize for that and also, I forgot to mention that for both the S15 (with good w&f) and the S25 I used a slightly thicker belt (0.7mm) as an experiment and it could be that the combination of a thicker belt and a lighter plastic pulley is simply not a good one. I'm going to perform some more tests with the S25 hopefully this weekend. Thanks, Per
