Just to let you know I did the mods on the AU-555A and been listening the amp since!
I used 0.39uF Panasonic polypropylene type for the vbe by-pass and 1N4005 diode type (higher voltage rating) for the Baxandall mod instead. Guess these will do the job as well, since these were leftovers from previous projects.
In addition replaced the original transistors on the tone control board with HFE matched KSC1845 transistors.
The original bias trimmers were replaced by Bourns 3362P -type and adjusted bias circa 9.5mv after warm-up.
The 20k Bourns trimmers were out of stock at the local dealer, so must replace the center voltage trimmers later on.
The original bias trimmers at this point are really flaky. After removing them from the amp board, even if they came out easily, I really can't get a sensible reading out of them. So it's highly recommended to replace them as well.
Tested the original 2SC871 for HFE readings.
I got 600, 548, 534 and 651 from them.
The fresh KSC1845 Fairchilds measure for 429.
I can't really comment on how much the mods improved the amp, since I figure the amp is still burn in -process with Silmics. There must be some truth to the reports that claim silmics burn in take way longer than with regular caps. However I think the noise floor have reduced a bit, transformer hum is still present, but it's not so persistent anymore as I recall it from the first listening perioid.
