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Old 26th August 2012
Gear Nut

Originally Posted by Studerfreak View Post
If you take the head cover plate off, you will notice a adjustable capacitor C61 (trimmer) which controls the amount of HF bias.
Here's an update about my machine: tape path is ok, relapped heads are set up, here is the frequency response (Rec 15ips):

Hi frequencies are still increasing more than they should but global sound is ok, even with this extra high end... I'm really intrigated by the fact I can't set up hi freqs, I mean Rec Eq pot is fully counterclockwise but still too much highs. I already encounter this on my J-37. That's why I'm wondering about SM900...

I've been unable to set up the Bias with hi freq, there are 2 successive peaks. So I went to your 30Hz method and everything was totally clear then, I choosed the second peak to overbias then :-)

After 250nWb alignment, I tried a 355nWb one (15ips). Seems to work!

Unfortunately, one issue's remaining, some bad 50Hz buzz and tons of harmonics: noise is @-41dBu at powering up, I mean without playing/recording on tape... Not happy with that as I don't know how to figure it out :-(