RGR Model 4 Pre Amp ....HUM QUESTION

The RGR 4 was in 1980 a giant-killer preamp designed by Robert Grodinski of pro-audio RG Dynamics fame. Sonically as good as - or better! - than the then- current champ - the $4500 Levinson ML7. So for $650 one could buy a SS preamp in the same sonic class as the Levinson.

After reading your post I tried the RGR 4's tone button. Voila, pushed it in and hum GONE! 

I nailed it on the first post, lol. On a preamp that old I don't think I would spend any money on a repair unless you were really married to it, not worth it.

Thank you for your repleys ,