How do you set the bias on the Soldano SLO-100 head? I've had one for 6 months (IT IS AWESOME) and I'm gonn retube with some Slvetna (BTW: Buy them from SRS WEBSTORE at EBAY for unbelievalble prices) I've got a bias probe tool and was told by Soldano to set the bias at -56 to -58 volts, but WHERE? I used to set the bias on my Carvin legacy by measuring across the BYPASS switch. ANYONE KNOW??