Ceriatone Forum

For any of you guys who want to run 6L6WGB's or 6V6's in your Overtone, but have been a little scared to, I have figure out a way to do so. I love the little 6L6WGB tubes due to their tightened bass response, and great all round mid and treble response, and find myself switching back to them often, especially since i now have the HRM post OD tonestack disconnected.

In order to use these tubes without modifying the Bias circuit is to knock down the Plate/B+ voltage. The reason for this is that in stock form, the bias adjustment circuit cannot adjust the current low enough to get a stable current load at a safe 70% dissipation rate. At Full Plate Voltage ( 447 volts on mine measure across Pins 3 & 8 ) the recommended 70% dissipation current rate is 40.7 mA. At full voltage with the stock bias adjustment circuit, it will only get down to about 42 ma, which is only about 2 mA above the 70% dissipation rating. i have run them at 50 mA with no redplating, but it is hard to get a clean sound at that high a current going through it, and they certainly won't last long like that, either. Many tube reviewers will say that these little tubes sound great at 50 mA (myself included), but again they won't last long.  Another problem is current creep. At high voltage, those little tubes tend to creep up at idle, so they won't stay where you want them.

To knock down the plate voltage, i use the Sag simulator resistor that Nik installed for me. It puts a 150 ohm cement block type resistor on the center tap of the HT taps. This drops the plate voltage down 20 volts, down to 427 volts on my amp. At this voltage rating, the current flow to achieve a 70% dissipation is 42.6 mA. This is easily achievable through the stock bias adjustment circuit, and it remains stable at this voltage as well.

All the 70% current rating numbers were figure through Weber's Boas calculator app @ http://www.webervst.com/tubes1/calcbias.htm

The addition of the Sag resistor switch is an easy one, and if any one has thought of using 6L6WGB's or even 6V6's in your Overtone, but have been a little gun shy, this might be the mod you have been looking for. Also, if you want to drop the voltage down even more to use older 6V6 types, you could add a large resistor value to knock the B+/Plate voltage down even more to allow safe usage of those tubes.

Hope this helps!!