Help with SE 6V6 bias/cathode resistor/cap values....
Posted: Sun 04/30/23 7:33 pm
Im building a MOD102+ with some modifications of my own. One of those mods is to add an extra octal socket for a 6V6 and wire it in parallel with the EL84 socket (minus each sockets cathode/pin 8 and 3 respectively) and then use a switch that lifts the cathode of one tube at a time in order to select one tube or the other. This is basically what the Mesa Boogie Blue Angel does.
Where im at is trying to calculate the bias resistor and bypass cap values for the 6V6. The best i could come up with so far was 470R/5w for the resistor and 25uF/100v for the capacitor. But these are just values I got from the Fender Champ schematic which isnt terribly dissimilar from the MOD102+ circuit. But id like some further confirmation about these values or some suggestions for better values. Id like the frequency response to be set the same for each output tube so that any differences im getting are from the tubes themselves rather than their bias.
And lastly i know that the 6V6 requires a higher input than the EL84 so if i dont change anything on the 6V6 input than there will be a slight volume drop when going from the El84 to the 6V6. So i was wondering if anyone had a suggestion about how to raise the input for the 6V6. I can figure out the switching part as long as i know what components should be changed and to what value. I suppose i could also attenuate the EL84 but id rather just have a volume difference than attenuate the EL84.
Thanks for the help! Below is the schematic for the MOD102+ with some of its voltages. And for good measure ill also add the layout.
Where im at is trying to calculate the bias resistor and bypass cap values for the 6V6. The best i could come up with so far was 470R/5w for the resistor and 25uF/100v for the capacitor. But these are just values I got from the Fender Champ schematic which isnt terribly dissimilar from the MOD102+ circuit. But id like some further confirmation about these values or some suggestions for better values. Id like the frequency response to be set the same for each output tube so that any differences im getting are from the tubes themselves rather than their bias.
And lastly i know that the 6V6 requires a higher input than the EL84 so if i dont change anything on the 6V6 input than there will be a slight volume drop when going from the El84 to the 6V6. So i was wondering if anyone had a suggestion about how to raise the input for the 6V6. I can figure out the switching part as long as i know what components should be changed and to what value. I suppose i could also attenuate the EL84 but id rather just have a volume difference than attenuate the EL84.
Thanks for the help! Below is the schematic for the MOD102+ with some of its voltages. And for good measure ill also add the layout.