I've put together an Aikido 12VAC to use with 12AU7's, and when I bring it up to power on a Variac, the V4 tube glows bright red real quick. I've checked all components/connections and they seem to be correct, However, I'm not sure I have the jumpers J1 and J2 properly set up.
According to Broskie's instructions jumpers J1 and J2 should be used to ground the shield with 6DJ8's. He says: 'However using 0,1uf disc capacitors rather than jumpers will also ground the shield (in AC terms) and allow swapping in triodes whose pin-9 attaches to the center tap of its heater, such as the 12AU7.'
So, does this mean that I should be using 0.1 disc capacitors here or not using jumpers at all? I currently have the jumpers in place. 0.1 disc capacitors were not included in the glassware kit, so I just connected the jumpers directly. Might this be causing the problem with the glowing tube or is that not related?
My voltage readings with no tubes in are 51.3V for the heaters and a B+ of 156V, which is higher than the 148V it should be, so maybe my issue has nothing to do with jumpers and is all about getting a different resistor in the power supply to lower the B+. If so, can anyone help me calculate the correct value? I've got a 2K ohm 3W resistor for R12 and 20 ohm 3W for resistor R15.
Any help would be much appreciated!
PS: I've already built the 6DJ8 version of this preamp with zero issues, and I think this is a terrific, compact, easy to build preamp that sounds great. I wanted to use the 12AU7 version in my second system.
According to Broskie's instructions jumpers J1 and J2 should be used to ground the shield with 6DJ8's. He says: 'However using 0,1uf disc capacitors rather than jumpers will also ground the shield (in AC terms) and allow swapping in triodes whose pin-9 attaches to the center tap of its heater, such as the 12AU7.'
So, does this mean that I should be using 0.1 disc capacitors here or not using jumpers at all? I currently have the jumpers in place. 0.1 disc capacitors were not included in the glassware kit, so I just connected the jumpers directly. Might this be causing the problem with the glowing tube or is that not related?
My voltage readings with no tubes in are 51.3V for the heaters and a B+ of 156V, which is higher than the 148V it should be, so maybe my issue has nothing to do with jumpers and is all about getting a different resistor in the power supply to lower the B+. If so, can anyone help me calculate the correct value? I've got a 2K ohm 3W resistor for R12 and 20 ohm 3W for resistor R15.
Any help would be much appreciated!
PS: I've already built the 6DJ8 version of this preamp with zero issues, and I think this is a terrific, compact, easy to build preamp that sounds great. I wanted to use the 12AU7 version in my second system.
