18 watt PI problem
Moderators: pompeiisneaks, Colossal
18 watt PI problem
Newly constructed 18 watt lite II circuit. Vintage Sprauge bumblebee caps , 6v6 output with a 6sl7 PI. 300 ohm cathode resistor. My issue is one half of the PI is not loading down. Input plate side is loading down to 218 volts but the other side is staying at the B2 of 345 volts. If you hit the strings hard it volume swells from a low output and then drops back down. Pinouts for the 6sl7 have been checked multiple times. Pins 1 grid and 2 plate and pins 4 grid and 5 plate. Pins 3&6 cathode. Solder joints checked and reflowed. What could cause the PI to not load on the grounded input?
"It Happens"
Forrest Gump
Forrest Gump
Re: 18 watt PI problem
Have you tried a different tube?
Re: 18 watt PI problem
Success at last , thanks Merlin. According to Merlin The bypass cap on the second triode (in my case a .1 mf to ground) serves to pull the second triode out of phase with the first. Leave it out (or in my case , have a bad one) and the first triode will actually pull the second one into phase and you will get little to no sound. When I punched my strings hard the phases tried to pull apart , obviously , though failed horribly as evidenced by the distortion which occured. A good .1 cap later and she roars like a lion.
"It Happens"
Forrest Gump
Forrest Gump