I had a tube in the PI and scoping it, I got a signal out on each side where one side was double the amplitude than the other. I don't remember the numbers right now but lets say 20V pp on one side and 40V pp on the other. The plate voltages on each side (100k/100k) were 212 and 220. So the tube was getting approximately the same voltage but the output was way off.
I took this tube out and swapped it with V2 which is just a single gain stage, and all was well again.
Is this tube, a 12ax7, starting to go bad, or are some tubes just way way unbalanced?
PI output totally different
Moderators: pompeiisneaks, Colossal
Re: PI output totally different
What's the cathode current on each side, assuming Rk is the same value and Va is about the same? I think you are going to find that the tube is not balanced and maybe one side is nearly used up.
I think you know to calc cathode current based on Ohms law, the voltage, and the value of Rk.
The tube may be satisfactory as a quirky gain hole tube, just not as a PI.
I think you know to calc cathode current based on Ohms law, the voltage, and the value of Rk.
The tube may be satisfactory as a quirky gain hole tube, just not as a PI.
Re: PI output totally different
yea, that's why I moved it over so even if the gain started falling it wouldn't affect the split signal. I didn't measure current on the cathode as the PI has the shared cathode and I didn't want to solder any more tonight.