Re: Re: AX84 Variable Bias

[DeepBlue]

Thanks again B. I am just not sure what is going on here. So…well to be short things are still not working. I have played with resistor values and such for a bit now, as well as added my grid leak resistor, however I am still seeing my problem. So here is basically the situation, maybe I am missing something. i will also try to post some shots of my wiring, perhaps I have something wrong. So the Va is at 359V, which looks good and my cathode is is showing around 25V. These are both with the master volume completely turned up, which is a 1M pot. Now the problem is that with this spec, and the adjust bias pot set to 0R, the current is very high, around 180mA. So when I adjust the bias pot to bring the current down to spec my Cathode exceeds the voltage the bypass capacitor is rated for of 50V and the capacitor begins to smoke. Now the problem seems to be the range for when I adjust the master volume, that I can get the bias set, to around 62mA and the Cathode voltage to be around 25V when I have the master volume turned down, but as soon as I turn it up the values are way out of range. I am not sure if I have perhaps something wired wrong, as I have tried numerous values of the resistor for the cathode. I am currently at a 100ohm. I am also running a KT66 not a KT88 but I do not think this is the source of the problem, as I tried my KT88 originally cannot find a value that works for that tube as well. As a note for the bias I have been setting it to ( 25W * 0.9 / 359V). I am using a Shuguang KT66 Treasure. Sorry for the extensive email, but I am really not sure what is going on, as I see nothing wrong with my set up at this time. I will take a picture of the set up and post ASAP.