I rarely post here but sure do value this community!
I am wondering (as I've had trouble figuring this out) if anyone could help with this. I have just enough tube/circuit knowledge to get in trouble and have been continuing to learn when possible. I've built maybe a dozen amps and finally can get most of them quiet now. Just to provide a little background on who you would be replying to. Intermediate/beginner here.
Attached (hopefully) is my schematic for the circuit in question. Please excuse the personal notes on brands etc. This is a plate reactor loaded 6sn7 with which I have limited B+ to work with. I am wondering about the voltage at the cathode resistor which is 7V. My DAC puts out 2v and my lineamp is unity gain. How can I figure out if I am in danger of clipping or if this operating setup is safe? I don't hear any problems but don't have a scope to test. I know that my cathode resistor value is higher than most at 1500 ohms but am very happy with the sound in this setup. Just don't want to damage anything. I experimented yesterday with raising the B+, lowering the cathode resistor value etc. but ultimately preferred the sound with the higher value cathode resistor (much tighter bass). This is the first time I have not used a resistor on the plate of the 6sn7. The 2 sections are paralleled (don't think I mentioned that on the schematic.) I am used to seeing closer to 2v at the cathode resistor.
I am wondering (as I've had trouble figuring this out) if anyone could help with this. I have just enough tube/circuit knowledge to get in trouble and have been continuing to learn when possible. I've built maybe a dozen amps and finally can get most of them quiet now. Just to provide a little background on who you would be replying to. Intermediate/beginner here.
Attached (hopefully) is my schematic for the circuit in question. Please excuse the personal notes on brands etc. This is a plate reactor loaded 6sn7 with which I have limited B+ to work with. I am wondering about the voltage at the cathode resistor which is 7V. My DAC puts out 2v and my lineamp is unity gain. How can I figure out if I am in danger of clipping or if this operating setup is safe? I don't hear any problems but don't have a scope to test. I know that my cathode resistor value is higher than most at 1500 ohms but am very happy with the sound in this setup. Just don't want to damage anything. I experimented yesterday with raising the B+, lowering the cathode resistor value etc. but ultimately preferred the sound with the higher value cathode resistor (much tighter bass). This is the first time I have not used a resistor on the plate of the 6sn7. The 2 sections are paralleled (don't think I mentioned that on the schematic.) I am used to seeing closer to 2v at the cathode resistor.
Keep in mind a bypassed cathode bias resistor increases even harmonics by up to 20db and because of the function of the human brain this sounds "wonderful " so it proves your human and not a bot.
No a 2V signal is not going to clip if you have 7V at the cathode. Yes it's operating safely at <1W dissipation. The cathode resistor does't have to be any specific value or range of values, it depends on biasing (what operating point you choose). If you're happy with the gain and distortion of that stage, you're good.
Thank you, Brice. I didn't know how to figure that out and it is super useful to know where that edge is!
No problem. The white curve is the grid/cathode voltage, that tells you the bias margin you have too.
