• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

12AQ5 SE Amp Issue

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
This is coherent with the thread title, and my question , I think, does not worth a whole new one, so
I build this :
It sounds Ok, but I never reach the 4.5 watt I was hoping for. It clearly clips at 3.2W (at the oscilloscope)
It seems to me, that the plate voltage is as high as it can be, so I blame the cheap PT-31 outputs. With new, better transformers, maybe it can reach the specs I want, what do You think?
Or I need to tweak the circuit itself?
Last edited:
Your topology is quite different, being, for one, a Single-Ended variety as opposed to Push Pull as mine is. What's more, you're not using a negative supply for the LTP bias. In short, this is an entirely different beast, and I wouldn't expect 4.5W out of it. As to tweaks, I can't really comment. Maybe someone else can.

I don't know the OPT you are using so can't really comment on it either. If the OPT doesn't have sufficient size it will saturate on low frequencies (where most of the energy is) and it won't perform well. So consider it's specs and consider upgrading if it's anywhere near the limit.
Something else to consider re: the OTP. It's rated at 8W, which sounds like it should be enough. But what is the frequency at which it's rated 8W? I can't find much about that OPT, but it looks like it may be for a guitar amp.

The low E on a guitar should be 82Hz, so if it's a guitar amp OPT, then it seems likely it's designed for that low end range and would saturate at lower frequencies at power levels less than 8W. And in general I try to run OPTs that are rated much higher than the expected output power (especially for a single-ended amp).

So in short, I suspect your OPT is limiting you. If you have a way to test a better OPT, I'd suggest doing that. I'm guessing you'd be quite surprised by the results.
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.