As SY said, the 12AX7 is quite linear when properly used. This means correct bias (avoiding cutoff and grid current) in a very high impedance circuit (load over 300K?). Not a valve which can just be slapped into any old circuit. The main problem is the high gain, leading to high Miller capacitance.
No, Morgan never tested 12AX7s. When I showed him my results, he wasn't at all surprised.
Maybe you're thinking of 12AU7? Morgan did test them and concluded that they were not fit for high fidelity use.
I'm just wondering how many of us in this diy community have actually seen (measurements) the harmonics characteristics of pre / amps we personally use. I see a lots of theories discussed but how do these thing perform in real life? I've measured both of my SET and P-P tube amps and they do show a difference that's in agreement with some posters here.
The key is the difference in measurement and how it manifests itself in audible sound or not.
Not strange at all. You would expect distortion of a few % just below clipping, which is barely audible and better than some loudspeakers. Provided the bias is correct this will be mainly low order. Add feedback to get it down to 0.1% if you wish.
When I first built my modified 5-20 I listened to it open-loop before debugging the feedback. Open-loop it was quite pleasant to listen to, apart from lack of damping as you said. I could therefore be sure my feedback was improving a good amp, not patching up a bad amp.
When I first built my modified 5-20 I listened to it open-loop before debugging the feedback. Open-loop it was quite pleasant to listen to, apart from lack of damping as you said. I could therefore be sure my feedback was improving a good amp, not patching up a bad amp.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.