VINTAGE 1960's AUDIO TUBES

VINTAGE 1960's AUDIO TUBES Introduction

Anyone with 5965 tube experience? Back in the early 1960's there were many surplus military 5965's, They were used to replace both 12AU7 and 12AT7 types. The sound was really nice! Specifically using them in place of 12AT7's. The 12AV7, 12AT7, and 5965 are all different tubes with different MU, plate resistance and trans conductance. Check your tube manual! The 5965 is a "computer" tube, designed to be operated under "cut off" conditions for long periods. It seems like having large plates helps them to do this. Some single ended amps using 5965 as a driver tube in place of the 12AT7 sounds better! The 6201 is an industrial part number for the 12AT7. They will work just fine, but with a lower mu of 47 rather than a mu of 60 for the 12AT7. In general, feedback circuits take a sample of the output voltage and subtract it from the input signal. If open-loop gain is 100 and you feed back enough signal to reduce closed-loop gain to 10, then all distortions are reduced by a factor of 10. One of these distortions is gain error. If open-loop gain changes by 20% due to a tube with lower gain, for instance, then closed-loop gain changes by just 2%. There's more than one way to visualize negative feedback functionality. Think of it as being centred around the input stage where signal subtraction takes place, and that's often a differential amplifier. The output of this stage is a pre-distorted signal whose shape and amplitude is tailored to nullify errors introduced in all subsequent stages. The accuracy of error cancellation depends primarily on how much excess gain you can devote to this purpose. It's common in SS power amps to have 100 times or more gain than necessary (open-loop). When the loop is closed, distortions reduce to 1% of the open-loop values. The whole proposition hangs on one salient fact: Gain is cheap. Extra gain is about the cheapest thing you can possibly throw at the problem. In tube amps, gain isn't so cheap. You can still use 10x excess gain or a bit more, but phase shift in transformers generally prevents taking the feedback principle to extremes. Since each tube type has a different operating point, they will each work slightly differently in any particular circuit and one type may be preferred over another simply as a result of synergy with the circuit operating point. Good news: Negative feedback might not need re-calibration since a lower gain tube will generate less NFB. Payable by e-transfer No Paypal