4 ms·

> The eye is especially useful because the AGC action tends to increase the audio volume of a mistuned station, so the volume varies relatively little as the tu

> The eye is especially useful because the AGC action tends to increase the audio volume of a mistuned station, so the volume varies relatively little as the tuning knob is turned. The tuning eye was driven by the AGC voltage rather than the audio signal. So, have a simple switch to disable AGC while tuning? Or, a not-so-simple switch. The switch could be linked to a pawl which engages the teeth of a gear on the shaft of the tuning knob, such that you can't turn the tuning knob if you don't activate the switch.

frrlpp 1mo ago
Not that easy, AGC works both ways, if you disable it you need to provide a manual control to not blow your speaker or your ears or both. AGC controls the screen voltage of some tubes with a big factor of amplification. A typical remote cutoff pentode like a 6sk7 can change some 30-40 dB for stage. 70-80 dB AGC action is not rare.
- kazinator 1mo ago
  > manual control to not blow your speaker or your ears or both. Distinct from the volume knob? It could be that rather than completely disabling AGC, it switches to milder compression. Another idea is that while tuning, we can delay the volume recovery of AGC. In other words, the same fast compression attack, but very slow release, so that as the user tunes across the center of the band, they can still feel the volume swell. A simple voltage divider could be introduced when AGC is turned off to attenuate the overall volume, so that the loudest blast is not that loud.
  - frrlpp 1mo ago
    AGC is not compression, is a negative feedback loop that reduces gain to maintain a relatively stable output level. If you try to tune on a faint station near strong ones, the stronger carrier pumps the gain down, making tuning difficult. if you cut AGC the gain goes full up. You can cut AGC and reduce gain, but then you'll lack amplification to hear the weak stations. If manual AGC and volume should be different controls depends on gain distribution across stages in the receiver. In superheterodyne AM receivers, most designs will need both to get best performance.

frrlpp 1mo ago

Not that easy, AGC works both ways, if you disable it you need to provide a manual control to not blow your speaker or your ears or both. AGC controls the screen voltage of some tubes with a big factor of amplification. A typical remote cutoff pentode like a 6sk7 can change some 30-40 dB for stage. 70-80 dB AGC action is not rare.

kazinator 1mo ago
> manual control to not blow your speaker or your ears or both. Distinct from the volume knob? It could be that rather than completely disabling AGC, it switches to milder compression. Another idea is that while tuning, we can delay the volume recovery of AGC. In other words, the same fast compression attack, but very slow release, so that as the user tunes across the center of the band, they can still feel the volume swell. A simple voltage divider could be introduced when AGC is turned off to attenuate the overall volume, so that the loudest blast is not that loud.
- frrlpp 1mo ago
  AGC is not compression, is a negative feedback loop that reduces gain to maintain a relatively stable output level. If you try to tune on a faint station near strong ones, the stronger carrier pumps the gain down, making tuning difficult. if you cut AGC the gain goes full up. You can cut AGC and reduce gain, but then you'll lack amplification to hear the weak stations. If manual AGC and volume should be different controls depends on gain distribution across stages in the receiver. In superheterodyne AM receivers, most designs will need both to get best performance.