05-15-2023, 10:56 AM
The 90 with a single 47 (second version, middle version or mid version) appears to be the most common of the three versions.
Correct, the early 90s with two 45 outputs do not have AVC. They operate in the same manner as an early model 70 as you said, only with two additional tubes in the audio section. The circuitry of the early 90 up through the 2nd detector is basically the same as the early 70. And, both use the plate detector circuit so they both suffer from the same distorted audio.
The "mid" 90 was improved by eliminating the 24 used as a plate detector, and using a 27 instead as a second detector, connected as a diode. They also added another intermediate stage of audio amplification. To keep the tube count at nine, the push-pull 45 output circuitry was changed to a single 47.
An early 90 isn't hard to tune, neither is an early 70 (or any radio without AVC for that matter). You just have to have one hand on the volume control knob if you live in an area with very strong local signals.
Correct, the early 90s with two 45 outputs do not have AVC. They operate in the same manner as an early model 70 as you said, only with two additional tubes in the audio section. The circuitry of the early 90 up through the 2nd detector is basically the same as the early 70. And, both use the plate detector circuit so they both suffer from the same distorted audio.
The "mid" 90 was improved by eliminating the 24 used as a plate detector, and using a 27 instead as a second detector, connected as a diode. They also added another intermediate stage of audio amplification. To keep the tube count at nine, the push-pull 45 output circuitry was changed to a single 47.
An early 90 isn't hard to tune, neither is an early 70 (or any radio without AVC for that matter). You just have to have one hand on the volume control knob if you live in an area with very strong local signals.
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Ron Ramirez
Ferdinand IN
