18-12-2016, 10:11 PM
Follow up to my last post.
The characteristics of the ECH21 are very similar to the ECH81 with the exception the former has higher Pa ratings. Ia is 3mA @ 250V. Ig2-g4 6.2mA @ 100V. Similar to the ECH81.
The attached circuit diagram shows the ECH21 operating as an IF amplifer and the triode as the audio amplifier. Negative bias for the triode sourced from the negative return of the HT supply. Also provides AVC delay. Can't find any more information for the heptode functioning as an RF or IF amplifier.
This information gleaned from the 1949 Mullard Valve Book.
Geordie McBoyne.
The characteristics of the ECH21 are very similar to the ECH81 with the exception the former has higher Pa ratings. Ia is 3mA @ 250V. Ig2-g4 6.2mA @ 100V. Similar to the ECH81.
The attached circuit diagram shows the ECH21 operating as an IF amplifer and the triode as the audio amplifier. Negative bias for the triode sourced from the negative return of the HT supply. Also provides AVC delay. Can't find any more information for the heptode functioning as an RF or IF amplifier.
This information gleaned from the 1949 Mullard Valve Book.
Geordie McBoyne.
