18-12-2016, 09:33 PM
(This post was last modified: 18-12-2016, 09:35 PM by Geordie McBoyne.)
Only a limited amount of information for the ECH81 to hand because I'm writing this at home.
From the 1961 Mullard valve and tubes book:
Triode: Va 100. gm 2.8mA/V. u 22. ra 7.8Kohms. Ia 13.5mA.
Heptode: conversion conductance quoted. gc 0.75mA/V. ra 1.03Mohms.
Va 250. Ia 3.25mA.
The ECH81 is the successor of the ECH21 which was employed in many post-war Philips radios as the frequency changer and also employed as an IF amplifier with the triode section as the audio amplifier.
Both valves have a separate oscillator injection pin connection for G3. That pin is returned to cathode when used as an RF or IF amplifier.
One of the items donated to me by Wilfrid wiwior in France is a radio chassis in which the original side contact frequency changer valve has been replaced by an ECH81. Why would anyone want to do this?
The answer: looking through the pages of a Radio Bygones book I learn that the noise performance of the ECH81 is much better than any of it's predecessors. So it was a worthwhile valve substitution after all.
For the minimalist superhet I'm considering the Brimar developed 12AH8 for the frequency changer.
Reputed to be a very valve although the conversion conductance is not as good as the ECH81.
Geordie McBoyne.
From the 1961 Mullard valve and tubes book:
Triode: Va 100. gm 2.8mA/V. u 22. ra 7.8Kohms. Ia 13.5mA.
Heptode: conversion conductance quoted. gc 0.75mA/V. ra 1.03Mohms.
Va 250. Ia 3.25mA.
The ECH81 is the successor of the ECH21 which was employed in many post-war Philips radios as the frequency changer and also employed as an IF amplifier with the triode section as the audio amplifier.
Both valves have a separate oscillator injection pin connection for G3. That pin is returned to cathode when used as an RF or IF amplifier.
One of the items donated to me by Wilfrid wiwior in France is a radio chassis in which the original side contact frequency changer valve has been replaced by an ECH81. Why would anyone want to do this?
The answer: looking through the pages of a Radio Bygones book I learn that the noise performance of the ECH81 is much better than any of it's predecessors. So it was a worthwhile valve substitution after all.
For the minimalist superhet I'm considering the Brimar developed 12AH8 for the frequency changer.
Reputed to be a very valve although the conversion conductance is not as good as the ECH81.
Geordie McBoyne.
