15-06-2018, 03:34 PM
(This post was last modified: 15-06-2018, 03:35 PM by Geordie McBoyne.)
Hi Tracy,
You'll no doubt find many TRF construction projects in the 1950s Practical Wireless magazines. The type of volume control we are discussing was often used in contributors designs.
Getting back to the Premier Radio, the vari-mu RF amplifier valve's screen grid is now supplied from a potential divider. The upper resistor to HT is 27Kohms and the lower resistor is 40Kohms, (actually 18K and 22K resistors in series) The screen grid is decoupled by a 0.1mfd capacitor.
Doesn't seem to be any improvement in performance but at least the valve is operating according the specifications outlined in the Brimar valve book.
The anode bend detector valve is a 6J7. The slope of this valve is only 1.25mA/V. Any high slope pentode would be better but I don't know of any high slope valve in the international octal range with a top cap control grid connection. The Mazda SP61 has a high gm but has the Mazda octal base.
Geordie McBoyne.
You'll no doubt find many TRF construction projects in the 1950s Practical Wireless magazines. The type of volume control we are discussing was often used in contributors designs.
Getting back to the Premier Radio, the vari-mu RF amplifier valve's screen grid is now supplied from a potential divider. The upper resistor to HT is 27Kohms and the lower resistor is 40Kohms, (actually 18K and 22K resistors in series) The screen grid is decoupled by a 0.1mfd capacitor.
Doesn't seem to be any improvement in performance but at least the valve is operating according the specifications outlined in the Brimar valve book.
The anode bend detector valve is a 6J7. The slope of this valve is only 1.25mA/V. Any high slope pentode would be better but I don't know of any high slope valve in the international octal range with a top cap control grid connection. The Mazda SP61 has a high gm but has the Mazda octal base.
Geordie McBoyne.
