04-11-2016, 11:22 PM
Yesterday I took a look at my KB radio. For starters it needs a replacement main dropper resistor. The total heater chain voltage is 114V and it works out for 240 volt mains the total value of the heater dropper will be 630 ohms. Dissipation is 25watts!
It's possible that the HT and heaters share the volts adjustable part of the dropper so the resistance values will have to altered to accommodates this.
About the set. It is a short superhet, that is the output across the detector load is supplied directly to the grid of a high slope output pentode, a Mazda PEN3520 in this set. I'd guess the intermediate frequency is low, say 128Kc/s, my reasoning being that a three gang tuning capacitor is used, indicates bandpass RF tuning.
Waveband changeover is accomplished by pushing in the tuning knob and turning it, neat job. Also, variable IF selectivity is a nice feature.
Much of the rubber wiring in the set is perished and needs replacing, chassis is a bit rusty but so what?
The pentagrid frequency changer valve is a Brimar 15D1 which heater volts apart resembles the American 6A8G.
The IF amplifier valve in my set is an ex-services VR106 = Brimar 9D2, apart from the heater volts the 9D2 = 6K7G.
Tomorrow I will make up some sort of mains dropper and tidy up the wiring.
Geordie McBoyne.
It's possible that the HT and heaters share the volts adjustable part of the dropper so the resistance values will have to altered to accommodates this.
About the set. It is a short superhet, that is the output across the detector load is supplied directly to the grid of a high slope output pentode, a Mazda PEN3520 in this set. I'd guess the intermediate frequency is low, say 128Kc/s, my reasoning being that a three gang tuning capacitor is used, indicates bandpass RF tuning.
Waveband changeover is accomplished by pushing in the tuning knob and turning it, neat job. Also, variable IF selectivity is a nice feature.
Much of the rubber wiring in the set is perished and needs replacing, chassis is a bit rusty but so what?
The pentagrid frequency changer valve is a Brimar 15D1 which heater volts apart resembles the American 6A8G.
The IF amplifier valve in my set is an ex-services VR106 = Brimar 9D2, apart from the heater volts the 9D2 = 6K7G.
Tomorrow I will make up some sort of mains dropper and tidy up the wiring.
Geordie McBoyne.
