05-04-2016, 09:22 AM
Hi Gary,
thanks for the offer. That mains dropper resistor has to be replaced but first the original values of the sections must be determined, I'd like to return the set to it's original specification with the mains voltage tappings for 230, 200 and 110 volts. The total heater and HT currents flow through the dropper resistor, this is not normally good design practise. However, this set employs a thermistor in series with the heater chains so the valves are protected during the warm up period. Measured resistances of the thermistor are 1.8Kohms cold and about 200 ohms cold, those figures include the parallel resistor.
The 659 has two 0.1amp heater chains which add up to 84 volts each, that added to the the dial lamp and voltage drop across the thermistor we get 110 volts.
Hi Trevor,
there is only the 12 to 30 Mc/s waveband to sort out and that's the restoration of the RF circuits completed. The RF amplifier V1 should be an UAF41 or 42. In this set the previous repairer had fitted an UCH42. After checking the pin connections of both valves we find it is possible to get away by using the UCH42 as a substitute for the UAF42 and even the UF41. The UCH42 was found to be a noisy valve in the RF amplifier position.
The PL259 aerial socket has to go and it will be replaced with standard 4mm sockets for the earth and balanced aerial inputs.
Geordie McBoyne.
thanks for the offer. That mains dropper resistor has to be replaced but first the original values of the sections must be determined, I'd like to return the set to it's original specification with the mains voltage tappings for 230, 200 and 110 volts. The total heater and HT currents flow through the dropper resistor, this is not normally good design practise. However, this set employs a thermistor in series with the heater chains so the valves are protected during the warm up period. Measured resistances of the thermistor are 1.8Kohms cold and about 200 ohms cold, those figures include the parallel resistor.
The 659 has two 0.1amp heater chains which add up to 84 volts each, that added to the the dial lamp and voltage drop across the thermistor we get 110 volts.
Hi Trevor,
there is only the 12 to 30 Mc/s waveband to sort out and that's the restoration of the RF circuits completed. The RF amplifier V1 should be an UAF41 or 42. In this set the previous repairer had fitted an UCH42. After checking the pin connections of both valves we find it is possible to get away by using the UCH42 as a substitute for the UAF42 and even the UF41. The UCH42 was found to be a noisy valve in the RF amplifier position.
The PL259 aerial socket has to go and it will be replaced with standard 4mm sockets for the earth and balanced aerial inputs.
Geordie McBoyne.
