Pye 1107

[chompy1]

Hi All,

I want to replace R33 (820 ohm 1.3W), R35 (39 ohm 1.6W) and R38 (300 ohm 3W) with wire wound resistors.

Can I replace them with resistors that have higher wattage ratings?

Would resistors which have higher wattage ratings let too much amperage through?

Thanks in advance

[Silicon]

It is the resistance of the resistor and the voltage across it that determines the current through it. (Ohms Law).

For example, 30 Volts across a 300 ohm resistor will produce a current of 100mA.

The resistor will then dissipate 3 Watts of power (30Volts x 0.1 Amp).

A large 100W, a 3 Watt and a 1 Watt resistor will all dissipate the same power (as heat) but the resulting high temperature of the 1 watt resistor will probably result in its destruction.

Fitting a resistor with a higher wattage rating will do no harm and may improve the reliability of the device.

[ms660]

Originally Posted by chompy1

Hi All,

I want to replace R33 (820 ohm 1.3W), R35 (39 ohm 1.6W) and R38 (300 ohm 3W) with wire wound resistors.

Can I replace them with resistors that have higher wattage ratings?

Would resistors which have higher wattage ratings let too much amperage through?

Thanks in advance

1) Yes if you want to and they physically fit ok and they don't compromise any surrounding components in terms of heat.

2) Ohms law applies.

It's best if the rating in Watts is at least twice the calculated power dissipation.

Lawrence.

[chompy1]

Thanks chaps .

Lawrence, do you mean it would be best to replace R33 with a 3W, replace R35 with a 4W and replace R38 with a 6W?

[ms660]

Originally Posted by chompy1

Thanks chaps Lawrence, do you mean it would be best to replace R33 with a 3W, replace R35 with a 4W and replace R38 with a 6W?

If your calculations are correct then yes.

Lawrence.

[chompy1]

thanks Lawrence

[chompy1]

Morning All,

our mains voltage constantly flips between 232Vac - 237Vac and with this radio, I can always tell when the mains voltage drops to 232Vac, because the sound quality drops with it .

Would replacing R38 (300 ohms) with a 150 ohm resistor compensate for the fluctuations of the mains voltage?

Thanks

[Herald1360]

I wouldn't think so since R38 only affects the heater chain. Looking at its value vs mains voltage on the circuit suggest that maybe 220 ohms would be about right for your mains supply. 150 ohms probably won't do any harm, though.

[Mr 1936]

Hi

I would expect a set like this to easily shrug off a 5 volt variation in mains. I wonder if the UY85 halfwave HT rectifier is a bit tired, and the HT voltage is too low when the mains drops ? Try monitoring the HT with a DC voltmeter, using temporary wires soldered in so you don't get tired holding the probes !

Years ago my Grandma had an RGD deep 17 telly. The picture size gradually shrank over the years and became sensitive to mains voltage. With the oven on for Sunday roast, the picture shrank to the size of a matchbox and my Uncle complained that he couldn't watch the sport (he never was one for helping in the kitchen). A new PY33 rectifier solved the problem.

[paulsherwin]

Agreed, if you really can hear a difference with such a small voltage reduction then something is wrong. Are you sure you aren't imagining this? (No criticism implied - sound is very subjective.)

[Herald1360]

A 1N4007 or better the UF4007 variety temporarily in parallel with the UY85 would give a strong hint!