Philco 48-2810

[TonyDuell]

The 'heating appliance' converters I've seen were a triac with a trigger circuit that causes said triac to be on for the right time to have the right RMS value of the output waveform. Not just a simple diode. About half a dozen components I think.

[julie_m]

Your 0.707 is wrong. A simple diode would give 240 * 0.5 = 120 volts, but all the pulses would have the same polarity. This DC offset could be problematic.

These sort of devices work by switching on at the middle of each half-cycle; giving half the energy from the crest and then half the energy from the trough, and averaging zero. This works reasonably well for simple resistive heating appliances -- hair styling devices, tungsten filament lamps, coffee makers &c. -- but is useless for some types of loads, and it can overstress insulation. In low-power mode, the appliance is powered from an autotransformer; which gives a nice, neat since wave, but power throughput is limited by the transformer.

[TonyDuell]

Originally Posted by julie_m

Your 0.707 is wrong. A simple diode would give 240 * 0.5 = 120 volts, but all the pulses would have the same polarity.

Would it?

Let's assume the load is a resistor (like a heating element). On 240V it dissipates a certain power. If you feed it half-wave rectified mains then it will, I think dissipate half that power (it's on for half the time it was on before).

But on 120V it would dissipate only a quarter the power (assuming the resistance is unchanged)

[usradcoll1]

Originally Posted by julie_m

Your 0.707 is wrong. A simple diode would give 240 * 0.5 = 120 volts, but all the pulses would have the same polarity. This DC offset could be problematic.

These sort of devices work by switching on at the middle of each half-cycle; giving half the energy from the crest and then half the energy from the trough, and averaging zero. This works reasonably well for simple resistive heating appliances -- hair styling devices, tungsten filament lamps, coffee makers &c. -- but is useless for some types of loads, and it can overstress insulation. In low-power mode, the appliance is powered from an autotransformer; which gives a nice, neat since wave, but power throughput is limited by the transformer.

My calculations of .707 should be spot-on. When using a diode for half-cycling that is the multiplier, the square root of .5= .707. It's referred to as RMS.

[Station X]

For a sine wave the RMS value is 0.707 times the peak value, but isn't 240V already an RMS value?

[ms660]

Yes, VRMS out = VRMS in*0.707, add the difference between in and out to the total heater string voltage and then subtract from VRMS in, then ohms law for any extra series resistance.

Lawrence.

[Station X]

Route Mean Cubed then? Or is it Route Mean to the power of 4?

[usradcoll1]

Originally Posted by TonyDuell

Would it?

Let's assume the load is a resistor (like a heating element). On 240V it dissipates a certain power. If you feed it half-wave rectified mains then it will, I think dissipate half that power (it's on for half the time it was on before).

But on 120V it would dissipate only a quarter the power (assuming the resistance is unchanged)

I measured the voltage across the resistive load in series with a diode dropper and it proves out to be 84 volts on our 120 volt mains.
The travel adaptors are designed to be used with our 120 volt heating devices, so when used with a triac type voltage dropper, it should produce the amount of heat the device is designed for.
I'm going to run a series of tests and see what this thing is about.
I have a transformer on my bench to step up our 120 volt mains to 240 volts. I have 120/240 volts in my building but the source is 50 feet away.

[Dick Glennon]

Hello again, I have another question.Ihave a transformer from an M.B 60.On the trader sheet it says that the secondary gives 105 volts. Would that be enough or would I have enough amps for the Philcoradio . Regards Dick.

[Dick Glennon]

Hi again, another question.? What were the set-studs that held on the card-back on the Philcoradio or can they be got anymore . Dick.

[usradcoll1]

Originally Posted by Dick Glennon

Hello again, I have another question.Ihave a transformer from an M.B 60.On the trader sheet it says that the secondary gives 105 volts. Would that be enough or would I have enough amps for the Philcoradio . Regards Dick.

The transformer would have to furnish about 35 watts @ 105 volts. The valves would take a little longer to heat up. HT should be close enough.
That's assuming the primary is rated at 240 volts. If you mains are a little higher, it would be a little better.

[ms660]

I'm not sure what's meant by an MB60 but if it's a Bush MB60 then forget it, not enough power.

Lawrence.

[usradcoll1]

Originally Posted by Dick Glennon

Hi again, another question.? What were the set-studs that held on the card-back on the Philcoradio or can they be got anymore . Dick.

Called "T" fasteners.
I have very few Philco radios of the era that still have the card back. They always got lost for some reason. I haven't seen those fasteners available for years.