Does half heating equal half electricity usage ?

[Graham.]

Microwaves of that era had a proper length of waveguide do the radiation entered at the top of the cavity, and a rotating antenna distributed the energy around. A turntable wasn't that important, but some had one as well.

A squirrel-cage fan used the waveguide as a duct, and powered the rotating antenna pneumatically.

They were well designed and heavy.

These days the business end of the magnetron sits on a flange, and shines through a mica window, with the fan placed nearby in the hope it will provide a bit of a draught.

[Graham.]

Are you taking issue with what I said because I hadn't taken P.F into consideration?

I would have thought that as long as the core remained saturated, the power consumed would be independent of the conditions on the secondary side. Is that incorrect?

Also, as the anode of a microwave oven magnetron is its case, and it's firmly bolted to the chassis, wouldn't it be better to talk about cathode current?

[Capitol]

How does one run the core saturated without a bloody great bang?

[dennis]

You can heat a litre of water and measure the temperature rise to calculate how much useful power it outputs.

[Graham.]

I suppose the fact that it's only saturated for a proportion of each half-cycle. That also probebly explains where I went wrong in my assertion earlier.

[harry]

Ours is forty years old. (Thorn) Still works fine, fixed output, goes "ping". The timer knob needle has fell off and it's now yellow instead of white. ISTR it was £200 when bought.

[Graham.]

Our first one was a Plustron

In the shop it was actually cheaper than the basic clockwork timer one on display. I guess at the time,it wasn't selling well, as the average punter thought it needed a "Degree in rocket science" to operate it. How things have changed.

It was still working when I scrapped it 20 odd years later, and with all its original parts except the bulbs which failed regularly.

[Thomas Prufer]

You can't have a fractional turn, at least not without drilling thorough the core. And even then it's a full turn, but less flux.

Thomas Prufer

[tabbypurr]

If that were true, normal within spec mains overvoltage would prove a disaster.

NT

[tabbypurr]

Since lots of current flows through the filament, any talk of cathode current would confuse anode and filament currents.

NT

[tabbypurr]

70s nukes have unsafe interlock system and dodgy seals

NT

[tabbypurr]

I can certainly have a half turn.

NT

[dennis]

Thats about £2k now and that would buy you a very good microwave.

[Tim+]

And a bloody good feature that is! Nothing worse than "nagging" appliances.

Tim

[Thomas Prufer]

Either a winding encloses the core with the flux, or it doesn't. You can't half enlose it, and complete the circuit.

Thomas Prufer

[Peter Parry]

Dodgy seals? You mean the cabinet changed shape?

[tabbypurr]

I don't know what that means. Modern ovens use a choke seal, 1970s ones used a close fitting door with carbon loaded rubber strip to catch what got through. The strips are prone to going missing, and the system isn't so tolerant of door warpage.

The old interlock system is a far bigger issue.

NT

[Peter Parry]

Every domestic microwave oven since Amana introduced the table top microwave oven in 1967 has used a choke seal on the door. It is cheap, reliable, and maintenance free. There would be no reason to use anything else.

[tabbypurr]

Why then do 70s nukes use carbon loaded strips

NT

[dennis]

Why was the patent taken out in ~'82?

The capacitance seal pre-dated it but not by much AFAIK.