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LU9DCE > SYSOP 03.09.18 13:29l 208 Lines 4797 Bytes #999 (0) @ WW
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disconnect cathode &
retest. If still no voltage, disconnect diode, if AC appears suspect the
multi section diode. Do a cap test otherwise ( ÷ 1uF 3kV ).
c) if all OK except when cathode connected, replace magnetron/scrap.
d) if all OK, but no RF. Test heater circuit, no heaters replace
magnetron/scrap. Heater OK, test secondary circuit & repair connectors or
broken wire etc.
3/ If arcing noises or thumping are noticed, try checking in the dark, if there
is light from any connections/insulation take remedial action. If from
magnetron replace it. If radiator arc (RF O/P of magnetron), check the 1/4
wave cover is making good connection to valve pin if it is a separately
connected type.
4/ RF leakage. The RF is radiated into a fully welded box with 1/4 wave
overlaps door choke coupling. It should not leak much! But U can see the
100Hz FM bands on a 13cms CCTV Rx.
³³¬ Wave
COOLINGÚÄÄÄÄÄÄÄÄÄÄÄÄÄÙ³RF Seal
FAN ³ Magnetron |
³ Radiator o |see through
³ |mesh &
³ platter |glass door
³ =========== |
ÀÄÄÄÄÄÄ×ÄÄÄÄÄÄ¿³¬ Wave
Motor ³³RF Seal
I use a commercial microwave RF sniffer to make sure. It is crude thing
with a 10GHz diode & a meter.
MICROWAVE OVENS - PWR CALC. From: DAVID G4EBT @ GB7HUL
A magnetron's output power can be measured by checking the temperature rise in
øC of one litre of water during an 87 second period @ full output power.
A magnetron usually reaches full power about 4 seconds after the clock button
has been pressed, so the timer needs to be set for a 91 seconds test period.
If it's desired to determine the time lag from switch on to full power, use a
small neon with its wires cut off close to the pinch seal & insert it into the
oven cavity with the pot of water. It will glow brightly at full power &
shouldn't be left in after it starts to glow, or it may shatter.
The power output is given by the temp rise in degrees C x 50. Thus if there's a
14ø rise in temp of 1 litre of water over an 87 second period after the oven
has attained full power, the output power is 50 x 14 = 700W.
Another method, claimed to be more accurate, is to place two 500mL beakers of
water at equal temp in the oven, run the oven at full power for thirty seconds,
then check the temp rise in each beaker. Take an average of the two readings &
multiply this by 70 to get the output power figure.
The formula for this is given as: P=(4.187 x V x temp rise) / t
Where: P = Power in Watts.
V = Volume of water
t = Time of full magnetron power.
This test conforms to IEC 705 (1988).
This info is given in good faith (& at your risk!), from an article in April
1998 Television magazine, copyright of which is acknowledged. - G4EBT
HAM USE
I have seen a design for a 13cm ATV Tx based on a magnetron. A highly dangerous
project!
Many hams think the small but powerful 900W mains transformer could be useful
for valve linears. It can be done, but the trouble is one side of the 2.5kV AC
is wired to the transformer's case earth & even if that end was lifted off
earth, to feed a bridge rectifier to give a 3.5kV HT, the insulation to earth
of that end of the winding is poor & will not readily handle the 3.5kV peak! If
done a single 900W transformer should make a 800W continuous PSU or 1600W peak
CW/SSB mode PSU OK provided it is fan cooled as in the oven.
Another approach is to use a half wave rectification for 3.5kV DC PSU. But this
will DC saturate the transformer & reduces the rating by about a factor of 3,
making a 900W transformer only safely give 300W continuous with this amount of
core saturation & the much reduced inductance on the mains. So 2x identical
900W transformers wired in antiphase will be OK for QRO CW/SSB use. e.g. 600W
continuous load or 1.2kW intermittent.
OTHER DANGERS
WATER HOTTER THAN BOILING!
Note with RF heating it is possible to get water & some drinks actually hotter
than 100øC without boiling! This can occasionally happen if very clean
container & water are used, so clean that there are no crevices/particles for
the steam bubbles to from. Result is a cup of scalding liquid the boils over
at the slightest knock!
EXPLODING OVENS
If you are stupid enough to put a sealed container like an egg in the
microwave, it will explode causing a mess inside the oven.
If you are as stupid as those on a certain TV programme who put a new bottle
of champagne in one, it demolished the oven the table & the room, & certainly
might have killed anyone nearby!
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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