2 ohms=cold crt filament? (help)
John
8 volt line through about 8 ohms. The 8 volt line is 7.9. Clipping
across one of the series resistors (5.6 ohms) gets the voltage up to
about 5.8, and the thing brightens up quite a bit, although isn't
dazzling, and has a lot of red in it. The filament resistance is about
2-3 ohms (I checked it with a dvm without a low range so that's not a
very precise measurement.) comments on all this from the ng wizards
would be appreciated.
John
AJBCET
socket disconnected then with the socket on. note wether the RED cathode is the
same as the other two readings. you may have a bad gun, interna lshort are an
overall weak tube that needs rejuvenating. the resistance of a filament winding
is about 6 ohms each and you have three that are wired in parallel which will
read about what you measured(this is only the DC resistance of the winding).
make sure all three are lit. with the crt socket off place an ohmmeter on one
filament pin and measure the resistance to all other pins, there should be
continuity only to the other filament pin, all others should read infinity.
anthony
Sam Goldwasser
resistor?
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John
correct - I bought the thing used and someone had been working on it,
- but they look like they're original. I suppose that says the hot
resistance is that much higher than the cold resistance.
I need to take a look at the board to see what's between the two
resistors Some regulator thingy, I suppose, else they wouldn't have
used two resistors where one would do. The only schematic I have for a
modern 17" monitor, they use a series regulator to create 6.3 volts
off something higher, and have just a 1.5 ohm resistor between that
and the tube. Anyone with a similar schematic or knowledge of what I
should be looking for, I'd appreciate hearing from you. This is all
on the video board, by the way - they bring 8 V onto it and the
resistors I'm talking about are fairly near the tube socket.
Thanks, John
John
The filament pin shows 2.6 ohms approx to ground, and is shorted to
one other pin, the clockwise-most which doesn't have any ID
silkscreened on the video board. The pins are labelled, going CW, G1,
KG, G2, KA, H1, GND, KB, and no label. H1 is the heater, a bit more
than 2 ohms to the ground pin next to it, and shorted to the
unlabelled last pin. I haven't had a chance to look at the voltages.
John Del
nos...@tstonramp.com (John ) wrote:
> Thanks.
>
> The filament pin shows 2.6 ohms approx to ground, and is shorted to
> one other pin, the clockwise-most which doesn't have any ID
> silkscreened on the video board. The pins are labelled, going CW, G1,
> KG, G2, KA, H1, GND, KB, and no label. H1 is the heater, a bit more
> than 2 ohms to the ground pin next to it, and shorted to the
> unlabelled last pin. I haven't had a chance to look at the voltages.
>
Follow the fil circuit to the main board, and see if it is sourced from the
IHVT. If it is, make sure you are using a TRUE RMS DVM. If you are not,
typical readings for this type of high freq AC supply is 4.6 VAC at the tube
using a non true RMS meter.
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Terry DeWick
Most CRT's draw about 300 mA, a TV usually uses a FBT winding and
series resistor to filiment, most monitors are a bit more regulated
because they may have variable HV and seperate scan sections.
John
dog, if my reading of various postings is correct). The only schematic
I had was for a Sceptre P73, which put regulated DC on the filament,
so I assumed everyone did.