Just curious how much current is required in the deflection yoke coil for a
full scale displacement of the dot? Are we talking in the mA or A range
for a typical - let say ~20" - tube? I've seen vertical deflection
circuitry specs around 3A p-p. Does the yolk really require this much
current to reach full scale dot displacement for a sweep?

Trying to get a rough guestimate of measurement bandwidth should I use the
TV as an oscilloscope given the limitations of the voltage to current
circuitry. Was going to implement V to I circuitry using high voltage and
slew op-amps. It's not looking too hot - those coils really screw you. A
TV oscope - that makes no linearity adjustments and has no bells and
whistles - with a bandwidth in the 10's to 100's kHz is pretty crappy. If
the yoke current range is in the amp range, I'm really hosed - not that I
expected a high performance scope...


Thanks,

Monty

If you want to make a TV scope, you will be limited to the possible
timebase, because the effect of a physical magnetic field from such a
winding is limited in response to start with. The yoke core, and winding is
also designed to work at peak efficiency in the scan range that it was
designed to work in. This is the reason why scope tubes use deflection
plates, and not electromagnetic windings to make them have deflection.

The scans in the TV set have very fast rise times. This way, very high peak
current can be used. Depending on the particular yoke and deflection circuit
design, they are using about 2 to 4 Amperes to do the deflection. You are in
the proper range for the scan current. This however, is a very fast rise
time. The average current would be bit lower.

If you are using a TV CRT for a scope, don't expect more than a few hundred
kHz resolution at the very best. For the cost and effort, you can find some
very good used scopes around. Take in mind that when used, they are not
expensive in relation to their original purchase price. You may have to buy
two or three of them that are the same model, if they are older models, so
that you can have spare parts to keep one good one going. I have seen some
older descent 100 mHz scopes going for under 1000 US. The original purchase
prices for these were in the many thousands of dollars.

--

Jerry G.
======


"Monty Hall" wrote in message
m...
Just curious how much current is required in the deflection yoke coil for a
full scale displacement of the dot? Are we talking in the mA or A range
for a typical - let say ~20" - tube? I've seen vertical deflection
circuitry specs around 3A p-p. Does the yolk really require this much
current to reach full scale dot displacement for a sweep?

Trying to get a rough guestimate of measurement bandwidth should I use the
TV as an oscilloscope given the limitations of the voltage to current
circuitry. Was going to implement V to I circuitry using high voltage and
slew op-amps. It's not looking too hot - those coils really screw you. A
TV oscope - that makes no linearity adjustments and has no bells and
whistles - with a bandwidth in the 10's to 100's kHz is pretty crappy. If
the yoke current range is in the amp range, I'm really hosed - not that I
expected a high performance scope...


Thanks,

Monty

the vertical & horizontal should be the same so .......

on a old TV or turn the brightness down disconnect the vertical yoke and
connect to 0-30 volt power supply and measure the current.



"Monty Hall" wrote in message
m...
Just curious how much current is required in the deflection yoke coil for a
full scale displacement of the dot? Are we talking in the mA or A range
for a typical - let say ~20" - tube? I've seen vertical deflection
circuitry specs around 3A p-p. Does the yolk really require this much
current to reach full scale dot displacement for a sweep?

Trying to get a rough guestimate of measurement bandwidth should I use the
TV as an oscilloscope given the limitations of the voltage to current
circuitry. Was going to implement V to I circuitry using high voltage and
slew op-amps. It's not looking too hot - those coils really screw you. A
TV oscope - that makes no linearity adjustments and has no bells and
whistles - with a bandwidth in the 10's to 100's kHz is pretty crappy. If
the yoke current range is in the amp range, I'm really hosed - not that I
expected a high performance scope...


Thanks,

Monty

"Monty Hall" wrote in message
m...
Just curious how much current is required in the deflection yoke coil for
a
full scale displacement of the dot? Are we talking in the mA or A range
for a typical - let say ~20" - tube? I've seen vertical deflection
circuitry specs around 3A p-p. Does the yolk really require this much
current to reach full scale dot displacement for a sweep?

Trying to get a rough guestimate of measurement bandwidth should I use the
TV as an oscilloscope given the limitations of the voltage to current
circuitry. Was going to implement V to I circuitry using high voltage and
slew op-amps. It's not looking too hot - those coils really screw you. A
TV oscope - that makes no linearity adjustments and has no bells and
whistles - with a bandwidth in the 10's to 100's kHz is pretty crappy. If
the yoke current range is in the amp range, I'm really hosed - not that I
expected a high performance scope...


Thanks,

Monty



While this doesn't answer your question, I will say that if you just want a
cheap scope, pick up an old Heathkit, Eico or similar tube scope from Ebay
or a hamfest, you can get them for 10 bucks or less usually and the
performance while low by todays standards, will blow away anything you can
make from a TV.

"James Sweet" wrote in message
news:%JZyd.2924$Y57.1652@trnddc08...

| While this doesn't answer your question, I will say that if you just want
a
| cheap scope, pick up an old Heathkit, Eico or similar tube scope from Ebay
| or a hamfest, you can get them for 10 bucks or less usually and the
| performance while low by todays standards, will blow away anything you can
| make from a TV.

While they will be useable for basic TV servicing, a good scope can be had
on eBay for not much more than an old Eico type. For some reason they have
been selling for very little money in recent months - over supply I guess.

N