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Old 01-15-2019, 02:09 PM
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3fp7 3rd anode

I'm looking for an idea for a power supply for the 3rd anode of a 3fp7 crt . I tried a small 3 kv neon power supply but the frequency is to high. I think something that takes in 120 volts would be good then I could use a diode to bring it to a half wave and that should work. Any ideas would be appreciated.
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Old 01-15-2019, 02:48 PM
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You know it's possible to drive a solid state flyback from around 20vdc with a power FET and an oscillator like a 555(I was able to get around 40kv with some experimenting)... lots of circuits for that in the plasma speaker hobbyist community. The 80s and newer flys have rectification of. the output built in.

If your CRT needs less than 10kv you might be able to use a smaller fly from a portable, less DC input voltage, the high current output of your 555, or some combination there of.
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Old 01-15-2019, 03:27 PM
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I do have a really small flyback from a 5 inch b and white tv but how to drive it and the pinout of the fly would be a problem I believe.
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Old 01-15-2019, 03:59 PM
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For openers, you could just tie it to the second anode voltage, which makes the tube a mono accelerator. Depending on what you are trying to view, that might be adequate.
Keep in mind that as you increase the voltage, the deflection sensitivity will decrease... you will get a brighter but smaller picture.

jr
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Old 01-15-2019, 04:07 PM
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Quote:
Originally Posted by jr_tech View Post
For openers, you could just tie it to the second anode voltage, which makes the tube a mono accelerator. Depending on what you are trying to view, that might be adequate.
Keep in mind that as you increase the voltage, the deflection sensitivity will decrease... you will get a brighter but smaller picture.

jr
Well this is an oscilloscope clock so I may be limited with voltage on the second anode.
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Old 01-18-2019, 10:35 PM
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What voltage does the scopeclock power supply give, or are you building that?

Not sure about tying things together. It can cause internal arcs if overdone.
------------------
3FP7, RMA data release #296, registration #296, 1942:

abs max voltages:
A3 4400
A2 2200
A1 1100
A2 to any deflecting electrode: 550V (there's the killer of scopeclock amplifiers)

Under typical operation, these values are given. (the file is too big to upload here)
A3 2000 / 3000 / 4000 volts
A2 2000 / 1500 / 2000 volts
A1 575 / 430 / 575 volts +20%,-35% for focus at 75% of grid voltage for cutoff
G1 -60 / -45 / -60 volts (visual cutoff)

A3 current 250uA at zero grid bias

============================
3FP7A, RMA data release #423, registration #859, 1945:

abs max voltages:
A3 4400
A2 & G2 2200
Ratio A3 to A2 voltage 2.3:1 max
A2 to any deflecting electrode: 550V peak

typical: (same as above)
A3 2000 / 3000 / 4000 volts
A2 2000 / 1500 / 2000 volts
A1 575 / 430 / 575 volts +20%,-35% for focus at 75% of grid voltage for cutoff
G1 -60 / -45 / -60 volts (visual cutoff)
A1 max current range: between -50 and +10uA

see attached schematic from datasheet
===========================

These informations came from the 'tube collectors' site, a CDROM is available with tons of tube data from the original registrations and updates, includes info often not seen in tube manuals. http://www.tubecollectors.org/announc.htm
It's also nice to have the huge bulk of tubes & older semiconductors, and an index, all in one folder. I recommend it!

HV supplies:
Some electronics gear has a self-contained PFC (power factor controller) board. It makes 400VDC, but on it can be had pulses to capacitively couple to a voltage multiplier. Any little line-operated switcher that's separate may work for this purpose as the current is so low.

I see you are doing a scopeclock. I love those, and put one together from time to time. Even though the old sparkfun board is no longer sold, the original Dutchtronix sells the blank board and through-hole parts kit for the generator, no power supplies though.

My aim if I can ever get away from the constant interruptions is to get an electromagnetic deflection unit going. There are 10" round radar type CRTs here, among other things like projection CRTs that can be seen in daylight.. other grails to chase..
Attached Images
File Type: png 3FP7circuit.png (104.3 KB, 8 views)
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