d5-100w crt
 

I have a d5-100w black and white crt I want to use in an oscilloscope clock it will work only problem is the heater voltage is .055 volts, .060 Ma so the question is the source on the clock board is 6.3 volts so would a resistor be able to take the voltage down to a half volt or maybe use a small transformer and use the 6.3 source on the primary of the small transformer. Any thoughts.... :scratch2:

If it is a DC heater source or you don't mind rectifying and filtering it an LM317 voltage regulator circuit should provide the most constant heater voltage.

It is an ac source right out of a transformer.

At 0.55V, could you use the drop across a forward biased silicon diode?

The lm317 regulator is 1.2v to 37v , not low enough, 0.55 , got to be carefull with this low voltage it wouldn't take much to burn the filiment. :sigh:

I'm not sure how to do the drop across biased silicon diode way even to see if it would work. Being I have 2 of these crts I would like to try in an oscilloscope clock. Be nice to have a black and white clock face rather then green. I had 3 but already burned the filiment out on one.

I am assuming that the heater is looking for 0.55v DC because the CRT was designed for battery operated portable TV's? An LT3080 regulator would fit the bill as it is adjustable down to 0v. You would need to rectify and filter the 6.3vac you have before feeding it to the regulator circuit.

So I'm assuming it's a positive reg , but I'm not sure how I would set it to put out .55 volts. I know I would have to rectify the 6.3 v and filter it befor injecting to the reg. The set pin ,is that for a pot or a resistor to ground ? Not sure here but it looks promising.

The 3080 I believe, only comes in surface mount. Not too sure you are comfortable working with SM parts. You can use the 317, just add 2 series diodes to the output and they will drop the extra voltage at the expense of regulation. Once you get it dialed in, the regulation won't be a problem.

So if I use the 317 I have to get it as low as possible which I think that regulator only goes down to 5 volts so at that point should I add several diodes in series until I get the correct voltage ? Because .55 is really nothing for voltage, lol.

The 317 goes down to 1.25 volts.

http://www.ti.com/lit/ds/symlink/lm317.pdf

1.25v - .7v = 0.55v

This d5-100w crt I have uses .55 volts however the datasheet don't specify ac or dc so I went and checked the tv that it comes from and to my amazement the heater voltage according to my DVOM is ac but here's the kicker, according to the datasheet the cathode is shared with the heater so how is this possible to even get an image with Ac on the heater.:scratch2:

I suspect that .55 volts of AC is quite small compared to the video signal, and just doesn't show up as a variation of the video.

jr