I’m looking to build a small simple ac voltage regulator with an input of a 6.3v filament transformer for the ac . problem is I’m looking for a voltage of .55v With the currant around the same as the transformer .60 but is there a way to put this together it has to be ac not dc. I’m not sure of what would be used and I know the dc regulators can’t be used. Maybe a triac? Anyone knows how to put something like this together please post it. I don’t know if a triac or an scr can go to that low voltage, .55v

What runs on .55 v ac? Does it need to be a clean sine wave?

What runs on .55 v ac? Does it need to be a clean sine wave?

Just needs to be .55ac it is for a d5-100 crt. It’s just for the heater.

The spec sheet doesn't specify AC or DC. Any reason why it has to be AC?

The spec sheet doesn't specify AC or DC. Any reason why it has to be AC?

I tried dc but it affected the clarity of the picture ac is better

Ah I see.

If it doesn't have to be a clean some you may be able to use TVS diodes (think Zener for AC applications), but I don't know if they go that low....ISTR from the pilot TV threads on ARF that to clamp the 3KP4 heaters at 6.3V they needed an 8.2V diode so maybe the peak VS RMS conversion might push the .55V up closer to something a TVS can do.

There is no easy answer for this, since this is such a odd CRT, with a weird heater voltage, most likely made to be used with a wire wrapped around a FBT, for power, ac voltage regulator circuits are rather tricky and complex to get right, one mistake a FOOM, your heater is dead.
One thing you may try is a rather hefty adjustable power resistor hooked to a 6v filament transformer and adjust the wiper up till you got the needed voltage, tricky bit will be choosing the value of the resistor.

There is no easy answer for this, since this is such a odd CRT, with a weird heater voltage, most likely made to be used with a wire wrapped around a FBT, for power, ac voltage regulator circuits are rather tricky and complex to get right, one mistake a FOOM, your heater is dead.
One thing you may try is a rather hefty adjustable power resistor hooked to a 6v filament transformer and adjust the wiper up till you got the needed voltage, tricky bit will be choosing the value of the resistor.

I already used a resistor with a 6.3v filament transformer but the transformer got extremely hot and I did get the .55v right on but the transformer won’t last.

I can’t use carbon resistors because there is no real load for the resistors to work .55v is nothing I used power resistors.

for example, a 1K Ohm adjustable power resistor 20-50w, should not load the transformer. hook it to the far ends, and the CRT to the adjustable wiper.

like seen here
https://www.google.com/imgres?imgurl=https%3A%2F%2Fwww.ohmite.com%2Fasset s%2Fcomponents%2Fphpthumbof%2Fcache%2FD100K5K0-updated.8d44712f18d06047506c409476db76f3.jpg&tbnid=ivKvKLfjlewG1M&vet=12ahUKEwjDuZ2OkPj-AhVYKN4AHbRQDfkQMygAegUIARDVAQ..i&imgrefurl=https%3A%2F%2Fwww.ohmite.com%2F210-series%2F&docid=xxIzEInteTMF3M&w=500&h=357&q=adjustable%20power%20resistor&ved=2ahUKEwjDuZ2OkPj-AhVYKN4AHbRQDfkQMygAegUIARDVAQ

You are basically using the adjustable power resistor as a voltage divider, that you can set to what ever point you need to.

A resistor with 20-50 watt it would have to get hot I don’t see how it wouldn’t load the transformer down as I can’t take a chance with this .55v like you said boom instant burn out. The voltage reading should show me .80v before I would put it to the heater which it would drop to anywhere from .450 to .530v

And the heater needs the current if not it won’t work I already had the perfect.55v but had no current to work

A 1k load on 6.3v is infinitesimal, smaller than most tubes, if by any chance the power resistor gets warm, try 5k or larger, I just pulled it at random, all that matters is there is something to divide 0-6.3 one end to the other on it, seems to me 1k should do fine.

The heater is 0.55 volts at 0.06A or 60mA. That is 0.03 watts.

You would need a 100 ohm resistor in series with the CRT filament to run it from a 6.3 VAC transformer. The resistor would put out 1/3 watt. Nothing should be getting warm at all.

Did you put a resistor in parallel with the filament instead of in series?

The heater is 0.55 volts at 0.06A or 60mA. That is 0.03 watts.

You would need a 100 ohm resistor in series with the CRT filament to run it from a 6.3 VAC transformer. The resistor would put out 1/3 watt. Nothing should be getting warm at all.

Did you put a resistor in parallel with the filament instead of in series?

A 100 ohm resistor would bring the voltage down to around .55v the wattage sounds good. Would that be a carbon or power resistor? The full voltage passes freely I have to be able to measure the voltage befor putting the heater on it otherwise it will burn the filament out instantly. I did put a resistor in parallel was the only way to get the correct voltage nothing in series would work.

The 6.3v transformer no load is around 8.50v with a 6.3v heater load it’s around 7v. But the ohms load of the .55v tube heater is 3.5 ohms

No wonder the transformer got so hot - you were basically shorting it out.

Saying 6.3 volt heater load is meaningless. What is the current or resistance?

Since this load is so light, better to adjust calculations for 8.5 volts.

(8.5 - 0.55)V / 0.06A = about 130 ohms. Wattage = (0.06 * 0.06) * 130 = 0.5.

Use a 1 watt resistor to be safe. Carbon comp, metal film, wirewound. Makes no difference.

No wonder the transformer got so hot - you were basically shorting it out.

Saying 6.3 volt heater load is meaningless. What is the current or resistance?

Since this load is so light, better to adjust calculations for 8.5 volts.

(8.5 - 0.55)V / 0.06A = about 130 ohms. Wattage = (0.06 * 0.06) * 130 = 0.5.

Use a 1 watt resistor to be safe. Carbon comp, metal film, wirewound. Makes no difference.

So if I use a 130 ohm resistor in series and then check the voltage it will show the full voltage at the resistor but putting it on the heater if it drops to where it should be what happens with the initial surge to the heater it could open ?

Well I tried it with 140 ohms and it brings it down but to 150mv the target voltage is .55v but before a load is placed it’s got full voltage but at the split second it’s put to the heater it could open the heater I believe.

The heater resistance on this tube is 3.4 ohms so I would use a 3.3ohm resistor to get a quick reference of the voltage befor plugging the tube in so the 150mv is to low 550mv would equal.55v but still full voltage for that split second I fear it wit take out the heater I only have 2 of these tubes that are good and I already burned the 3rd one I had.

The heater resistance on this tube is 3.4 ohms so I would use a 3.3ohm resistor to get a quick reference of the voltage befor plugging the tube in so the 150mv is to low 550mv would equal.55v but still full voltage for that split second I fear it wit take out the heater I only have 2 of these tubes that are good and I already burned the 3rd one I had.

That's cold I'm sure. as it heats up, the resistance in the heater will go up.

That's cold I'm sure. as it heats up, the resistance in the heater will go up.

Yes I’m sure it will but I need to know the initial surge voltage if any so the heater don’t open

Add a thermistor in series. They have the opposite property. High resistance when cold.

Does all this apply to dc as well ? Same result with the thermistor?

The way that Bandersen describing is one way to do this, the adjustable power resistor is another.

Using a resistor such as, https://www.digikey.com/en/products/detail/nte-electronics-inc/12WA210/11644319

Very cheap at under $7, and 1k won't put any real load on the filament transformer at all.
To be wired up like so, http://suzaku.live-evil.org/CRT-POWER.jpg
And starting with the resistor slider set to the lowest extreme, (0 volts) just slowly raise it up until you get the 0.55 volts you need on the heater for the tube.
This is how I'd do it anyway. :)

The way that Bandersen describing is one way to do this, the adjustable power resistor is another.

Using a resistor such as, https://www.digikey.com/en/products/detail/nte-electronics-inc/12WA210/11644319

Very cheap at under $7, and 1k won't put any real load on the filament transformer at all.
To be wired up like so, http://suzaku.live-evil.org/CRT-POWER.jpg
And starting with the resistor slider set to the lowest extreme, (0 volts) just slowly raise it up until you get the 0.55 volts you need on the heater for the tube.
This is how I'd do it anyway. :)L
So using the 1k adjustable resistor there may not be enough current and the question is would there be a large surge upon turning it on for a nano second which don’t take much to open a heater filament like this one @ only.55v ideally I would like to measure voltage & .830v then plug the tube in and see .50v or alittle more but I can’t do this because no load shows full voltage.

1k on the filament transformer places no noticeable load on it at all, especially with the heater being 3.4 ohms, with the CRT unhooked, the transformer and resistor should hardly get warm at all, and all power would go the crt when hooked up and adjusted right.

1k on the filament transformer places no noticeable load on it at all, especially with the heater being 3.4 ohms, with the CRT unhooked, the transformer and resistor should hardly get warm at all, and all power would go the crt when hooked up and adjusted right.
I know with the resistor in series the trans won’t get hot I’m not worried about that I’m worried about the crt heater opening if the resistor don’t react quick enough the heater will open.

This crts heater does not glow at the proper voltage

Ok 100 ohms was not good so I tried 200 ohms not good then tried 147ohms and I’m now getting.430v which will work maybe I’ll try to raise it alittle bit more to get it close to .52 or .53v the 100 ohm had a slight surge seeing the heater glow so that was not good.

The reason for all this is I managed to get a decent b&w picture on the pilot tv it’s a bit smaller then the green but it’s bright and clear so I needed to get this voltage right if it were to be played for any length of time. This crt is bearly used and I have a spare and should last, made in Germany.

Well I set up resistors for the target voltage which I had but I was using dc voltage so ac requires a lower ohm resistor 55 ohms for ac and about 150 for dc to reach target voltage that’s a big swing. Correction I screwed up it’s 143 ohms had to put 2 1/2watt resistors in series to get 1 watt brings voltage to .503v resistors get hot but not burning hot.