Plans to build a CRT brightener?

[Airedale]

I've seen a few people talk about creating their own brightener, but haven't seen any plans for how they actually work.

It's just about increasing the filament voltage by about half, right?

Another mentioned you had to also increase the voltage to Grid 1.

I was gifted a VERY tired '89 RCA XL100 20". Even after adjusting the settings it is still rather dim. I figured that since this is pretty much garbage that I could experiment with it. If it blows, burns out, who cares?

If you know where to find the circuit design I'd be very appreciative.

[Electronic M]

In the vacuum tube era they were just a step up or boost wired autotransformer...There was no grid circuit change ( I don't think I have heard of that before).

They were rare by the solid state era.
Solid state era brighteners we're the same design but the transformers were different frequency.
Tube sets powered the CRT off 60Hz AC from a transformer or heater string, but most single board solid state sets powered the heater off a 15,750Hz winding on the flyback (so a 60Hz transformer wouldn't work).

In the last couple of years on a 2000's Sony HD CRT I needed to isolate the heater from ground, because I found an intermittent HK short that was causing shutdown. It was DC powered in the factory circuit, so I took a small 120VAC to 12V stepdown transformer, rectified it to DC, filtered that then fed it to an LM317 regulator configured as a 6.3V regulator (with the correct feedback resistors for that voltage) filtered that and fed it to the heater pins (I desoldered the socket pins from the board and pulled them out)...I figured out that a 6V relay I have draws around the same current as the CRT did so I hooked that relays coil to the factory heater supply (I think I have a reverse spike suppressor diode on the coil for safety) and used the relay contacts to switch on 120VAC to my home made supply. I'm still watching the set over a year later...
My scheme could be used as a brightener...All I need to do is adjust the feedback resistors that set the output voltage of the LM317 to increase the heater voltage and it would be a brightener.

You really should check what frequency of power your sets heater uses before you come up with a plan.

[zeno]

Good call E M

This set uses a FBT winding so at 15Kc's. They did make brightener /
isolation in the day,, just use the right kind.
2 tricks for basket cases.
1) there is almost always a one or two ohm resistor in series with the F.
Just jump it out, it will bring the F up to abt 8 V
2) On older sets with an open FBT core you can add one turn to
the F in series. This should be done with a scope so you dont
go too far.

73 Zeno
LFOD !

[Airedale]

Originally Posted by zeno

Good call E M

This set uses a FBT winding so at 15Kc's. They did make brightener /
isolation in the day,, just use the right kind.
2 tricks for basket cases.
1) there is almost always a one or two ohm resistor in series with the F.
Just jump it out, it will bring the F up to abt 8 V
2) On older sets with an open FBT core you can add one turn to
the F in series. This should be done with a scope so you dont
go too far.

73 Zeno
LFOD !

Jumping a resistor seems like a fairly easy way to increase the filament voltage.

So is their a difference between a FBT and an "open FBT core"? What does it mean to add a turn to the filament in series?

I have also come across an article on how to build your own basic CRT rejuvenator. If this increase in filament voltage does not bring about satisfactory results then perhaps an attempt would be worth it.

https://jestineyong.com/restoration-...uvenating-crt/

[dishdude]

You might be able to find a donor set with a good jug. I always liked that cabinet style.

[Airedale]

I just want to see if I can improve the brightness without sourcing a new tube.

This isn't a restoration, just me being bored. This is something that I can attempt to fix or mod but not have to worry over the fact that I'll probably mess up and fry it.

[zeno]

Yours should be a closed core. Open core will have a big donut
shaped HV winding & a small pulse winding. All is on 2 U shaped
ferrite core halfs held together by a U bolt. You would add one or 2
windings in series to the F near the pulse windings