protector fuse for ctc15 flyback

[timmy]

hey all where is the best place to put a fuse in the horiz circuit to protect the flyback from excessive MA. just incase of a failure and to many amps get to the flyback. i know its at the 6dq5 but i dont know what pin or wire at the tube to cut to put the fuse in between.

[Big Dave]

Tim,

Put the fuse in the cathode circuit of the 6DQ5. Use a 1/2 amp fuse. As of this writing, I don't remember the pinout. Use your print. I'll look up the tube tomorrow and get back to you..

[timmy]

just alittle confused as to what to cut and where to place the fuse. i looked at the sams but still little bit confused.

[jpdylon]

Find out what pin on the 6DQ5 is the cathode pin (I think its 4, but check!) Disconnect the line from that pin to chassis

Install the fuse holder in a normally accessible location. Connect one side of the fuse holder to the chassis, the other side to the cathode pin on the 6Dq5.

Install the appropriate fuse and you're ready to go.

[timmy]

ok the sams shows what looks like pins 3-6 then 7 is tied to the 3-6 going directly to ground and its marked 200ma, would this be where the fuse goes?

[timmy]

got another question, hv adjust pot has no affect and i have a new 6bk4 reg tube any ideas where i should go from there. possible i got a bad 6bk4? picture changes a bit when scenes change and i think there is poor hv regulation, bright down i have just about 24kv but if its not regulating on different picture changes then im sure ill have problems like i have now with vert not holding when the pic changes or just any change starts the roll and you can see the screen shrink just a bit on the changes.

[jpdylon]

The regulation on these sets is not all that great. The brightness going down on bright scenes is mostly due to the lack of full DC restoration. 24kv is just fine, try reducing the contrast slightly. Its not uncommon to get a little shrinkage on a bright scene. Shrinkage accompanied by loosing focus is often an indicator of a weak horizontal output tube and on occasion the damper.

These sets are not like newer CRT sets with well regulated HV and full DC restoration. You have to watch them in slightly darker rooms and not have light source hitting the face of the CRT.

If you have vertical problems, they wouldn't likely be caused by and HV problem. The two stages are not associated with each other - however the horizontal stage is directly associated with making high voltage.

post a snapshot of the horizontal output tube on the schematic, and I'll point it out. Its also helpful to have a receiving tube manual if you're having trouble reading the schematics.

[ctc17]

A few thoughts on this.

Flybacks usual failure mode is arcing in the secondary doughnut. My conclusion is this is due to wax loss and insulation failure from heat.

I leave the cage open on all my sets now and just avoid siting close to them. If you smoke or the set is in a dusty or humid area I would keep it closed.

Fuses are worthless because the thing runs and 200ma and the tube melts at 300ma. For this reason a 250ma chemical fuse must be used. (very hard to find) A regular AGC style fuse will have excessive drop and run hot eventually failing.

I have experimented with this and melted down the tubes never blowing the fuse. It may save you if the damper were to short or something catastrophic like that.

Lower the line voltage. This makes a HUGE difference in the amount of heat and life of everything. 108 seems to be a good number.

Dont stress it, those flybacks are substitutable with a little research and work.

[timmy]

well this set had the fly replaced and just wanted to protect it because these flys cannot be found anymore. and the horiz tube i had tried another one to see how things would be as far as hv adjust pot and still nothing. i dont loose brightness on picture changes just alittle shrink here and there with the changes,and the focus is ok as well. i just thought that when the picture changes that the hv could not keep up if its not regulating properly being the hv pot has no affect at all.

[ctc17]

Does that set have a CRT Bias switch or pot? Make sure its at minimum. (dimmest picture)
Follow the grey scale setup instructions in the sams exactly. If the bias, screens and drives are not set up right you will get the bouncing you speak of.

Try the HV adjustment at minimum brightness, does it do anything?

Horizontal blanking issues can cause the crt to 'overload' the high voltage below the threshold of the regulator kicking in. The Bias effects the blanking on that chassis.

I have a ctc11 on the bench and the HV is rock solid.

[timmy]

the grey scale is done and the hv pot dont work with the bright down, this set has a very good picture, colors, clear. all the tubes are new but i was just wondering why that pot did not work thinking it had something to do with the vert roll but when it warms up 15-20 min no more roll and it would seem like the vert tube 6em7 but tried another and the same result. the bias pot never had to be raised at all, the color set was right there,red,green,blue, lines.but the set does sometimes go into the horiz hold sometimes and have to adjust a few times also when it gets warmed up its fine. i also noticed the vert hold adjust in the front is close to one side of the adjustment, could it be i dont have the vert height and the vert lin set right and this is why the rolling keeps happening here?

[DavGoodlin]

One note about the 3A3 tubes used in the RCA sets from CTC16 to CTC39: Some replacement tubes were shorter and did not quite insert fully into the well of the flyback. This caused arcing due to the resulting gap. Sometimes it showed up as loss of horizontal sync due to the RFI generated. But worse, it caused many a flyback tracking meltdown in an RCA set. GE, Philco and others escaped this fate becuase only RCA used the upside-down tube flyback enclosure. The cure was to modify the enclosure cover's screw slots to allow the cover to be lowered sufficiently.

This was a tidbit from a veteran TV repairman I worked for in the 70's.