CTC-17 Screen control issue

[freakaftr8]

Hey Charlie. Actually the bright green raster is fixed. THis is a different issue.

[freakaftr8]

Ok so like I was pushing 250ma on the cathode current !! Yikes.. So I got her tuned down to 228ma give or take. Rhys the lowest it seems I can achieve at 25kv. Got my blue screen control back too. Nor to sure what I did yet but. Id works!! And looks decent too. These 17's seem to put out a nice pucture. I am playing with color alignment and convergence. I'll snap off a pic wiu a good raster in a bit.

[Bill R]

Think I would look a little farther into that cathode current. 228 is still a little high and a new flyback might be hard to find.

[freakaftr8]

I probably should start with the filter caps ? I'm thinking especially boost circuits. The sams says do not exced 230ma. My other ctc 17 is like in the 208ma area

[old_coot88]

Originally Posted by Bill R

Think I would look a little farther into that cathode current. 228 is still a little high and a new flyback might be hard to find.

Yes. You guys are probably already familiar with it, but there is a "last resort" trick in dealing with high cathode current on the HO tube. That's to get ahold of a few assorted 6KV disc ceramics of 68, 82, 100, and 120 pf or thereabouts, and, starting with the lowest value, clip it across the damper tube, direct from cathode to plate. This will drop the HO's K current a little bit. Then try the next higher value, which will drop the current a little more. A drop of 10-15 ma. should be possible. And the sweep width will increase. BUT as as with any trade-off there is no free lunch. The HV will drop concomitantly. Usually there is an acceptable "happy medium" that can be struck.

I've used this 'last resort' method to get a little more sweep in cases of insufficient width (it works on BW too. 4KV rating is sufficient in BW sets).

Also there were some flyback-eating 25" Admirals using the 6KD6 HO tube, where the K current would often exceed 400 ma. I also dropped the G2 voltage on the tube a bit, juggling it with the damper cap value, to get an acceptable trade-off between Kcurrent, HV and width.

[freakaftr8]

I messed with the cathode current a bit more last night. I'm not understanding when the SAMs states to short the sine wave coil. I shorted pin 8 to ground with no change in anything. I don't even know what to do with the sine wave coil. All I know about it is that it changes lock position across the horiz hold pots range. Also what does it mean to "float" the picture?I have 221ma now at 23kv and horiz width os just fine. I'm thinking my proceedure is wrong. I'm not shorting point H on the sync amp. I don't know what to short it too.
Think I'm stumped.

[old_coot88]

Please forgive my asking, but I didn't see it mentioned earlier in the thread. You did dip the hor. efficiency coil, right?

[freakaftr8]

I dont mind, ask away, I might learn something new.. Im confused when it comes to this proceedure. I did remove the shunt between pins 3 and 4 of the HOT and I do have a .47 cap across the leads now with a ma meter.

Dont mean to sound dumb, but what do you mean by dip the efficiency coil? I have adjusted the coil the best I can. Clockwise will advance the readings, ccw will decrease thwe reading. The reading is at the lowest it will go before it climbs again.. I know the proceedure states to advance 3 to 4 ma after you achieve this, but I left it at the lowest of 221ma.

Originally Posted by old_coot88

Please forgive my asking, but I didn't see it mentioned earlier in the thread. You did dip the hor. efficiency coil, right?

[bgadow]

Originally Posted by old_coot88

Yes. You guys are probably already familiar with it, but there is a "last resort" trick in dealing with high cathode current on the HO tube. That's to get ahold of a few assorted 6KV disc ceramics of 68, 82, 100, and 120 pf or thereabouts, and, starting with the lowest value, clip it across the damper tube, direct from cathode to plate. This will drop the HO's K current a little bit. Then try the next higher value, which will drop the current a little more. A drop of 10-15 ma. should be possible. And the sweep width will increase. BUT as as with any trade-off there is no free lunch. The HV will drop concomitantly. Usually there is an acceptable "happy medium" that can be struck.

I've used this 'last resort' method to get a little more sweep in cases of insufficient width (it works on BW too. 4KV rating is sufficient in BW sets).

Also there were some flyback-eating 25" Admirals using the 6KD6 HO tube, where the K current would often exceed 400 ma. I also dropped the G2 voltage on the tube a bit, juggling it with the damper cap value, to get an acceptable trade-off between Kcurrent, HV and width.

I, for one, had never heard this trick. I need to print it out because I have the feeling it will come in handy some day. In particular, I have an Admiral with HV problems.

[old_coot88]

Originally Posted by freakaftr8

... what do you mean by dip the efficiency coil? I have adjusted the coil the best I can. Clockwise will advance the readings, ccw will decrease thwe reading. The reading is at the lowest it will go before it climbs again.. I know the proceedure states to advance 3 to 4 ma after you achieve this, but I left it at the lowest of 221ma.

Then you've already "dipped" the coil for minimum current.

[freakaftr8]

Yes this sounds cool!

I got to figure it out. I have run this set for 4 hours tonight tweaking it.. It looks great! And I comared it to my other 17 tonight.. Take a look..

For some reason, my other 17 has a short horiz lock. It's finicky, not sure whats causing this but im surwe ill figure it out..

[ctc17]

Originally Posted by bgadow

I, for one, had never heard this trick. I need to print it out because I have the feeling it will come in handy some day. In particular, I have an Admiral with HV problems.

Yea this is solid gold. I saved it to my cathode current current web page info collection. I notice some of the zenith sets have this cap in place already. Would 15ma really make that big of a deal? I would have to calculate the wattage/heat that would generate.

[DaveWM]

I wonder if it has anything to do with the type of measuring equipment, I was going to try my DMM vs analog simpson next time I fire up my CTC 16, which IIRC is about 190. I wonder if the HO tube it self could drive up the current? gassy etc...


edit: that 190 was read with the DMM and 1uf bypass cap (did not have a .47 handy) and a 6JE6 tube. also using the orig filter caps (tested ok). That just seems like a big diff (190vs221). I would be real tempted to swap out the HOT just to see.

I think the HV was around 25k with a B&K HV prob, dont know how accurate they are.

[freakaftr8]

That's a really good question. Also could filter caps cause the cathode current to be high? I use a DMM rated max 400ma. I get reading from 221 to 241ma.

[ctc17]

Originally Posted by DaveWM

I wonder if it has anything to do with the type of measuring equipment, I was going to try my DMM vs analog simpson next time I fire up my CTC 16, which IIRC is about 190. I wonder if the HO tube it self could drive up the current? gassy etc...


edit: that 190 was read with the DMM and 1uf bypass cap (did not have a .47 handy) and a 6JE6 tube. also using the orig filter caps (tested ok). That just seems like a big diff (190vs221). I would be real tempted to swap out the HOT just to see.

I think the HV was around 25k with a B&K HV prob, dont know how accurate they are.

I have tried several different meters and they all read the same. As the tube ages the current goes down but it also looses the ability to supply enough hv on a bright picture.
As the horizontal drive tube/oscillator ages the cathode current goes up as the output tube looses drive.