CTC-17 Screen control issue
 

Hey guys,
I picked up this CTC-17 combo last month and after changing like darn near every tube in the set as it seems it was a high use set I got HV and accompinied by a bright green raster, after replacing a broken wire I have barely any blue screen voltage. The CRT is good but I have been looking at the chassis and I cannot seem to figure this one out.. Any ideas?
Thanks!

Did you have the sams on this one? I will take a look when i get home and can scan it if you need.

Oh yeah I have a sams. I had to repair the CRT socket. Bad corrosion and some arcing on the focus pin. Thought this might have been an issue as well but it's not. If i pull the B/Y 6GU7, I have good blue screen drive voltage. Max should be 177v. I get about 70v, green and red max around 177 to 180v. Im suspecting im looking over an out of tolerance resistor somewhere.

Any chance the crt is leaking and loading that voltage down? I would be interested in seeing a picture, I bet we have almost the same exact combo. Mine has a really good picture better than my Zenith sets.

I know these 17's put out an amazing picture! Dont think the CRT would be an issue, I get full voltage to the CRT when I pull the B/Y 6GU7 amp

I would be interested in the voltages on pin 6, 7 and 8. If c140 was leaky that could do it for sure. Or if r198 had gone way up in value that would do it too. With the tube plugged in I would 'feel' r198 to see if its super hot like the tube is biased on and loading the resistor down. If r196 were open I suspect it could cause the tube to bias on load that voltage down too.

For some reason someone circled that resistor on my copy of the sams.....

Ok here's something else.. I just checked the HOT cathode current... 112ma?? Thats low and I bet this is a cause of the excessive wax all over the bottom of the chassis

Here are pics

All 3 of my rcas have wax. I dont think I would stress that. That is kinda low though but I dont see how it could effect this blue drive thing unless the 400volt boost was low for some reason. That almost seems like a false measurement.

Have you checked the hv on the crt?

This is my first one.. Got this one in November 2008

http://i739.photobucket.com/albums/x...9/IMG_0306.jpg

And here is my CL find in downtown Sacramento. This is the one im talking about..

http://i739.photobucket.com/albums/x...9/IMG_0305.jpg

Hmmm, im going to check my filters.. Good call! It just seems that this one has an excessive amount of wax, my other 17 (the first one in the pics) has no wax droppings at all..

I always thought that the rule of thumb was if you have too high current on the fly it will overheat and damage it and the same goes for too low current as well. my other 17 is around 208ma (which is pretty good as current goes).

Mine looks different. Someone cut the legs off mine long ago this is and issue because it cant get air up through the bottom. I put a muffin fan to take care of that though.

I have 2 of these with the rca tuner and I have never been able to get the stereo multiplexer aligned right. If I get it aligned to where the separation is correct the noise floor is so high its annoying. I can get it half way in between but its fake stereo.

The Zenith receiver seems superior and the rca tv seems superior to the Zenith. Maybe a mashup is a good idea... ok Im off topic here.

I know what you mean about the multiplexer. This new ctc17 I have seems to have that same issue. It's the 800 series. It seems to have more right channel output than left.. All in good time. At least the stereo works.. The one on the other 17 wouldnt work right. I replaced all the outputs and it worked fabulous! It's the 400 series.

Hey ctc17, post up a pic of your set, with or without legs, im sure it's nice

I have a cell phone that has an fm stereo transmitter in it. I made an mp3 that plays in the left channel only for a few minutes then the right only for a few. The sams gives and alignment procedure for using a strong fm signal. I can get the separation right but its totally noisy.
Come to think of it I cant thing of any tube multiplexer I have seen that worked real good.

The receiver im mine totally died now.

Its NOT nice! Its poor and even has cigarette burns in it. I found it on the curb in the hood. Give me a few let me get a pix..

http://justsmog.com/Clay/ctc17.jpg
http://justsmog.com/Clay/ctc172.jpg

Freak, I have a 15 that had issues with that bright green screen. Turned out one of those 6GU7's just wasn't seating good enough in the tube socket.

Just curious... what kind of line do you get when you slide the service/normal switch to the service position?

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

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.

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.

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

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 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.

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

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.

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.

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

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..

http://i739.photobucket.com/albums/x...9/IMG_0316.jpg
http://i739.photobucket.com/albums/x...9/IMG_0315.jpg

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.

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.

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.

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.

Oh yes indeed. The 6JE6 is already being driven to the max with virtually no "headroom" for overcurrent. It may be happy at 210ma but 225ma can spell doom. If the flyback doesn't fry first, what usually happens is- a hot spot develops in the glass of the 6JE6 which softens and sucks in at that spot. The tube goes to air in an instant, shorts out and kicks the breaker. Hopefully someone has not replaced the breaker with one of higher rating. I've seen sets come in with 7 amp breakers in place of the original.

If the tube is running at 221ma, keep a close eye on it and watch for any cherry red areas developing on the plate. Above all, NEVER, ever leave a vintage color set running unattended (even one with no overcurrent issues).

Also, if that set still has the original RCA flyback, it would be wise to watch it close. Seems the originals were crap to begin with. If you compare the original to a replacement, you can tell the replacements were built like brick shit-houses!

Not necessarily. The first sign of the H.osc tube going weak is that the osc. will be off-frequency when the set comes on from a cold start; it'll take a little time for the lines to straighten up and the pic to lock in. A quickie test of the H.osc tube is to turn the set off for several seconds, then back on. If it comes on with lines before locking in, the tube is getting a little weak. If it comes on fully locked, the tube is good. A weak osc tube will generally cause off-frequency problems before drive level to the HO tube is affected.

By "short", do you mean weak/touchy? If so, have you replaced the phasing diode? 95% of the time, weak horiz. sync is caused by that dual diode going bad. IIRC, it is common-cathode (not series) type.

Oh duh. Your spot on old coot88. I had his issue on a magnavox. I'm going ro replace it.

Don't see how. Bad power supply filters would show up as hum bars or "bend bars" slowly creeping up through the picture.
I would get another meter, preferably analog, to double check that current. Digital meters can go nuts if there's any strange waveforms present in what they're trying to measure. There's a helluva lot of horizontal sawtooth and even RF in that current, and even if you have a cap across the meter, some of that stuff can still get past it.

If the current is really running that high, the tube is gonna be sizzling hot. Old techies could tell if the tube was running too hot just by holding the back of a hand next to it.

Try adjusting the hv adjustment for a dip. I remember a specific point where the hot current dipped in the hv adjustment. It may have been 500volts off from 25k but I was looking for the lowest current.

I was thinking more of the Zenith setup with the tipple triode that gets weak and cause lack of drive.
Im interested in the cap/damper trick. I may try that on a few of my sets.

Yrp youre right. The current does dip with hv adjustment. Im like 24000 at 221ma, at 25kv 240ma. Im going to give this theory that old coot88 had with the pf caps across the cathode-plate.

But first im going to try a different meter, probablyt an analog simpson from work first. Ill see what I can come up with and let you know.

The only problem with adding caps is that the set was not designed that way and you could be just masking the real problem. I would exhaust all componant checks first. Then if all else fails and as a last resort I would add the caps. I doubt the meter would make much difference, and a good digital meter would be easier to read and interpret thus more accurate results. A good meter not the $1.99 special from the tool store. For the most part you get what you pay for.