finally got off my rear and replaced the RG static convergence pots. They were really fouled up, once I got them out of the circuit, one side was open and both had drifted a lot. there are some more pots in there, but I would rather not have to replace them as they are on a mount that is inside the chassis, with the dynamic coils mounted to the same. It would be a major pita. Since the chassis is so easy to pull I am just going to see how it works now.

I decided to open up the old pot, there was a break between the tap and one side, the pot wiper would complete the circuit when placed directly over the break, its hard to see but must be a crack.

Exactly the failure mode of the pots in mine. I think a poor design, too much current and pushing the technology to the limit to make a pot of only 100 ohms with a 25 ohm tap.

yep both pots opened in the 25 ohm section. Hopefully the new pots will hold up, I know I will not be putting the kind of hours on them they used to see when this tv was in regular service.

Got my fingers crossed for you - maybe they suffered from high contact resistance after getting dirty, so the new ones will last for a while?

I noticed one of the speaker plug in mounted to the fiber board on the speaker had come loose, so I pulled the speaker and fixed that. while I had it out I checked the 8mfd cap that is the crossover to the tweets. It checked at about 1 ohm on my simpson 260, both ways, so I dug around and found a sprauge atom 10uf 50v NP. I piggy backed it to the existing cap, clipped on lead so the old would be out of the circuit. the ne cap would quickly go to 700k ohms on the 260. I figure it prob will make no difference, but as long as I had it out I wanted to fix it. I also noted one of the two tweets has a lead broken where it mounts so I will have to pull it and see if I can fix. if not I have a few spares.

been slow to move on this, but I did replace the cap on the crossover and did fix the speaker fiberboard, and put it all back in. I have the chassis on the bench just need to get off my duff and put it back in the set and do a setup.

I am missing the two top pulls for the doors, a close up pic of them may help me find something that will be correct, those who have this set pls post a pic of the top pulls.

Curious: I had exactly the same failure on the red static convergence pot on my CTC5. There was a crack about a half way along the low resistance element end.

I do not think the pot suffered from electrical stress. I think the problem was with manufacturing and shrinkage of the carbon element over time. The break always seems to occur between the two rivets on the lower resistive portion to the tap simply because there are physically close together.

This evening I tried my fix: I went to "Canadian Tire" and picked up a rear window defroster repair kit. The kit includes conductive paint. I cleaned the pot element where the break occurred and painted a narrow band right over the crack.

After the paint dried, I reassembled the pot and it seemed to work fine. I checked the resistance of the previously broken section and it now measured 35 ohms, which is slightly low but about right. I then reinstalled the pot in the set and the static convergence adjustment now works okay.

Overall, I like the static adjustment on the front panel. But the pots are a pain. The design isn't bad: even though the static convergence voltage is derived from horizontal output plate current, any variations in current are mostly compensated for so that the convergence does not vary. It's just those bad pots. I would be just as happy to substitute the convergence clover leaf assembly with one which has permanent magnet adjustment, but that would be non-original.

I suspect the repaired pot should last a while until I can think of a better solution.

I made an interesting discovery today. I was troubled by the low grid bias on the horizontal output tube. This pointed to a slight reduction of horizontal drive.

I examined the circuit of the 6CG7 synchroguide horizontal oscillator. Comparing with the CTC7 and CTC9, the plate voltage of the oscillator was a bit lower.

To increase the drive, I thought I could raise the plate voltage a little. I discovered that R604 and R603 form a voltage divider. Further, I discovered my set had an 82K 1watt resistor for R603 where the schematic showed 100k. I tried substituting a higher resistance which raised the drive a bit. The offshoot is that the unregulated HV has gone up (good) and the grid bias on the horizontal output is now correct (very good).

Then after this, I read in the "Series 700 Setup-Service Manual" (available on at the ETF website), where, on the page 71 pictorial of the horizontal oscillator circuit board, there was a little note to the side of figure 132. It reads "Note: R603 may be reduced in value if less drive to horz. sweep output is desired".

So whadaya know?

Nice catch I will check that before I take the chassis off the bench :thmbsp:

glad to hear about the pot fix, i was wondering about how that conductive paint may work. I saved the bad pot after taking it apart, think I will try it as well.

reviewing the schematics I can see the ctc-5 has the 82k and the ctc-5N has the 100k for R603. I have a ctc-5N and it has the 82k, hmmmm.

the ctc-7 has a different setup, with a pot for drive adj, and a cap in series with the 100k/pot.

Question for Pentode, did you check the cathode current before and after the switch from 82k to 100k?

I had no evidence of a drive bar on my set so I may try changing the resistor if for no other reason to see if I can get that cathode current down. I still have to try it with with the new convergence pots so I can get a good reading in the cathode voltage of the horz out tube. It was high before, but I think that was just due to the increased resistance of the old pots. IIRC the called for cathode voltage is 7.5 v and I was at 12v. So will base line it with the new pots, get a revised cathode voltage, then experiment with the R603.

I did check the current (200ma) but the RCA schematic did not specify what it should be, just gave the cathode voltage. I suspect 200ma was about right but would like it to be a low as possible. I did adj the eff coil for the dip.

Don't bother worrying about it. The horizontal trans in my Wingate runs cool as a cucumber after hours of play time, and that's after I added pots for drive and HV to try and boost HV output. Most I ever saw out of it was around 22kv, I suspect the transformer itself and the way it's wound are holding back any more output potential. I think mine was around 200ma as well, but like I said it's not like it gets hot anyway.

Nick! Did you move all those sets out east with you.

I ended up selecting 110k. This yielded -40 volts on the Horizontal Output grid as per the schematic. The cathode current measured 210mA.


With 7.5 volts on the cathode, and the cathode resistance to ground at 23.5 ohms (the 82ohm in parallel with the static convergence 100ohm pots), this equals 320mA.

I now measure 5.0 volts for the 210mA. I increased the drive well below the appearance of the drive line. The HO tube runs a bit cooler and I have better regulated HV.

I only had room for the CT-100, 21-CT-55 and CTC-4. The rest are at my folks' house awaiting a chance for me to rescue them.

i check those two resistors in the plate circuit R603 and R604.

R603 is coded as an 82k which was on on the CTC-5 but shown as a 100k on the N chassis. I checked it out of the circuit and it had drifted up to about 94k so I left it alone.

the R604 which is coded as a 39k tested at 60k. Its 10% banded so I went ahead and replaced it with a 39k (tested at 41k) from my stash of old carbon comp resistors.

there was also a 1000pf cap that was from the junction of those two resistors to ground, If it leaked it would really mess things up, so I pulled it out and tested it. It tested perfect with no leakage so I put it back in. It was one of the red dominos, but I don't like to replace parts that check out perfect.

The only other caps in on the H board that were not replaced were a couple 82 pfs that were in the AFC circuit. As I was having no issues with sync I left them alone.

I really need to reinstall the chassis and see where I am just need to make some room in the shop as I don't want to work on it out in the garage.

With R604 now in tolerance, you should see more drive and the bias on the horizontal output higher. Please let us know the result.

will do.

I noticed in the RCA service manuals the CTC-5N had the 100k listed with 120k and 150k alternates. My plan is to try it as is (with the new 39k) and then try a 120k for the R603 (vs the 94k reading 82k resistor that is in there now.

all this time I have been saying I have the N chassis, I just double checked, its a AA chassis.

I did find raising the resistance slightly improved the HV supply slightly. But the increased drive may have slightly stretched the left side of the raster.

I think the problem is the back flyback HV supply design with limited beam current in this set. It would be nice to be told whether or not the CTC5 picture is as dim as other color sets of the same vintage.

CTC-4 is definitely brighter, but it also has a stiff 25kv anode supply. The later sets all had better horizontal sections as well, not as good as a 4 or 21-CT-55, but the 5 is the only odd one out of the whole early color RCA line with respect to HV generation. I still would like to one day sub a different anode supply into a 5, to see if more HV would make it perform as well as the others.

I think a few minor modifications to the sweep circuitry may be all that is required. I do not like the static convergence DC supply coming from the horizontal output cathode. Tying the cathode to ground and providing a separate DC supply might help. I expect there are other issues with the design as well.

I agree that the CTC5 seems the odd one out.

Like what? I already tried more drive, and removing the regulator tube completely. If I had to guess, it comes down to the flyback and how it's wound. If that's not it, there are still a few things to try. My 5N uses 5U4 vacuum tube rectifiers, swapping to solid state diodes to boost the B+ may help. I think the early CTC-7's were the last ones to use vacuum tubes for LV rectifiers, the rest had silicon. Might also try a solid state HV rectifier for more efficiency, but I hear they can cause issues like lines in the image on screen/video noise.

Not sure where else the convergence voltage could come from, you need it from the horizontal for the waveforms. Maybe a tap from the flyback would be a better choice, then the cathode could be more normal with just a resistor.

If you look at the CTC5 circuit diagram for the horizontal output tube, you will see that the cathode is heavily AC bypassed to ground. There is no signal on the Horizontal Output cathode. The voltage drop on the Horizontal output tube cathode resistances (100 ohm pots and the 82 ohm resistor) is purely DC for static convergence only.

I am suggesting tying the cathode to ground. This will in effect copy the later chassis' CTC7 onwards. I am curious if it is not the reactances in the cathode circuit which reduces the flyback pulse amplitude and makes the HV supply soggy?

As for the DC supply for the static convergence, I was was thinking of constructing a separate regulated DC supply. The DC would be derived from the filament supply. A suggested diagram is attached.

Certainly, simply ignoring the static convergence and simply grounding the Horizontal Output Tube cathode right at the socket would test the HV supply and I will be game to try it when next I pull the chassis.

Huh, I thought they pulled waveforms from there as well. It's been a while since I've been inside my Wingate, and I don't have it near me to play with it since I moved or I'd try it myself. Seems to me it would change the operating point of the output tube by a little bit, but probably not much. It would have the effect of driving the stage harder, since lowering the cathode voltage to ground would turn it 'on' more. But since the same thing can be achieved by the drive pot mod I already did (which accomplished nothing), I suspect the result will not be more HV output. Curiously though, I noticed that the 5 is not as prone to getting drive lines as the other chassis are. All these things are what leads me to believe that the transformer itself it what they changed, since it all leads back to that one part of the circuit.

I would expect the HO tube bias measured with respect to ground to rise by 5 or 6 volts when the cathode is grounded by virtue that the bias is derived by grid rectification. Hence the total bias is dependent upon the drive amplitude.

My thought is the added reactance to the cathode circuit (5ufd cap and wiring) may hinder the ability for th HO tube to be turned off at the end of forward scan. This would reduce the pulse height and inrease the effective series impedance of the HV supply. This is only my thought and I'd next like to explore.

getting there, I brought it in the shop, put the chassis back in and started setting it up (I had swapped in a replacement CRT, so I knew it would require a full setup)

In the process of adj the yoke for level I got bit pretty good. seems the outside of the CRT cover is not grounded very well. Perhaps thats just the way it is with these 21AXP22. I will confirm that all my grounding straps are in place on the CRT cover hold down AND the connection the the chassis is good. From what I can see the only connection to the chassis is a pressure connection from tabs on the front of the CRT mount that press into the chassis on the front.

I had a heck of a green neck shadow that I could not seem to correct without upsetting the purity. I never got the purity perfect anyway, I could get the red blob right in the cener with nice blue and green blobs around it, but when I moved the yoke forward I could not get a pure red screen, the bottom was the problem. I have not yet futz with the screen magnets nor tried degaussing (My 1st 21AXP22 set) so I will have to figure out how to adj the perimeter magnets so they are retracted and give it a proper degausse. This set is def a bit trickier than the later roundies I have worked on.

I need to get a handle on this hot yoke first. I did not try and measure it but the metal plate is def sparking up when grounded.

shoving the chassis up tight against the front of the set seems to have solved the grounding issue of the yoke, need to look into that a bit better. Maybe scuff up the chassis and the springs that make the contact and make sure all is clean. I am a little bit surprised there is not ground strap directly to the chassis.

I was not able to get the bezel out of the way, I can get the top out (the 3 spring clips that hold it in) and the side are not retained but the bottom is not budging. I looked at an old bezel that was loose and I see two holes that I assume fit over pegs on the bottom but can not say for sure.

Wingate owners please comment on how to remove.

while fussing with it I decided to check the voltage at the horz out fuse, was around 12v IIRC, now its more like 7.5 right on the money per the schematic

:yes:

during the intial setup I checked the blue screen purity (after getting the red as good as I could) the green was good but the blue was TERRIBLE.. I tried turning up the drive which helped but it was not just weak but more blue/green.

during a prelime setup of the center convergence I noticed the blue was way out, so I tweeked the blue lateraly, bingo blue not only converged but overall was much brighter. seems the blue lateral must have been causing the really bad purity also.

all this is just me messing about, I know I need to do a proper setup using the instructions which are a lot more complicated than what I have seen in other later roundies with later convergence boards.

Dave,

Remove the pencil box knobs. Remove the pencil box. This wll reveal, at the top of the opening, two spring loaded metal inserts that hold the bottom of the bezel in place. Take a small flat blade screwdriver and place into the insert and push down. You can do one at a time. This will release the insert from the bezel. Reverse the process when replacing the bezel.

-Steve D.

ah thanks Steve, One of them was missing the little metal clip, but I am pretty sure I can just pull it with some needle nose, the other one moved easy.

well the one missing the little clip is really in there tight, maybe that is why the clip is missing....

I don't want to damage the wood by a half ass approach with the needle nose so I will have to see if I can machine a tool to fit under the head of the pin and allow me to pull down. Dang so close.

got it with some hemostats, bezel out, glass out, magnets fully CCW so tomorrow I can do a degauss, thanks again to Steve for the hints. I hit the little mech with some lube so it should go easier next time.

I tried simply grounding the cathode. The was little difference. Perhaps a minor improvement but this was not the crux of the problem.

The CTC5 chassis seems to have HV issues. As Nick pointed out, it may have to do with the B supply. I noticed that as the brightness is advanced to blooming, the vertical scan increases (as would be expected with drooping HV) but the horizontal scan decreases. This suggests the horizontal sweep is has problems.

However, the HO Tube cathode current is low after I minimized it with the adjustment of the efficiency coil. I read elsewhere the that on another chassis the instructions called for a minimum adjustment and then the core was adjusted further into the coil to raise the HO Tube current to the correct value.

Any thoughts on this?

I will have to check the cathode current again. I did not check the line voltage, but the fly is getting pretty hot, and I do not seem to have any HV blooming (but I do have the video out contrast mod in). My concern is the heat in the fly HV tire. what currents are you seeing? are you checking the AC in and setting at 117v?

I bought several HO tubes to compare with.

My opinion at this point is that the flyback is wound in such a way that it is somehow current limited. In other words once you get to a certain point, perhaps the core begins to saturate. Can't do anything about that, because messing with the core (or its gaps) changes the magnetic properties of the entire transformer in possibly undesireable ways. Lets remember the whole transformer is a precision engineered part, especially with regard to frequency. Mess up one thing in any of the windings, and it goes haywire.

Or maybe the primary simply has too much resistance, since the amount of current supplied is influenced by the resistance of the primary. More primary resistance means less current when HO tube conducts, which means a weaker magnetic field and corresponding flyback pulse when the stage suddenly cuts off. Obvisouly, there is nothing short of rewinding the flyback that can cure it if that's the problem either. Folsom is the only one I know of that's tried (re?)winding one, and the results were less than satisfactory.

The secondary might not have enough turns in it, but that seems unlikely since it does in fact produce the required voltage at low brightness. That tells me the problem has more to do with the supply side of things, since the problem doesn't manifest till more demand is placed on it. It's not that there's a lack of HV per se, 21-22kv would be just fine for a 21" CRT. The problem is lack of adequite current delivery, which is why HV sags when brightness approaches normal viewing intensity- the beam current required by the picture tube outstrips the flybacks ability to produce it, so the picture blooms and lacks brightness. The situation is analagous to power grid sagging during the hot summer months, when everyone is running their AC units. Too much demand, and line voltage sags. The fact that the horizontal scan decreases in width is another clue, pointing to a lack in magnetic flux to power the scan coils. Again, I can only think of too much primary resistance being the cause.

If I'm right, about the only thing that's likely to make things better is an increase in B+ voltage. Since you can't get a load with less resistance, you can always try driving a larger waveform into it in an attempt to extract more power on the other side. This would likely require vast changes to the LV power supply, including a switch to solid state rectifiers and juggling the dropping resistors to all circuits besides horizontal scanning. Careful attention needs to be paid to cathode current in this case, since a small change in input voltage can push current way overboard in a hurry.

A good test would be to put the set on a variac, with the brightness set so that the picture just starts to bloom. At this point, you should be able to read a slight drop in HV. Try increasing the AC input voltage to say 125 from 117, and see if HV tries to come up at all. If it does, there may be something to investigate.

I was measuring about 210mA with the efficiency coil adjusted to minimize current. I believe the current should be a bit higher than this. The schematic inicates there should be 7 volts on the cathode with respect to ground. I measure 5.5 volts.

My thought is that adjusting the efficiency coil for slightly higher current will result in and increase to the unregulated HV. However, as Nick points out, the problem may relate to a limitation of the HV transformer.

I found the 6BK4 regulator is not really regulating the HV. This appears because the HV unregulated (with the 6BK4 cap off) is only about 23kV. When increasing the brightness hence the beam current in the CRT, the HV sags below 23kV.

Here is what I'd like to test: if the focus voltage does not track with the HV eg the focus voltage remain constant with the HV dropping, this means it is an unregulated HV supply issue. That is, the HV transformer is okay but the pulse to the HV rectifier is not of sufficient amplitude. If however the focus voltage also sags with the HV, then the HV transformer is likely at fault, as Nick suggests.

As for raising the B supply with a variac on the 117vac side, if the HV regulates better, that would suggest the former and not the latter.

Do you agree?

I was at 195ma, tweeked it just a bit to get to 190ma (simpson 260 VOM), solid 21kv with no noticeable flux on the HV meter (simpson 248 hv probe).

I am going to try some tube swaps just to see the effect with the current setup.


I don't have my good VTVM handy to get a control grid voltage reading on the HO tube, but will use my DMM and see what I get. Then will replace the 82k with a 120k in that voltage divider on the osc plate just to see if that will effect the drive/bias at that control grid (and perhaps further reduce the current thru the HOT). As long as I get good regulated HV I will see how low I can go.

I suspect some of the variations we are seeing is maybe do to the calibration of the test equipment?

matix balance pot (deluxe chassis) I get that is seems like a way to balance the gain of the X and Y demodulator tubes, but I could not find anything on how to set this up.

wow, new tube, gets me to 180ma and still good 21kv

yes pics coming soon :)