Rca CTC-25 overview and help

[ZenithNut]

Well I believe Im on the right trail diagnosing this problem. I have my nib sylvania 3a3c, a thordson nib horiz eff coil, and my hex tool. I was looking at the schematic thinking why after it warms up the cathode current becomes excessive. So I thought I should make sure everything between the horz oscillator and output tube is in order. I found a .01 cap going to the grid of the horz op tube. Said cap had broken solders. So Ive stuck a new .01 in place. Also I plucked the damper tube and noticed little cruddies shaking around in it. My precision 10-12 cant test compactrons without an adapter but I dont think little bits of crap jingling around in a tube is a good qaulity. I dont have another tube so I have not fired it up again to see if thats made a difference.

[DavGoodlin]

The damper tube may be OK but a 6DW4/6CJ3/6CK3/6CH3 is easy to find. I have too many. I scrapped many RCA's with bad flys over the years. It also sounds as if the 2AV2 is shorted, if it pegs the tester meter

Have you monitored the DC voltage on the 6JE6 grid? Usually the more negative it is, the lower cathode current would be. There are several .033-.068? caps across the horz eff coil too, which could cause it not to "dip" properly.

I have been able to lower the current in all post-CTC11 RCA's (not sure why yours increases beyond 220) by switching to the high line voltage tap on the power transformer primary.

[ZenithNut]

Originally Posted by DavGoodlin

The damper tube may be OK but a 6DW4/6CJ3/6CK3/6CH3 is easy to find. I have too many. I scrapped many RCA's with bad flys over the years. It also sounds as if the 2AV2 is shorted, if it pegs the tester meter

Have you monitored the DC voltage on the 6JE6 grid? Usually the more negative it is, the lower cathode current would be. There are several .033-.068? caps across the horz eff coil too, which could cause it not to "dip" properly.

I have been able to lower the current in all post-CTC11 RCA's (not sure why yours increases beyond 220) by switching to the high line voltage tap on the power transformer primary.

Dave and Electronic Memory a little bit of progress has been made!

I replaced one cap between the h osc and hor output, i replaced the hor eff coil I broke with a metal tool, now i have a plastic one . I replaced the 3a3 hv rect and 6bk4 shunt tube. Also subbed the 2av2. I swapped the damper and hor osc. I cleaned up the fire works show under the shunt tube. I hooked everything up and fed my nes into the vhf side of the tuner with a coaxial to uhf splitter.

Fired it up. This time as the hv comes up it goes between 200-240 ma instead of climing up to 300ma! I didnt have the anode cupped into the crt all the way and saw crazy high voltage. I shut it off and planted the cup in better.

So NOW theres still no sound, video, or vert/hor deflection BUT when you turn the set off theres a flash of something.

Also I can hear the hv forming around the cup of the flyback. Maybe I need to add another layer of silicon because it seems theres lots of corona forming.

Im afraid to keep it on longer than for the hv to come up because I dont know what its gonna do if I keep it on.

I will check voltages maybe with the hor output tube pulled out that way I can run it and check the B+ without being a nervous wreck.

I am happy to see the cathode current peak at 240ma instead of 300ma.

Edit: Ive been getting so worked up working on this thing I havent even checked B+ at the power supply or any screen voltages. Thinking of basic routine checks has been over shadowed by an almost fear/excitement combo. I will check B+, screen voltages, etc.

[Electronic M]

Good to hear you're making progress.

Definitely check your B+, h out screen and grid voltages, and report back...

Tip: if you have more than 1 meter you can grab multiple voltages at once with clip leads...if you have enough insulated color coded clip leads but only 1 meter, are careful and have plenty of cahoonies you can put a clip on every test point you care about and hot swap the meter... gotta be very careful not to touch anything conductive, but it can be done, and I have done it

Don't let the set freak you out of a logical state of mind.

[ZenithNut]

Originally Posted by Electronic M

Good to hear you're making progress.

Definitely check your B+, h out screen and grid voltages, and report back...

Tip: if you have more than 1 meter you can grab multiple voltages at once with clip leads...if you have enough insulated color coded clip leads but only 1 meter, are careful and have plenty of cahoonies you can put a clip on every test point you care about and hot swap the meter... gotta be very careful not to touch anything conductive, but it can be done, and I have done it

Don't let the set freak you out of a logical state of mind.

Thanks Tom. Its just because its a color tube set. I can play around with my tube zenith bw or my radios and fisher hifis and im a okay.

[ZenithNut]

[QUOTE=Electronic M;3207025]Good to hear you're making progress.

Definitely check your B+, h out screen and grid voltages, and report back...

Here are my results for measuring the B+ supply

Secondary winding ohmd out correctly at 7.3 ohms, 350VAC about 20v high.

Now the rest is just totally off.

B+ 1 455v

2 454v

3 436v

4 375v

5 372v.

6 288v

Its all jacked up. On pins 1-7 for the hor output grid theres 432v even though theres two resistors between the screen and B+ supply where its suppose to drop to 140v ! Pin 8 calls for -55v and its 27 volts positive. Dont get me started on how wrong the crt voltages are too.

I know bad E caps will cause low B+ but what about this?

[Electronic M]

B+ can safely vary by 30 percent in most tube TVs.

Your h out grid being positive instead of negative is very bad, and usually means your oscillator is dead or not feeding the grid. If the h out screen is high it usually means the plate is drawing far too much current.... this makes sense since if your grid is not negative enough plate current will be high(and positive grid will red plate the hot).

What I'd do in your shoes is disconnect the plate and screen of the h output and work on the osc until the output grid goes negative. The grid gets negative by rectifying the drive signal from the osc...if you unplug the grid or cathode of the output a negative voltage will not develop at the grid.

[ZenithNut]

Originally Posted by Electronic M

B+ can safely vary by 30 percent in most tube TVs.

Your h out grid being positive instead of negative is very bad, and usually means your oscillator is dead or not feeding the grid. If the h out screen is high it usually means the plate is drawing far too much current.... this makes sense since if your grid is not negative enough plate current will be high(and positive grid will red plate the hot).

What I'd do in your shoes is disconnect the plate and screen of the h output and work on the osc until the output grid goes negative. The grid gets negative by rectifying the drive signal from the osc...if you unplug the grid or cathode of the output a negative voltage will not develop at the grid.

Not sure I follow all the way. Disconnect the supressor grid and leave the grid thats supposed to be negative connected?

Also the b+ voltages are way off. Like for B+ 5 is supposed to be like 125v and its almost twice that. Its supposed to drop down ex 420 to 400 to 375 to 350 to 275 so on.

[ZenithNut]

So on 6je6 theres three grids which exact one do I disconnect along with the plate?. Im not surprised the osc isnt running because all those voltages are WAY off too

Also I took the voltage measurements for the h output with everything in place including the osc but none of the plate voltages or grid voltages are right.

[Electronic M]

I'd disconnect 1-7 and maybe pin 8...You could probably leave them connected for short powerups. The issue is that the screen grid will act like a plate if the plate is disconnected (or presents a higher resistance path, such as when the damper tube looses emission) and there will be screen current in excess of the dissapation specs damaging the tube on extended powerups.

The high B+ voltages are interesting. I no longer have a schematic for this chassis so without schematic voltage figure I can only gestimate how high the voltages are.

Be aware that the flyback is a large portion of the load on the B+ system, and when it is not drawing any current the B+ will be high. Also these sets have no B+ regulator circuits and expect around 115V input....If your line voltage is say 120V or higher, then that will also help push the B+ above spec.

The lower voltage rails may have reduced load on them from other circuits not drawing current...Vertical, audio out, and video amps are among the higher current loads on the lower B+ rails in most sets.

[ZenithNut]

Heres the power supply Tom.

I was wondering if it was necessary to have the tubes populated to load it down for accurate B+ checks. I had the chassis pulled with tubes populated and it was whinning so I pulled all the tubes to check b+ out of cabinet. I didnt know the fly was apart of that set up.

When I disconnect the screen should I repopulate the horinontal tubes or..?

[Electronic M]

My slightly annebriated new years troubleshooting advice:

You are right, some of your B+ voltages are well outside of tolerance, however those rails are derrived from other rails that are also not dead on spec (and things may not be loaded correctly) which may give GIGO data.

No tubes should be pulled with the H out screen and plate (the top lead connection) disconnected. The fly will not (or at least should not) be loading the B+ in this state. The flyback typically only loads the highest B+ rail (through the damper)...So if it is driving you nuts that all your B+ rails are high and you have a variac you can cheat your way to normalizing your B+....To do this connect a DMM to the 405V rail on your schematic and dial your variac till that rail reads 405V then you can accurately access how screwed up your lower voltage B+ rails and circuit voltages are*. This is probably the ideal state to do what you should focus on: Getting the H osc on frequency with test instruments, getting the osc amplitude and waveform up to spec and most importantly getting that signal delivered to the H output grid and developing negative H output grid voltage within 10% deviation of spec. Only when you have a decent approximation of correct H output grid voltage will it be safe to reconnect the H out plate and screen (that is a $25+ output tube so I don't advise running it outside of specs). When you have good H out grid drive you should be able to put the circuit back to stock connection and then have HV, horizontal sweep, and other working-set-like goodness (though shorts on the fly side could hamper much of that if present).

If the osc is not behaving and is powered by a lower B+ rail that is way out of spec even with variac normalization of the high B+, then what you should do is trouble shoot everything on that lower rail and try to get that rail properly loaded by working circuits.

*This may lower your heaters and make marginal tubes show their uglier sides.

[ZenithNut]

Originally Posted by Electronic M

My slightly annebriated new years troubleshooting advice:

You are right, some of your B+ voltages are well outside of tolerance, however those rails are derrived from other rails that are also not dead on spec (and things may not be loaded correctly) which may give GIGO data.

No tubes should be pulled with the H out screen and plate (the top lead connection) disconnected. The fly will not (or at least should not) be loading the B+ in this state. The flyback typically only loads the highest B+ rail (through the damper)...So if it is driving you nuts that all your B+ rails are high and you have a variac you can cheat your way to normalizing your B+....To do this connect a DMM to the 405V rail on your schematic and dial your variac till that rail reads 405V then you can accurately access how screwed up your lower voltage B+ rails and circuit voltages are*. This is probably the ideal state to do what you should focus on: Getting the H osc on frequency with test instruments, getting the osc amplitude and waveform up to spec and most importantly getting that signal delivered to the H output grid and developing negative H output grid voltage within 10% deviation of spec. Only when you have a decent approximation of correct H output grid voltage will it be safe to reconnect the H out plate and screen (that is a $25+ output tube so I don't advise running it outside of specs). When you have good H out grid drive you should be able to put the circuit back to stock connection and then have HV, horizontal sweep, and other working-set-like goodness (though shorts on the fly side could hamper much of that if present).

If the osc is not behaving and is powered by a lower B+ rail that is way out of spec even with variac normalization of the high B+, then what you should do is trouble shoot everything on that lower rail and try to get that rail properly loaded by working circuits.

*This may lower your heaters and make marginal tubes show their uglier sides.

I have the screen disconnected. So now I am going to populate the tubes, connect it all to the yoke etc. Then check my voltages with everything except the h output tube.

With no tubes as of now, I have 50 volts positive at the grid of the h osc. Instead of swinging negative it goes up to 80 v positive at pin 2-6 of the h output. I will plug the tubes in and all that and check again. Hopefully the tubes will load down the B+. Theres a hor waveform coil that is connected to the cathode of the h osc with a .01 cap in parallel with then it goes to ground.

[ZenithNut]

Alright,

So the reason the B+ was out of whack was from a 600 ohm 18 watt power resistor shorting internally. So instead of dropping 400v down to 350, it stayed 400.

With this corrected, I still have no sound or video. Grid 1 of the horz output is 55 volts positive.

[Electronic M]

Originally Posted by ZenithNut

Alright,

So the reason the B+ was out of whack was from a 600 ohm 18 watt power resistor shorting internally. So instead of dropping 400v down to 350, it stayed 400.

With this corrected, I still have no sound or video. Grid 1 of the horz output is 55 volts positive.

Probably time to turn your focus back to the horiz osc.