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Old 01-20-2004, 06:52 AM
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Chad Hauris Chad Hauris is offline
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Horizontal output cathode current/flyback overheat

I've got 2 round color sets, a GE and a Wards, that are based on the CTC-16 chassis. I have been noticing a smell like an overheated flyback recently. The flyback compartment door is hot. I have checked the horiz output, damper, HV rect. and regulator tubes. The sets otherwise appear to operate OK.

These sets have been modified to include a 1/4 amp horiz output cathode fuse. The fuse blows very gently after the set has been on for a 1/2 hour indicating that cathode current may be around 260 ma (which is probably too much).

However when I use my digital multimeter to measure current I only come up with 20 ma current. Could my meter be bad? Anyone else measure this with a digital multimeter successfully?
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Old 01-20-2004, 10:31 AM
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Last edited by andy; 12-05-2021 at 09:23 PM.
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Old 01-20-2004, 10:51 AM
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Andy, thanks for suggestions...I did try using a .47 cap across the meter leads when I took the reading, but just got the erroneous 20 ma reading...yes I did disconnect the fuse, breaking the circuit, and hooked the meter leads one to the cathode terminal and the other to ground.

May need to just go out and get an analog VOM for the job. Also have heard about putting a 6.3 v. lamp in series w/ the plate lead to adjust the current...I might try that.

Last edited by Chad Hauris; 01-20-2004 at 10:53 AM.
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Old 01-20-2004, 09:38 PM
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ctc 16

Hi Chad,

The ctc16 uses the 6JS6 H.O. and should be running cool at 220ma. Basically, ho tubes should be withing a range of 180-220. 260ma is burning bad. Since its based on a ctc16, there is a major component(s) that needs to be checked/subbed. Look at my little diagram for the circuit layout. I had to do the same thing to my ctc16 a couple years ago. Basically, you need to check out that .1uf and that 47ohm. the .1 cap is a troublemaker and can be very leaky and cause your cathode current to go way over its limit.
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Old 01-20-2004, 09:46 PM
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Since you guys were talking about D VOM and A VOM meters, I just recently picked up this seco model HC8 cathode current meter. Its the best thing next to the scope! Basically, just remove the HO tube, plug in the appropriate socket, and plug the HO into it (its a socket in series with the tube) and you can measure cathode current right off the bat. No unsoldering leads etc etc. The meter gives current figures for all the different HO tubes. Very handy. It was given to me by my local service shop. I think all of use should have one of these!
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Old 01-20-2004, 09:49 PM
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heres a pic underneath my spare ctc16. that big orange drop there is the .1uf that WAS replaced. The original is that dark red/brown color. Let us know how it works out!
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Old 01-21-2004, 06:07 AM
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Doug, thanks a lot for your detailed tips.

Last night I found a 6.3v 250 ma fuse lamp and put it in the cathode fuse clip and left it there. I adjusted the horiz eff coil for minimum lamp brightness (I had to turn the slug several turns into the coil). Also adjusted the horiz. centering control. I let it run for several hours and the burning smell is mostly gone, it is now just a usual smell of hot tubes. Flyback case feels a lot cooler now too. I think the lamp also helps to reduce cathode current by acting as a resistor. A severe overload should blow the lamp.

I measured the horiz. output screen grid voltage, it is 135 v.
and the negative grid voltage is -53 volts which are exactly right according to the schematic. If the cap and resistor that you found are bad, would they cause these voltages to be off?

That cathode current meter is amazing...never saw such a thing!

Last edited by Chad Hauris; 01-21-2004 at 08:10 AM.
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Old 01-21-2004, 11:26 AM
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HI Chad,
That .1 to ground could still be causing some trouble. I cant honestly say if that .1 will cause voltage changes. If the lamp in the fuseholder is cooling the flyback down, Id start checking values of some resistors inline with that fuse. They probably went down in value.
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Last edited by drh4683; 01-21-2004 at 11:28 AM.
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Old 01-21-2004, 11:38 AM
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I think I'll just go ahead and replace the .1 cap when I can locate a new one, and measure that resistor.

It wasn't JUST the lamp that reduced the current, I did adjust the efficiency coil to reduce the current, I just figured that leaving the lamp in the circuit would give an added safety margin of current reduction. I modified the circuit by adding the fuseholder w/lamp between the cathode and ground...the stock circuit was just 6JE6 cathode directly to ground.
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Old 02-03-2004, 02:39 AM
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Quote:
Originally posted by drh4683
Since you guys were talking about D VOM and A VOM meters, I just recently picked up this seco model HC8 cathode current meter. Its the best thing next to the scope! Basically, just remove the HO tube, plug in the appropriate socket, and plug the HO into it (its a socket in series with the tube) and you can measure cathode current right off the bat. No unsoldering leads etc etc. The meter gives current figures for all the different HO tubes. Very handy. It was given to me by my local service shop. I think all of use should have one of these!

That reminds me, Doug. I'll have to stop by the local Radio Shack one of these days and get a new VOM (I left my Micronta digital, along with two tool boxes and more spare parts than you could shake a stick at [!], back at my former home [in the basement] before I moved). I've had to rebuild my toolbox since I moved here, still have some things to get before I can say I'm done with the job, but it's not going to be as bad as it has been.



That Seco cathode current meter is an interesting piece of test gear, which I'm sure made it a lot easier for TV techs in the '50s and '60s to measure the cathode current of the horizontal output tube in TVs of that era (beats the pants off physically breaking the cathode circuit or any of the other dodges techs used to use to measure HO cathode current, that's for sure--the only one more simple than that was to use an adapter under the HO tube, between the tube base and the socket). I never saw anything like it before now, and I worked with electronics as a hobby for over 30 years (now more into ham radio, old small broadcast receivers and computers since moving to my apartment in a small town four years ago, but I still like reading all the posts [and seeing the pics of your old sets] from you guys who are still collecting old TVs like I did in the '70s. It always brings back fond memories).

I'm glad I am a member of AK. You fellows--and the guys in the amateur radio club I belong to--are the greatest! Don't know why I waited so long to join AK, but no matter--it was well worth the wait. You can bet I'll be staying with AK for a while.


Kind regards,
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Old 02-04-2004, 09:08 PM
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Here is a Sencore tester that is along the same lines. Its been very helpful to me being I still have lots to learn.
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