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 Post subject: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Jul Fri 30, 2021 1:06 am 
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Location: Pewaukee, WI
So a few weeks ago I bought a partially recaped Capeheart CXC-13 which I believe to be the only surviving example in private hands.
http://earlytelevision.org/pdf/capehart ... _327-3.pdf

The previous owner did a partial recap (only the paper caps) and the set is producing a picture with sound and color. All the B+ voltages are reasonably close to what Sam's calls for, and there's no hum.
What's driving me nuts is the low HV issue the previous owner was fighting. I've checked all parts in the horizontal and HV and changed all suspect parts. The set should produce 25KV but struggles to produce 20KV with the CRT dark and the HV reg biased to complete cutoff. With a bright-ish raster HV sags as low as 10KV and about the best it will do with a watchably bright picture is 16KV (with sags below on bright scenes). The focus seems to track the sagging very well.
The only thing that seems wrong besides that is the 4.7k 1W R140 had drifted up to 6.8k and the new 2W I replaced it with gets boiling hot... Disconnecting that resistor gives maybe 300V more HV under load and maybe 1-2KV more unloaded. I tried substituting a CTC-4 yoke into the set (since the horizontal windings are the same according to Sam's) and the HV ran worse.

Thinking the HV winding might just be weak I tried using an NTE528 tripler (out of a Zenith CCII SS chassis I had) and driving it's input off of the plate of the H out tube and got the same results as I did with the fly back supplying the HV...
I'm at the point where I don't know what to do to make this set produce proper HV... Anyone have any ideas?


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 Post subject: Re: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Jul Fri 30, 2021 3:41 am 
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Location: Belrose, NSW, Australia
Any sign of heat in the flyback core or windings?
Have you set the hor lin for minimum plate (cathode) current in the hor OP tube? Does this adjustment have a well-defined dip?

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 Post subject: Re: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Jul Fri 30, 2021 2:21 pm 
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Location: Beaver Falls, PA. USA
Recheck everything in the damper and boost circuits, and compare the previous owner's work to the schematic; something may be hooked up wrong, or a wrong part value might have been installed. I saw your post on VK.

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 Post subject: Re: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Jul Sat 31, 2021 9:36 pm 
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irob2345 wrote:
Any sign of heat in the flyback core or windings?
Have you set the hor lin for minimum plate (cathode) current in the hor OP tube? Does this adjustment have a well-defined dip?

It runs cool and there is no sign of wax dripage. I have dipped the current. It's drawing a very LOW 140mA. The dip is not very sharp compared to a CTC-4 or 16. There's a solid 1-2 turns of the Lin coil where the current doesn't move the needle in the dip.

Tim Tress wrote:
Recheck everything in the damper and boost circuits, and compare the previous owner's work to the schematic; something may be hooked up wrong, or a wrong part value might have been installed. I saw your post on VK.


I've gone through the entire horizontal circuit(and fixed all the iffyt things), but I haven't checked all the loads on the boost supply...the boost is only 30V low so I have a hard time believing it's loaded down bad enough to affect HV. I'll check it anyway.


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 Post subject: Re: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Aug Sun 01, 2021 12:16 am 
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Location: Belrose, NSW, Australia
Hmmm, 140mA, eh?
I assume you tried the damper tube.
What happens if you short out the linearity coil?

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 Post subject: Re: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Aug Sun 01, 2021 3:49 pm 
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Joined: Jan Thu 03, 2013 2:06 am
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Did you check/ replace the resister in series with the filament on the HV rectifier?


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 Post subject: Re: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Aug Sun 01, 2021 4:14 pm 
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I'd say the low HOT cathode current is the problem. It's a balancing act between the flyback providing enough HV with no load and the regulator pulling the HV down to the correct voltage. If you increase the cathode current by adjusting the linearity coil, does the HV increase? I have seen sets where you are instructed to adjust the linearity coil away from the dip if the regulator current is too low. In this case, it's so low I don't think it's an adjustment problem, but it might give you some clues. Maybe you're so far from the correct tuning, than you're in the wrong dip.

That hot 4.7k resistor is another thing I would look at closely. Don't assume the schematic in the Sam's is accurate.

I would expect the flyback to overheat if it had shorted turns, or arc if there was an open turn.


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 Post subject: Re: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Aug Mon 02, 2021 6:42 am 
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Have you checked the HV rectifier? The filament resistor?


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 Post subject: Re: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Aug Tue 03, 2021 3:13 am 
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irob2345 wrote:
Hmmm, 140mA, eh?
I assume you tried the damper tube.
What happens if you short out the linearity coil?

Yes no change with a 6AU4 damper from a different working set.
There's a tiny reduction in HV shorting the Lin coil (varies depending on which 2/3 I short) and not really any change in cathode current.

Penthode wrote:
Have you checked the HV rectifier? The filament resistor?

It tests fine in my B&K 606. I double checked it and checked the resistor by replacing it with a solid state HV rect...HV performance is identical with tube or SS rect.
Image



ac wrote:
I'd say the low HOT cathode current is the problem. It's a balancing act between the flyback providing enough HV with no load and the regulator pulling the HV down to the correct voltage. If you increase the cathode current by adjusting the linearity coil, does the HV increase? I have seen sets where you are instructed to adjust the linearity coil away from the dip if the regulator current is too low. In this case, it's so low I don't think it's an adjustment problem, but it might give you some clues. Maybe you're so far from the correct tuning, than you're in the wrong dip.

That hot 4.7k resistor is another thing I would look at closely. Don't assume the schematic in the Sam's is accurate.

I would expect the flyback to overheat if it had shorted turns, or arc if there was an open turn.


It was dipped when I got it so I rotated it several turns in both directions and watched 2-5mA increase on the meter. I could try detuning it for more current, but I'm not fond of adjusting it more...the brass adjuster on top is the only adjustment point (bottom of the core has small a perfectly round hole, but nothing for a flat edge or hex tool to grab), and on top of being in the HV cage 1/2" away from 380V B+ fuses and damper and focus terminals on the flyback it's also a bit sticky...all I have to adjust it with is a LONG thin brass screwdriver and doing so is a nerve wracking.

I know Sam's isn't exactly always accurate, but I don't know where to get another schematic for this...


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 Post subject: Re: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Aug Tue 03, 2021 4:32 am 
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Location: Pewaukee, WI
I've noticed something interesting... centering lowers HV 2KV if set to center. It will gradually climb back up if adjusted to either end.
This may or may not be related to R140 being unhooked (since it lowers HV when connected).


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 Post subject: Re: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Aug Tue 03, 2021 2:47 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Beaver Falls, PA. USA
Have you checked the drive waveform? Also, scope the B+ lines and make sure that they are clean; stray horizontal pulses can cause some weird things.

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 Post subject: Re: 1956 Capeheart CXC-13 Color, low HV issues
PostPosted: Aug Tue 03, 2021 5:22 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 525
Location: Austin, TX
How is the screen voltage on the HOT?

It seems like the problem may be related to the centering control circuit. Are you sure the control is good with no open sections, or poor tacking? What about T9, T10, T7, and C12?


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