CTC-4 Director 21

[old_coot88]

Originally Posted by SwizzyMan

Cant tell if this is a HOT cathode current meter or what. I dont think it is since the meter only has a range of 10 MA...

That meter is one milliamp full-scale. So it's probably wired to measure the HV regulator current. If it's measuring H.out cathode current, it'll have a low value shunt across it.

...and normal HOT cathode current is at least 100MA.

Normal H.out cathode is closer to 200 ma.

[SwizzyMan]

I wonder if the CTC-4 has those pesky HV issues like the CTC-5 does? I really hated dealing with that in my 5. And how is its performance? Hopefully better than my 5 too.

[miniman82]

5 is the only one with weak HV, you won't have any trouble getting a full 24/25 KV out of this set.

[SwizzyMan]

I was doing another current monitoring power up to keep an eye on the possible arcing area from crt to yoke shroud/housing. I discovered something very interesting and possibly damning. There is a strange orange almost neon-like discharge between the very edge of the internal coating to the shadow mask assembly im assuming in the crt. Now I dont suspect this to be oxygen molecules since the color of the discharge is orange not purple, but could this mean my CRT is in trouble? I don't think the tube is gassy since I can still get a nice, bright and full raster on the screen. I've noticed the glow kind of likes to jump around like some neon bulbs do (like electricity in a decorative neon flame bulb trying to find the path of least resistance). This is concerning me since I have never EVER seen anything like this. Your thoughts?

[ohohyodafarted]

Contrats! Appears to be a rather nice set condition wise. Although, I feel it's shameful that it has been butchered with an all glass tube. Just my personal opinion; as I feel that the real reason to own an early color set is to have the original rare metal crt and be able to see what an actual color picture looked like back in the day with a 21AX.

BTW: if you should decide to convert this back to the correct 21AX crt, I have a purity ring and the plastic insulation shroud from a ctc4 I would be willing to sell.

[bigaudioal]

Originally Posted by miniman82

5 is the only one with weak HV, you won't have any trouble getting a full 24/25 KV out of this set.

When working with my CTC-5 last week I noticed that all the service literature I have says between 19.5 - 22.5kV at the CRT anode. My CTC-5 is putting out exactly 20kV.

Why do I constantly see folks complaining about the CTC-5 not putting out 25kV when all the original service literature says lower than 25kV for this set is normal?

SAMS for early CTC-5 says 22.5kV
RCA Original Service Manual says 19.5kV
RCA Original Setup Manual says 20kV
SAMS for late CTC-5 says 22kV

See attached snip-its from some of that literature.

Just wondering as I have limited experience with vintage color sets.

Thanks.

[miniman82]

Originally Posted by bigaudioal

When working with my CTC-5 last week I noticed that all the service literature I have says between 19.5 - 22.5kV at the CRT anode. My CTC-5 is putting out exactly 20kV.

The problem is not the literature for the chassis, it's the specification itself. Not only did they choose an anode supply for the 5 chassis which only provides around 20kv to the CRT, they also for some unknown reason decided to not make up for that lack of voltage by having ample current reserves. To understand why this is a detriment, see note 3 of this PDF on the 21AXP22:

https://frank.pocnet.net/sheets/137/2/21AXP22.pdf )

I say lack of voltage because the 5 is the only one that low, all other chassis (especially the earlier ones) made a full 25kv and had more than enough current in the anode supply to make a full and bright picture without trying very hard. Add this to the fact that the data sheet on the CRT even tells the engineers that less anode voltage equals less brightness, and it will always be a mystery to me why RCA chose in this one particular chassis to do what they did. I don't care to speculate why it happened, it's an issue and makes the 5 a real dog in the brightness department compared to other sets.

[Electronic M]

Originally Posted by miniman82

The problem is not the literature for the chassis, it's the specification itself. Not only did they choose an anode supply for the 5 chassis which only provides around 20kv to the CRT, they also for some unknown reason decided to not make up for that lack of voltage by having ample current reserves. To understand why this is a detriment, see note 3 of this PDF on the 21AXP22:

https://frank.pocnet.net/sheets/137/2/21AXP22.pdf )

I say lack of voltage because the 5 is the only one that low, all other chassis (especially the earlier ones) made a full 25kv and had more than enough current in the anode supply to make a full and bright picture without trying very hard. Add this to the fact that the data sheet on the CRT even tells the engineers that less anode voltage equals less brightness, and it will always be a mystery to me why RCA chose in this one particular chassis to do what they did. I don't care to speculate why it happened, it's an issue and makes the 5 a real dog in the brightness department compared to other sets.

Add to that the fact that some chassis versions have a bass-ackwards brightness/contrast control circuit that has lots of interaction between controls, and some users were literally sending working sets to the repair shop because they could not manage to set the controls for a good watchable picture.

The 5s are the BOTB RCA color chassis in my book. If I had a nice 5 with a good 21AXP as well as my beat up 4 with a bad AXP I'd consider the 4 more worthy of the rare AXP.

[bigaudioal]

Originally Posted by Electronic M

Add to that the fact that some chassis versions have a bass-ackwards brightness/contrast control circuit that has lots of interaction between controls, and some users were literally sending working sets to the repair shop because they could not manage to set the controls for a good watchable picture.

The 5s are the BOTB RCA color chassis in my book. If I had a nice 5 with a good 21AXP as well as my beat up 4 with a bad AXP I'd consider the 4 more worthy of the rare AXP.

I have noticed blooming and focus issues while adjusting both the brightness and contrast controls.

[bigaudioal]

Originally Posted by miniman82

The problem is not the literature for the chassis, it's the specification itself. Not only did they choose an anode supply for the 5 chassis which only provides around 20kv to the CRT, they also for some unknown reason decided to not make up for that lack of voltage by having ample current reserves. To understand why this is a detriment, see note 3 of this PDF on the 21AXP22:

https://frank.pocnet.net/sheets/137/2/21AXP22.pdf )

I say lack of voltage because the 5 is the only one that low, all other chassis (especially the earlier ones) made a full 25kv and had more than enough current in the anode supply to make a full and bright picture without trying very hard. Add this to the fact that the data sheet on the CRT even tells the engineers that less anode voltage equals less brightness, and it will always be a mystery to me why RCA chose in this one particular chassis to do what they did. I don't care to speculate why it happened, it's an issue and makes the 5 a real dog in the brightness department compared to other sets.

Ah, I see. So it was the design of the set which produces the lower HV, thus being the least adequate to run the AXP. So the set literature is accurate and the 20kV is "normal" for a CTC-5. But that is barely enough to produce a decent picture compared to other sets of the same time period which produced around 25kV.

Very strange they did that considering the specs and notes on the CRT they were using.

[miniman82]

Originally Posted by bigaudioal

Very strange they did that considering the specs and notes on the CRT they were using.

That's why it's the runt of the litter, so to speak. For the same reason I, like Tom said, would cannibalize a 5 to get a CRT for a more deserving set. Done it many times. About the only ones that don't fall into that category for me are the more rare Deluxe doored models like yours, my Wingate and maybe a few others. But apart from that, they fall into the category of donors.