Are the CTC5 HV supplies weak?
 

I have my CTC5 Chandler up and running, but it just seems to have a weak HV supply; if you turn up the contrast/brightness the picture exhibits classic blooming. The HV supply drops down to about 15KV when that happens, pulled the plate cap of the 6BK4, still acts exactly the same. I have a new 6CB5, 3A3, and 1V2 in there, have not changed the 6AU4 damper since I don't have one on hand at the moment. I've heard reports that the CTC5 just has a weaker HV supply than the previous and later chassis, is this really so? Everything else seems fine except for this.

Yes they are less robust than the 4s and supposedly the 7s (the 7 is the only chassis below 11 I don't currently own) definitely weaker than the 9s.

IIRC the 5s are supposed to run 18KV for HV.
One thing I have found that helps the HV in the CTC-5 is to add an HV reg adjustment pot... The CTC-7 uses the same regulator circuit as the CTC-5 except that the 7 replaces a single fixed resistor in the 5 with a pot and a resistor...I've updated 2 CTC-5s with the 7 style regulator pot and the results have been significant improvements in HV performance in both sets.

I had the same issue on my CTC5. I checked everything and determined that the supply did not push out enough HV to allow the shunt regulator to work effectively.

The solution I had was to substitute a solid state replacement for the 3A3 rectifier. After the replacemement my set maintained a solid 21kV.

Never investigated if it was because the filament supply of thge 3A3 was insufficient.

The 5 is a dog HV wise, it was a departure from previous chassis for cost reasons (RCA attempting to stop losing money on each one sold), but it’s shortcomings were quickly reversed with the 7’s and all chassis thereafter. This makes it sort of a ‘one model only’ oddity- all previous chassis had good HV, so did all the ones that came after. I suspect the lack of brightness caused by the weak supply led to customer complaints, which caused them to bump up anode voltage nearly to previous levels in ensuing models.

I’ve tried everything to get move voltage out of my Wingate- I added a HV pot for the shunt tube (didn’t help at all, in fact you can remove the 6BK4 completely and you probably won’t even notice), added a H-drive pot in an attempt to run the horizontal output tube harder (marginal improvement, but still saggy HV on bright scenes), and installed one of those solid state stick rectifiers. Despite all my efforts, I still cannot eclipse 21kv with an image on screen. I still haven’t done the contrast pot mod so that would help a bit, but the main issue is how the FBT is wound.

There is too much primary winding impedance in the coil, which according to ohms law places a hard limit on how much current can pass through it. Meaning that for a given B+ voltage, no matter how hard you drive it you’re only getting so much output from it. Since I cannot alter the primary resistance, the only other variable I’m left with is running more B+ voltage to the circuit to attempt to get more out of it. I may try a dedicated silicon rectifier instead of feeding it from the normal 5U4 tube rectifiers, but I suspect other modifications would be necessary since width tends to grow at the same time.

If I ever get time to do it, I’ll report back.

I went through the same process and wasted a lot of time. I had considered a fly back swap from a later color set.

Did you try the solid state 3A3 replacement? It plugs straight in and boosted the HV to where the 6BK4 actually shunted some current. It regulates now at 21kV better.

But look at the bright side: if the 6BK4 fails, at least you won't be bombarded by XRays!

Face it - the CTC-5 is built for prime time viewing only (after sunset). :D

That’s what I meant by stick rectifier, they have goofy non-tooby part numbers so I just call it stick rectifier like the focus rectifiers from later sets. Heck it may even be possible to couple the primary side pulse into the secondary with one of those huge doorknobs and another HV rectifier like they did with chassis like the 2B, but I still think giving the whole circuit a boost with a silicon rectifier feeding it makes more sense and is less complex than doing all of that. There’s also the donut unwind and a tripler module solution, but I don’t like the idea of flyback surgery unless absolutely necessary.

I dont think it applies here BUT I have noticed some newbies expect
room lighting brightness from old sets. That comes in the '70s !
People watched these sets in a darkened room. Making it bright only
brings on troubles & stresses Hoz / HV stages.

On solid state tubes they work but are very unreliable. For a while when
a set came in with arcing filament windings I cut them out.
On a lot of sets it was a PIA to change them. Put in a SS rectifier saved
time & I didnt like doing filaments anyways. But in less than a year they
all were coming back with bad rects. So much for being lazy !
BTW if you cut open a "stick" rectifier it is made up of a series stack of
little disc shaped diodes.

73 Zeno:smoke:
LFOD !

I have read that; I have seen the same. I am 74, so I just "Might" have been around when color was the new thing. EVERY store that sold early color sets had a special room in which the color sets were located. It had a door and the light was rather low in that room.

It is absolutely correct that our early color sets will not have the brightness of a Plasma set. I still have an RCA CTC-9C in queue. I have gotten a raster after rebuilding the power supply but have more to come. I replaced the CRT with a good used 21CYP22A and have a good bright raster.

Our age is close. I do remember the TV rooms & also audio rooms. At the shop
our sales floor was up front with big windows. The only sets you could really
watch were Zenith Chromacolors & Sony trinitrons. In about 1976 the
Zenith EFL CRT's came out. They could light a room for abt 80 watts !
Well things do change. For the 2 years Studebaker built the Avanti
it was the fastest production car in the world ( with factory Paxton supercharger ). Now tech has left that behind but I would rather have the
real & simple thing.

73 Zeno:smoke:
LFOD !

I think those stick rectifiers are selenium. You there might be high enough voltage diodes out there now where you can use a few. Maybe 3D print a holder for them…

I did something like that with 5KV diodes that mouser sells (IIRC the PN was something like RF5000) in my 21CT55. Six of those diodes in series potted in Silicone is about as good as a 3A3.

you mean these? :D

https://www.mouser.com/ProductDetail...gw1Kdkdg%3D%3D

but now they also have THIS!

https://www.mouser.com/ProductDetail...Tvzect5w%3D%3D

beefier, cost a bit more, but you need 2 or 3!

However, that big one seems very VERY slow, it seems this one is better rated for the horz freq over all!

https://www.mouser.com/ProductDetail...BtEumNKQ%3D%3D

Yeah, I know these old color sets just don't get bright, but what threw me off was the fact it acted like the HV was just not strong enough, and I ended up confirming it. The picture is bright enough to watch with some outside light coming in the room, so I'll just run with it and be happy I have a good AXP tube in my set.