Rare Hallicrafters CTC4 clone resurrected from the dead.

[Electronic M]

Originally Posted by zenithfan1

Damn. Now I know that ANYTHING is possible. That set looks absolutely beautiful!! Omedetou! Hontou utsukushii da na!!!

Mark, if you've been into anime long enough you should know that anything is possible there, but when the impossible happens in the real world it is either really awesome or really disturbing.


It is fitting that halicrafters had a CTC-4 clone in their line as, if I'm not mistaken, the tuner RCA and most clones used was a licensed halicrafters design.

This makes me really want to start getting that glorious lolipop color on my CTC-4 to work right.

[old_coot88]

Originally Posted by Electronic M

Mark, if you've been into anime long enough you should know that anything is possible there, but when the impossible happens in the real world it is either really awesome or really disturbing.

"The difficult we do immediately.
The impossible takes a little longer."

U.S. Navy Seabees motto.

[stromberg6]

Hi Bob, I'm curious to know how you resolved the dropping resistor situation. I also would have inserted it between the 4.5 amp fuse and the rectifiers, but upon looking at the schematic for my 4, I see that it would not be the best place to put it. I too am having voltage drop trouble with the original rectifiers, and need to replace them with 1N4007's, or equiv. B+ is about 345-350, not the 380 specified in the RCA lit, and when I crank up the variac the improvement in the pic is notable.
Thanks!
Kevin G.

[ohohyodafarted]

Originally Posted by stromberg6

Hi Bob, I'm curious to know how you resolved the dropping resistor situation. I also would have inserted it between the 4.5 amp fuse and the rectifiers, but upon looking at the schematic for my 4, I see that it would not be the best place to put it. I too am having voltage drop trouble with the original rectifiers, and need to replace them with 1N4007's, or equiv. B+ is about 345-350, not the 380 specified in the RCA lit, and when I crank up the variac the improvement in the pic is notable.
Thanks!
Kevin G.

Kevin,

I will have to get back to you in a couple days. I am going to relocate the dropping resistor in the lead that connects the out going leg of one of the half wave diodes to the main filter caps. I will post a drawing with the placement and the value of the dropping resistor when it is finished. That said, replacing the inefficient sleniums will bring back your B+ to a much higher level. It will probably be too high like mine is now.

I have been nusring a very nasty case of the flu for 4 days now and I think I will be back up and around in another day or so. Watch for a future post.

[Sandy G]

Dah-Yum, Bob, take care, 'n' get better soon ! DON'T get out & Horse Around the 1st day you feel better...Take it easy a few more days & let it get good 'n' gone...

[KentTeffeteller]

Bob, This restoration of an interesting set which was made in small numbers if that was totally heroic. In my book should be one of the Top 5 early Roundie restorations of the year if not the decade. Beautiful job.

[ohohyodafarted]

Originally Posted by stromberg6

Hi Bob, I'm curious to know how you resolved the dropping resistor situation. I also would have inserted it between the 4.5 amp fuse and the rectifiers, but upon looking at the schematic for my 4, I see that it would not be the best place to put it. I too am having voltage drop trouble with the original rectifiers, and need to replace them with 1N4007's, or equiv. B+ is about 345-350, not the 380 specified in the RCA lit, and when I crank up the variac the improvement in the pic is notable.
Thanks!
Kevin G.

Sorry it took so long to get back to you Kevin. I have had the flu and a million things to do and I just got to figuring out the placement and value of the resistor needed.

This is what I have done. Using clip leads I inserted a 1K 50 watt wire wound pot into the power supply circuit. The best place to insert the droping resistor is on either one of the leads of the power supply choke. I chose this location because it is the best place to insert and have the droping resistror effect all of the various power supply voltages.

While adjusting the 1K 50W pot, I monitored the B+ supply voltage and when I reached 350V (the specification on the Sams schematic) I recorded the voltage across the pot and the current through the pot. I dropped 72 volts and had 440ma currrent. I calculated about 32 watts of heat energy will be generated. Then I disconnected the pot and measured the resistance. 150 ohms. I have ordered some Vishay 50W 150 Ohm Aluminum clad power resistors from Mouser. Mouser Part# 71-RH50-150 at $4.67 each. I will mount the resistor somewhere on the top of the chassis where the heat will be easily disipated.

If you want to go with the 380v B+ as specified in the RCA print, then these values are what you will need. 70 ohm 20 watt, gives me 380v B+ in my set. My set seems to be functioning about the same at either B+ voltage. I get a nice full bright raster at either 350v or 380v.

If you replace the original stack rectifiers with 1A 1000piv diodes I would guess you will need to drop a similar amount of B+ voltage to get the supply voltages back within specification. Good luck, and I will post the photos of the mod in a couple of weeks after the new resistors arrive and I install them, so you can see how I did it.

[miniman82]

I think I might try finding some NOS selenium stacks for my CTC-4 Director, that's the easiest way to fix this problem. Like Bob I've been running a power resistor in conjunction with the new rectifiers, but the heat it generates is objectionable.

[old_coot88]

Bob,
Out of curiosity, what is the voltage on the heaters? If it's signifigantly over 6.3vac nominal, you might want to try dropping the line voltage itself with a bucking xfmr. Just a thought.

[old_coot88]

Originally Posted by miniman82

I think I might try finding some NOS selenium stacks for my CTC-4 Director, that's the easiest way to fix this problem. Like Bob I've been running a power resistor in conjunction with the new rectifiers, but the heat it generates is objectionable.

If the replacement seleniums are gonna drop the same voltage (and hence wattage) as the power resistor, they would be dumping the same amount of heat, would they not? That's why i thought maybe the problem could be overly high line voltage (verifiable by measuring the heater voltage). IIRC, Phil Nelson had a similar issue with one of his vintage restorations.

[jeyurkon]

I agree with old_coot. You'll still have the heat problem.

I purchased a bunch of NOS seleniums. I didn't have much luck with them. They were o.k. for low power applications, but when trying to run them near their ratings they would heat up and start dropping too much.

There is a conditioning process similar to reforming electrolytics for them, but I haven't tried it.

This company still makes them, CEHCO, but it might be expensive.

Originally Posted by miniman82

I think I might try finding some NOS selenium stacks for my CTC-4 Director, that's the easiest way to fix this problem. Like Bob I've been running a power resistor in conjunction with the new rectifiers, but the heat it generates is objectionable.

[miniman82]

Originally Posted by old_coot88

If the replacement seleniums are gonna drop the same voltage (and hence wattage) as the power resistor, they would be dumping the same amount of heat, would they not?

But they dissipate the heat over a larger surface area, and there's no bracket to hold an extra large resistor. Plus, it appears stock. For example, I mounted my resistor on a bracket that interfers with the opening of the HV cage cover. With stock seleniums, I wouldn't have that problem.

[stromberg6]

Bob, Thanks for the info about the dropping resistors . I'll be pulling the chassis soon for some other work, and will build a temporary setup to check out both approaches, 350 volts, and 380 volts. My particular chassis seems to do better with the higher voltage, as applied by a variac, but I don't want to run the entire set like that, and chance a problem. I'll post results as I realize them. Glad you're feeling better!
Kevin

[Electronic M]

Originally Posted by miniman82

But they dissipate the heat over a larger surface area, and there's no bracket to hold an extra large resistor. Plus, it appears stock. For example, I mounted my resistor on a bracket that interfers with the opening of the HV cage cover. With stock seleniums, I wouldn't have that problem.

The doubler lytics and seleniums are original in my CTC-4, and run cool with proper B+ at a slightly reduced line voltage from what leaves the outlet,s so I'm going to leave them be for now.

[ohohyodafarted]

Just out of curiosity does anyone have any insite as to why RCA used selenium stacks in the CT100 thru CTC4 series instead of 5U4s?

Starting with the CTC5 and going forward, RCA switched to using 5U4s.

Data sheet for 5U4 indicates it will produce 225ma of dc current. I don't know what the ratings of the selenium stacks are, but my measurements indicate that a pair of 5U5s in parallel would be enough to supply the 440ma I measured in my CTC4. And further, the B+ fuse in the set is 450ma.

Here is a link to the technical data for an RCA 5U4. I must confess I'm not much good at interpriting these graphs.

http://www.mif.pg.gda.pl/homepages/f...49/5/5U4GB.pdf

Do you think this was an issue of reliability/pushing 5U4s to their upper limit, or cost in manufacturing considerations?