Smoking Pot! - Videokarma.org TV - Video

TubeType · #1 01-14-2010, 01:02 PM

I had to pass this one along to the forum.
I came across this item on theBay and almost dropped over.
$247.16, so far, for a 5-megohm potentiometer.
The shaft will need to be extended to fit a CT-100.

Here's the link to:

RCA CT-100 FOCUS CONTROL??
http://cgi.ebay.com/ws/eBayISAPI.dll...m=130357843431

RDusel · #2 01-14-2010, 01:06 PM

Well that seller is certainly in for a windfall..
The high bidder has a feedback of 555 so they are not new to Ebay, I guess they know what the control is and how much it is worth.

Steve McVoy · #3 01-14-2010, 01:14 PM

Two fools is all it takes. If I remember correctly, you can buy 5 meg HV pots from Fair Radio or Surplus Sales of Nebraska for a few bucks.

TubeType · #4 01-14-2010, 01:48 PM

FYI ... you can dismantle the defective original and stuff it with a more modern 5-megohm pot.
Once reassembled, it looks just like the original.
Pete Deksnis has a photo of one of my stuffed pots at his CT-100 site.

http://home.att.net/~pldexnis/simpli...eory_menu.html

Regards,

jeyurkon · #5 01-14-2010, 02:22 PM

Well, this one has a crack in the back so they're only asking a "Buy it Now" price of $229.99.

http://cgi.ebay.com/VINTAGE-TV-TELEV...mZ320474752446

Joh

*zenithfan1* · #6 01-14-2010, 04:49 PM

Geez, these people must be smoking pot. I would never pay that for a control pot, no matter what it's for. Like the others have said, there are alternatives to fix it cheaply and correctly. Lots of dumb-asses on eBay.

wa2ise · #7 01-14-2010, 05:30 PM

Well, a focus pot will have a couple KV across it, so a plain vanilla pot might not hack it. But focus pots were used in even the latest model VGA CRT monitors, so something usable shouldn't be that hard to find.

TubeType · #8 01-14-2010, 10:36 PM

For the CT-100, Sams 252-11 lists a Clarostat A47-5MEG-S with an FS-3 shaft for a replacement.
That's a plain vanilla, 1/2 W, pot with a linear taper and a 3" flat shaft.

Ouch! My head hurts from too much thinking.

wiseguy · #9 01-15-2010, 05:25 AM

what is listed in the sam's will not work correctly, trust me i have had 2 ct-100's and now one stored away with a bad no Red crt..those controls arc, there is HV even on the shaft at most times, this same control is also used in other Brand Sets that use a 15GP22.. my avatar is my CT-100 running..(or the working one)

TubeType · #10 01-15-2010, 09:26 AM

Hello Terry,

You are correct! The Clarostat A47-5MEG-S can and usually does arc in its' original "out-of-the-box" configuration.
I disassemble the new A47 pot and use the resistive element and the wiper to stuff into the old pot housing.
Also, a lot of creativity is needed to tackle this project.
Nice avatar, too. I prefer a little more contrast. My avatar is from a photo of B8001876. I recently picked it up in SoCal.
I will be recapping the chassis and installing a good CRT, in the Spring.

Regards,

pallophotophone · #11 01-15-2010, 12:41 PM

O.K. for the Ney Sayers among yourselves !
When was the last time some of you probably paid too much for something that you needed/wanted ? I'm well aware that when new it probably cost no more than 10 dollars. Just try to find one in a parts distributor today!!

But if you had been going to hamfests for years and searching out this style of control for as long as I have been, without success, and an opportunity arose when you could purchase a NOS unit after just doing very well for yourself on ebay, I'll bet you'd spend the money too.
Sometimes the pendulum swings the other way- a few years ago I was GIVEN a NOS 15gp22, still under vacuum that is going into my CT-100.

I'm glad I won it and have no regrets as I know I will be installing an original part and consider that an important part of the restoration! And no I don't replaced old capacitors and resistors with NOS ones. But I do like to do things correctly.

I have tried the process of using a physically smaller unit and the kiss of death is the lead and metal spacing consideration, also removing the metal cover. The smaller unit never cuts the mustard, by my experience.
And yes I'm 100% aware of the need to isolate the unit from the chassis in all respects.

Don't be so quick to judge!!

Bob Hodge AKA "Pallophotophone"

Pete Deksnis · #12 01-15-2010, 01:26 PM

[1] Focus pots for the CT-100 are specified to be 2 watts.
[2] re the 30-meg pot on ebay as noted above: the focus pot is in a resistance divider; the pot on ebay will skew the divider by what, 30/5, six times

TubeType · #13 01-15-2010, 04:06 PM

Hi Pete,

In my situation, the .5W pot fits nicely into the original pot's housing and meets the maximum calculated power rating required.
The 4.5KV source for the focus voltage is developed across the 5Meg focus pot (R23) and an 8.2Meg resistor (R180).
The calculated power for R23 is .5W and R180 is 1W. It's standard practice to spec these components at 2X their calculated ratings.

Regards,

Pete Deksnis · #14 01-15-2010, 07:24 PM

Hi Terry and all,

The third thing I look for when searching for CT-100 focus pots is linear taper.

5-Meg, 2W, linear taper. Can be tough to find, but doable.

To review: focus pots are in demand because they are subject to overstress when the convergence transformer shorts. That's the real culprit; not the focus pot. Thanks to John Folsom who had a couple of runs of convergence transformers manufactured, focus pot failure rate is no longer the headache it once was. Install a new transformer, probably get a pass on your focus pot going cherry red.

Pete