Predicta Holiday restoration

[bandersen]

Originally Posted by Down Under

Great news!!

I regularly look for Tandems on ePay, and it's interesting to note that the CRT case seems to show in a range of shades on the various Predictas that show up. I can't tell if it's the white balance setting on the camera, or if the plastic goes darker over time.

I too have read about the flame retarding chemicals in plastic going browny yellow. Does anyone know if the green area at the front edge of the screen should be tan in colour? Mine is green and it looks OK.

Catchya,

Adam

I suspect it's the camera and lighting. All the Predicta CRT cases I've seen in person (including four Tandems) are pretty much the same color. You mean the border around the picture tube ? It's definitely greenish

[Down Under]

[QUOTE It's definitely greenish [/QUOTE]

Ah! That's exactly how mine looks. I like it actually, I think it looks better than a tan border would. I only hope when I get time to look at my Holiday, the tube has some life in it.
I LOVE your Tandem!

[bandersen]

I decided to give this veneer a try. It's real mahogany sliced very, very thin with a paper backer.

I've got about 10 feet on ebay for 12 bucks so plenty to experiment with. First I'll try a test with red mahogany stain.

[rrrhre2s]

I think I am posting about the right set.

Been thinking about your restoration in the...
Predicta "Holiday" restoration p13o?

http://www.youtube.com/watch?v=UlHtGky46r4

at about 16:05 the LED Back light was staying lit for quite a while.

I believe if you connect the high side (ungrounded) lead of the LED to the high side of the filament string it would stop the strange behavior.

My theory is that since LED lighting will stay lit with only 3.2v across them at
a very low current, the capacitor is holding enough charge to cause the LED to stay lit until the charge is depleted.

If you relocate the lead to the (top) of the filament string the resistance of the tubes will drain the charge at that point almost immediately, so the LED will extinguish almost immediately.

The voltage at this point is AC and there is no DC path back to the filter capacitors.

Have a good day...
Love your restoration videos...

rrrhre2s

[bandersen]

Thanks, yes, this is the same set. I'll give that a try next time I get it up on the workbench.

[Kamakiri]

Originally Posted by bandersen

I did some searching on the web and discovered Ametherm has a nice line of thermistors including these with a cold resistance of 220 ohms.

1 Amp max, 2.2 ohm hot
http://www.digikey.com/product-detai...873490?cur=USD

2 Amp max, 0.9 ohm hot
http://www.digikey.com/product-detai...873476?cur=USD

Been using this thread as a guide for quite a bit here, thanks for being so in depth on this Bob

Which one did you end up using? I'm assuming it replaces the circled part in the diagram.

Also, the disc cap that's just below that, in the Sams it lists it as C47, having a value of 82 @ 5 kV. I assume that's 82 PF?

[bandersen]

I used two of the 1 Amp max versions in series to best approximate the 400 ohm original.
The steady state resistance of these devices depend on the current through them. Running only 0.6A through the 2A version would result in a fairly high "hot" resistance.

Yes, 82pF. I left all the original ceramic caps in place.

[Kamakiri]

Just about ready to plug in the variac and give my Predicta a first go. The only thing I can't find nor figure out is.....while attaching the picture tube, there are two single long leads.....one of which goes to pin 2 on the picture tube, the other goes to pin 6.

I can't see where the heck they're supposed to plug into the chassis. Anyone know offhand?

[bandersen]

I believe pin 2 is the video which goes to a post on the main board. Pin 6 is focus which goes to either ground or boost - which ever gives better focus.

[Kamakiri]

Any idea of *where* on the board these go? I can't find any info on it anywhere.....and there are a lot of posts on the main board.....

[bandersen]

The one that doesn't have any wire wrapped around it.

[Kamakiri]

I believe that I found pin 6's connection to chassis, please confirm that I'm correct here:

http://antiqueradio.org/art/predicta16.jpg

Now, just have to figure out where the other wire goes. I swear that I noted this somewhere, but the set's been apart for two months now, and I can't find anything I might have written.

[bandersen]

I think you have the CRT pin numbering off a little. Pins 2&6 are connected internally to the focus element. Pin 7 is the cathode which connects to the video output.

Page 17 of the Sams Photofact shows how the wires connect to the main board. That's what they call "CircuiTrace Numbers". #20 goes to the cathode of the CRT (pin 7 not 6). That's what you have labelled as "CRT lead"

The last wire should end in a spade terminal. There are two possible places for it to connect on a little terminal strip in the center of the chassis. If all else fails, you can just leave it disconnected. The CRT may be a little out of focus but will work.

[Kamakiri]

I found the wire, finally. It came unsoldered from one of the chassis plugs.......d'oh.

[bandersen]

Now that the weather is FINALLY warmer, I started work on the cabinet.

I found the thermistor disc while cleaning out the cabinet. I wonder how many sets were retired because the disc fell out ?


The sides and front are in pretty good shape.


I figure they used a metal mesh bottom for ventilation.


I'll try to touch up all the nicks and dings.


Legs and bottom removed.
It may looks like real mahogany, but I'm pretty sure it's poplar painted red.


Fully disassembled cabinet. I made an attempt to touch up the large area of finish loss on top, but it looks terrible.


So off it comes. Much was scrapped off and liquid stripped used in the stubborn areas.


New paper veneer prepared. I coated both surfaces with TiteBond Wood Glue and allow to dry.

This particular glue can be reactivated with heat for seven days.


Not bad, but I might give it another try. This veneer is so thin that any defect, including variation in glue thickness, is telegraphed onto the surface. It's so thin that they can;t be sanded out.


Finally, after a little Brown Mahogany Mohawk toner. It's a little darker and redder than the original but not bad. If I were to do it again, I'd try Prefect Brown toner instead.