I've been wanting a porthole set for years, I always figured I'd find a Zenith first, but I picked up this Airline instead. It's a cool looking set, trapezoid shaped, wider on the bottom than the top. It's a 7" electrostatic set that uses 2 separate chassis, the bottom one has the power supply, tuner, IF, video, sound - the one on the side vertical, horizontal, HV. I'm not yet sure what that button on the front labeled "telephoto control" does. The cabinet really needs cleaning, what works good on these vinyl covered cabinets? pictures below...

Murphy's Oil Soap ? I think the "Telephoto" button is kinda like a "Zoom" control-it magnifies the image displayed by 1.5X or somesuch.

Cool set Adam, it's a rebadged Sentinel except the Sentinel isn't a Porthole and doesn't have the Telephoto button.

It'd be interesting to see the circuit for that button when you get a schematic.

Second the Murphys Oil Soap.

I think I have the schematic for this if you need it.

Here's the schematic at that zoom switch, it calls it an "expander switch".

I'm thinking that the switch allows you to make a small rectangular picture (with blanks top and bottom) or to fill the round screen and lose some of the picture at the edges.

There's some surface rust ontop of one of the chassis. What's worked for cleaning rust off chassis? I don't want to use steel wool, because I can see little metal bits getting in everything. I also don't want to use really rough sandpaper or a wirebrush that would put really visible scratches in the chassis. Maybe a little wet sandpaper 240 grit or so? Or what else works?

I might just sand and paint those rusty tube shields, and repaint the power transformer, but I'd rather not paint the chassis itself.

I'd try Naval Jelly before you break out the abrasives. Give it enough time to work -- at least half an hour. Clean up with wet paper towels.

You may still have some discoloration, but it usually improves things. By coincidence, I'm using this on a rusty chassis right now (well, this week -- I'm slow and lazy).

You can follow up that treatment with metal polish, if you're the polishing type. I usually don't bother for TV chassis. Too many projects, too little time.

Phil

I'm just looking to get the rust off and clean it a bit, not really shine it up. I'll try that naval jelly first, and pick up some of that oil soap at the store at the same time.

I just went and shotgunned all the paper caps and electrolytics in this set. There was lots of really messy repair work on this one, and I just wanted a neater looking chassis where I could see what went where before I tried it out. There were some caps that were replaced long ago, with leads of the old caps just left hanging there going nowhere, or new leads that were just tacked into position. Also someone just went crazy with the corona dope, covering many leads and solder joints with big gobs of it.

I'm going to clean the chassis, test the tubes, and do a little more poking around before I fire it up. Luckily, there's no rust on the other chassis, or on the bottom of the one, and also the wires going to the speaker in that pic are the only rotted rubber wire in the set, mostly this set uses cloth, and the other rubber is in good condition.

That oil soap is working good, you can really see the difference.

Messed around with this tonight, made some progress, have horiz and vertical, but no picture or sound yet.

Problem was a bad oscillator tube, works now, but could really use some vertical retrace blanking.

Hey, that reminds me about this thread: http://www.videokarma.org/showthread.php?t=247230

I was just about to slide a VT71 chassis back into it's cabinet. No time like tonight to try that circuit out!

I used that circuit on my 2 VT71s and it worked for me, haven't been able to figure anything out yet for this set though.

This 1st pic shows what I did to remove the retrace lines. 2nd pic shows the blanking pluses going into the crt grid. Any thoughts, possible improvements to my modifications?

That's a beautiful picture on that set! Now I want to break out the 7VT5A Motorola and do that mod, great work!

7" Sentinels rarely get their due performance wise. The Admiral usually gets credit for being the best performing set or best built or similar sentiment. I have one and they are nice, but the best picture I've ever seen in person on an electrostatic set was a Sentinel trapezoid.

After running the set for a while, the horiz was shifted over a bit to the right with the horiz blanking bar right down the middle of the screen. I thought first, I have no problems with horiz size, and 2nd in order to have the picture visible like that the horiz oscillator also has to be at the right frequency, and because there was no trouble with the vertical, I figured the problem had to be in one of the few components coupling the sync separator to the grid of the horiz osc.

But I replaced them all, and it made no difference! Then I just swapped the 6SN7s from the horiz to the vert, and it fixed it. I originally had put the strongest testing 6SN7 I had in the horiz, but the horiz osc circuits in these sets just seem to be really picky about tubes. Remember in one of my Motorolas, the horiz wouldn't sync, and the trouble was a tube, which also didn't work as the horiz osc, but tested good and worked in other circuits.

A tube tester may tell you nothing about how a tube will work as an oscillator. I have tried as many as half a dozen "strong" tubes before finding one that worked in a particular TV.

Phil

Any thoughts on what to use to patch up the speaker?

Cheapskates use tea bag paper and flexible fabric glue or some such. You can buy special "service cement" for this purpose; I have used it and I'm not sure it really works any better.

Purists may recoil in horror and advise different methods, but just between you and me -- that's a pretty low-fi speaker and it's going to sound about the same no matter how you repair it.

Phil Nelson

a patch made from brown bag paper and some white glue. But stay away from the edges. Honestly I dont think I would bother, I doubt you could hear it. The thing you want to avoid at all cost is getting any glue on the flexable edge.

That picture didn't really show how bad it is, it is something you can hear. I was already thinking of going the paper and glue route, just wondering what kinds of paper have worked better than others.

I have always repaired paper cone drivers with toilet tissue/tissue paper and clear nail polish. The nail polish gets into both pieces of paper, which sets up pretty nice. First you slightly wet the driver paper, then apply the tissue, then put another thin coat over the tissue and let it set. This method won't work well on the surround though, it's not flexible enough.

I have always had good results with rubber cement on flexible parts. Aileen's tacky glue works well on rigid areas and dries clear. Have you thought of re-coning the speaker?

Go with a flexible glue. Tea bag paper as Phil suggests, or something like it should work. Is there a tear on the opposite side that was previously repaired? There seems to be some lines in the photo that look like they may have been a tear.

You can always get it re-coned if you aren't successful. I'm really happy with the sound from one that I had re-coned.

John

I used part of another speaker, it doesn't look that pretty, but it sounds ok.

I used part of another speaker, it doesn't look that pretty, but it sounds ok.

Nice! :thmbsp:

You can also re-cone a speaker yourself if the spider is still intact. The kits are readily available online. I haven't done it myself but I have replaced surrounds with good results.

John

Finally got this one mostly back together. The naval jelly cleaned the rust off the chassis for the most part. I still have to put the crt socket completely back together (it was stuffed full of dead spiders), and I'm having problems with the contrast control, so I have to pull the bottom chassis out again. I picked up one of the knobs I was missing last month at that Lansing radio swap meet, but I still need the other.