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  #1  
Old 07-16-2017, 06:39 PM
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Suitcase TV Fun

Today, I decided to take a shot at repairing/restoring a couple of suitcase style electrostatic sets that have sat in a dark corner of my display room for at least 20 years. They seem to be virtually identical, but likely will offer up a few surprises.

The first is a Sentinal 400-TV, which I slowly powered up on a variac... all tubes including the CRT seem to have heater glow... no smoke, slight hum and volume control scratch, but no HV or sound. It is only drawing about 95 watts, so perhaps one supply is down. The base cap is stuck on the CRT, so I am proceeding slowly and carefully and have not removed either chassis.



The second is an Airline, which is in somewhat better condition (no chassis rust) but has an unfortunate hole drilled above the tuner knob, (perhaps for fine tuning) and no light from the tuner tubes, but otherwise behaves the same as the Sentinal (no HV, no sound, no smoke, about 95 watts draw).



Looking forward to some good fun in the days (weeks, months?) ahead.

jr
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Old 07-16-2017, 09:25 PM
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Two of the best playing '40's 7 inchers ever made. They don't take up much space either. They look like nice examples. With a little ingenuity you might be able to repair the hole in the Airline front plate. Good luck!
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Old 07-17-2017, 07:19 AM
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Power supply caps and the hv caps probably, just the usual. Hope the 7jp4s are good then it's all worth it.
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Old 07-17-2017, 09:12 PM
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I always liked the wood cabinet version. I think it was a Silvertone brand but the same set as these.
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Old 07-18-2017, 09:40 AM
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Quote:
Originally Posted by compucat View Post
I always liked the wood cabinet version. I think it was a Silvertone brand but the same set as these.
That was actually a Sentinel model. It's a fairly scarce one.
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Old 07-18-2017, 10:09 AM
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Quote:
Originally Posted by decojoe67 View Post
That was actually a Sentinel model. It's a fairly scarce one.
I've got one. I need to finish the repairs on it for it's owner....I may offer to buy it off of them once the resto is done.
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Old 07-18-2017, 03:13 PM
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Initial examination rf/if/audio chassis

At first glance, both appeared to be relatively untouched. I really see no signs of repair on the Sentinal chassis.



The Airline chassis has had the two electrolytic caps behind the terminal strip replaced with a two section cap.



However, its IF stages have also been modified to allow the use of 6CB6s rather than 6AG5s, perhaps for higher gain. There is a tag taped inside the set for a service company in Corvallis Oregon, which was a fringe reception area for Portland and Eugene stations. Hope it was aligned after the mods....

jr
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Old 07-20-2017, 03:16 PM
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Initial examination sweep/display chassis

Not so original here... both have had a bit of repair work. Here is the Airline:





And the Sentinal:



Looks like some good fun ahead sorting out the repairs and modifications made on these sets.

jr
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Old 07-21-2017, 12:14 AM
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The cat is alive, Erwin!

Bypassed the voltage doubler input caps to get some B+ and checked out both sweep chassis. Both jugs seem to make light, and both sweeps appear to be running on the Airline sweep chassis, while only the horizontal sweep is running on the Sentinal.

Airline:



Sentinal:



All voltages are low, HV on either set is in the 2.5 to 2.8 KV range. Some audio was heard from the Sentinal rf/if/audio chassis.

Both sets show promise.

jr
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Old 07-21-2017, 11:47 AM
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Quote:
Originally Posted by compucat View Post
I always liked the wood cabinet version. I think it was a Silvertone brand but the same set as these.
The Silvertone set was made by Tele-Tone. Totally different!
The Sentinel was a lot better design!
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Old 07-21-2017, 04:28 PM
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Interesting... Anybody here know how many manufacturers made these vertical format suitcase sets?

A little progress... it was fairly obvious looking at the schematic that the lack of vertical deflection and inability to focus the Sentinal set could be related to an open HV divider chain. I almost jumped out of bed and went back out to the shop last night when I figured that out, but waited until this morning to find and replace a couple of 4.7 meg resisiors in the HV chain. Set now makes somewhat of a picture, and will get a full re-cap this weekend. I always prefer to start with a semi-working set, so I can judge progress, and catch errors that I might make.



jr
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Old 07-21-2017, 07:02 PM
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Quote:
Originally Posted by dieseljeep View Post
The Silvertone set was made by Tele-Tone. Totally different!
The Sentinel was a lot better design!
Silvertone, Tele-Tone, and Firestone all were the same basic sets, although no wooden tabletop versions. I have the Tele-Tone version and it isn't nearly as good a set as the Sentinel/Airline models. There's also the unique Raytheon-Belmont 7" suitcase sets, but I've actually never seen one restored and working. They had a strange tuner design.
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Old 07-29-2017, 12:40 AM
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Quick update

Finished up re-cap job on the Sentinal sweep/display chassis, including selenium rectifier replacment. Chassis looks "wide open" but there are some caps that are difficult to get to, horiz oscillator is crammed against the chassis edge, under a wiring bundle and terminal strip.



Now I have a fairly decent, fairly stable pix, with a little bit of horizontal "jitter", HV is now about 4.5 kV, which seems a bit low, but I really don't know what is correct for this set...anybody know what it should be?



Ordered a NOS 6Y6 for the HV oscillator, and am going through about 50 6SN7s to find the best for the set. Will scope out waveforms to attempt to locate the cause of the jitter tomorrow. Perhaps I should re-cap the Airline sweep/display chassis next, to compare behavior/waveforms.

jr
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Old 09-08-2017, 04:07 PM
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Nearly There

Re-capped the Airline sweep/display chassis and both rf/if/audio/video chassis, and replaced a few resistors that were way out of tolerance, and now have 2 complete suitcase TVs that make a picture and sound, although more work is needed on each.

The Airline exhibits some horizontal instability and some flagging, I am digging for some better 6SL7s for the sync circuit. The new 6Y6 did bring up the HV to almost 5 kv, which I guess is close enough to spec.



The Sentinal HV is only about 4.2 kv, so another 6Y6 has been ordered. Arcing also occurs periodically, so I will have to fix that before it gets its new 6Y6.



getting close,
jr
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Old 09-08-2017, 05:38 PM
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Nice!
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