Sentinel radio already "Fixed"! Ugh!

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Sentinel radio already "Fixed"! Ugh!

Post by terrydec on Tue Mar 22, 2016 10:16 pm

Thinking that I was getting a good deal I bought a Sentinel Model 344 on eBay. This is a ‘6’tube AA5, which is odd. It looks really good except for a crack near the back on top. The listing said, “It hums”. No problem, right?

Then I opened it up. The set has been worked on by somebody else. I guess they tried to fix it and couldn't so they passed it on to me. Someone has shot-gunned the whole radio replacing every capacitor and resistor. The set looks butchered. And it hums. Of course the filter caps have been replaced, and it still hums. Whooppee! I did have a signal at one point, but it faded out. It looks like they hooked the B- to chassis ground. Ouch! Look out 35W4!

Oh well, first- check tubes, (and cut that danged wire from B- to chassis ground. Thanks isolation transformer.)
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Re: Sentinel radio already "Fixed"! Ugh!

Post by Wildcat445 on Wed Mar 23, 2016 12:06 am

Sounds like you have a project on your hands. Fixing a hack is a good feeling. Good luck.

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Re: Sentinel radio already "Fixed"! Ugh!

Post by terrydec on Wed Mar 23, 2016 12:14 am

I do have one advantage. I have the original Sam's Photofact folder for this model.

BTW- There is a teensy tiny note that says, "B- to chassis on model 344 only". Embarassed
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Re: Sentinel radio already "Fixed"! Ugh!

Post by Wildcat445 on Wed Mar 23, 2016 12:41 am

The schematic is in 1953 Beitmans, page 123. I did not find it in Rider's and I don't have the Sams folder. The B- note is interesting.

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Re: Sentinel radio already "Fixed"! Ugh!

Post by Wildcat445 on Wed Mar 23, 2016 12:51 am

I found something interesting in Beitmans on your radio.  Listed in the Beitman's drawing are models IU-344 and 344.  What IU-344 is, I'm not certain.  In any case, B- in Beitmans is definitely drawn with B- to one side of the power switch, in the typical AC-DC power supply.  There are three notes in the diagram, none of which pertain to B-.  For what that is worth.

I have this schematic printed. The procedures for posting pictures has changed. If it will help, and if I can figure out how, I will post the Beitman's schematic.

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Re: Sentinel radio already "Fixed"! Ugh!

Post by Bill Cahill on Wed Mar 23, 2016 7:52 am

I know the feeling. I bought a Silvertone bakelite radio with the candy cane dial on ebay before I went to go for surgery. Two weeks ago I opened it up to work on it. The seller said it didn't work.
He didn't say it had been worked on. I pulled the chassis, and, removed bottom. Oh, No! Somebody had shot gunned caps. There are two Japanese electrolytics connected in parallel with the original, and, most paper caps were replaced with old paper caps such as imp, big chief, and, etc... I put it back together.

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Re: Sentinel radio already "Fixed"! Ugh!

Post by terrydec on Wed Mar 23, 2016 12:54 pm

Wildcat445 wrote:I found something interesting in Beitmans on your radio.  Listed in the Beitman's drawing are models IU-344 and 344.  What IU-344 is, I'm not certain.  In any case, B- in Beitmans is definitely drawn with B- to one side of the power switch, in the typical AC-DC power supply.  There are three notes in the diagram, none of which pertain to B-.  For what that is worth.

I have this schematic printed.  The procedures for posting pictures has changed.  If it will help, and if I can figure out how, I will post the Beitman's schematic.

Thanks so much but I have the original Photofact folder, not a copy. I got it online for $4.80. It's really good with 4 pages including an under chassis photo, parts list, schematic and alignment instructions.
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Re: Sentinel radio already "Fixed"! Ugh!

Post by terrydec on Wed Mar 23, 2016 12:57 pm

Bill Cahill wrote:I know the feeling. I bought a Silvertone  bakelite radio with the candy cane dial on ebay  before I went to go for surgery. Two weeks ago I opened it up to work on it. The seller said it didn't work.
He didn't say it had been worked on. I pulled the chassis, and, removed bottom.  Oh, No!  Somebody had shot gunned caps. There are two Japanese electrolytics connected in parallel  with the original, and, most paper caps were replaced with old paper caps such as imp, big chief, and, etc... I put it back together.

Fortunately it does look good enough for display.
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Re: Sentinel radio already "Fixed"! Ugh!

Post by terrydec on Mon Mar 28, 2016 2:59 pm

Well, now I know why it was so cheap. I give up. Defeated! I've just spent 3 hours trying everything I could think of. I keep running into cold solder joints, wrong value parts, bad wiring, etc. And I'm still unclear about the B- wiring to the chassis.

So, I'll pull the tubes and put it on display. Like I said, at least it looks really good and makes a nice addition to my collection.
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Re: Sentinel radio already "Fixed"! Ugh!

Post by Wildcat445 on Tue Mar 29, 2016 2:29 am

I have never seen an AA5 (6) that was wired with B- to chassis.  I'm not saying it does not happen, just that I've never seen it.  What if you ran B- to one side of the power switch like is typically found, clean up the wiring per the schematic, (not a Sams) and see what happens. Do you still have the hum?  What have you got to lose?

I would still be willing to print and post the schematic I have from Beitman's if it would help.

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Re: Sentinel radio already "Fixed"! Ugh!

Post by terrydec on Tue Mar 29, 2016 12:25 pm

Like I said, there are just too many problems. And the Sams is excellent with a bottom view of the chassis, alignment info and everything. I tried to fix some of the bad solder joints and clean up the chassis. I got a crick in my neck sitting at the bench for 3 hours with nothing to show for it. I think maybe the person tried an alignment too. Yes, I have a RF generator but I don't think anymore time spent on this radio would prove to be productive.

Thanks for all the suggestions.
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Re: Sentinel radio already "Fixed"! Ugh!

Post by Doug Burskey on Tue Mar 29, 2016 8:40 pm

Oh yes they made AA5's or 6's with B- chassis. Also known as a "hot chassis". Depending witch way plug is inserted into the outlet the chassis can have 120vac on it that makes it a shock hazard. I always fit a polarized cord or plug to any of those I restore so neutral will be connected to the chassis.

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Re: Sentinel radio already "Fixed"! Ugh!

Post by Wildcat445 on Wed Mar 30, 2016 2:39 am

I guess it's time to fall on my sword. I misspoke. I'm sorry if my comment caused confusion. Embarassed

The radio posted by the OP is a 1953 model, give or take. He had a schematic by Sams which, apparently, shows the filter caps connected to chassis. I have a Beitman's schematic that shows this radio having a typical floating chassis power supply with B- to the power switch. Sitting looking at the Beitman's schematic, I did not give consideration to the hot chassis sets. I had not seen filter caps connected to chassis on a floating chassis power supply, I guess, was the point I was trying to make. A better case in point would be this. How can the same radio have two totally completely different power supplies? I was attempting to figure out where the difference was. The radio has a hum. The schematic I was looking at suggested the radio might have had its filter caps wired wrong. That has certainly happened before. That radio had other signs of work being done in a less than competent manner. The OP has decided to abandon the project, so any further investigation would be moot at this point.

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Re: Sentinel radio already "Fixed"! Ugh!

Post by terrydec on Wed Mar 30, 2016 12:11 pm

Just a comment. The radio has had all of the filter caps replaced, which I of course replaced again. All of the other caps have already been replaced as have many resisters, either with the wrong value or the wrong size. The voltages are all within tolerances and sometimes it does get a very weak signal, but only if I touch the antenna terminal. That means the oscillator is working. And it still has a hum. I would have to go in and start replacing every component again, which is not feasible and would cost much more than the set is worth. I can't see how the Beitman schematic would help more than the Sams schematic.

Someone just kept replacing stuff willy-nilly. Who knows why but it didn't work.

BTW- This is not my first dance.
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