Author Topic: Sprague T03 Tel-Ohmike  (Read 6075 times)

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Offline k7rmj

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Sprague T03 Tel-Ohmike
« on: December 10, 2016, 11:54:18 PM »
I bought a Sprague T03 from eBay and it arrived today. It seems to be in fair condition. The front panel is in great shape. The case is dirty but no scratches or dents. Just lots of dirt on the original crinkle-finish paint. The leather carry strap is in really bad shape but 50 year old untreated leather isn't very durable. So I opened it up and the insides look very good but it will need some work. New caps. I found a pair of 25 uF electrolytics and four 1 uF electgrolytics that need replacing. Also found a couple of .02 bypass caps that are the old wax coated caps that need replacing. I also found a 250 ohm, 5 watt resister that I am suspicious of just due to its age. It's not burnt or anything but being that old I just don't trust it. It only has a power supply tube and the magic eye tube and both can still be found for sale as NOS. Soon as I round up the replacement caps and resistor, I'll give her the smoke test. Wish I had a variac transformer. I'll let you know how it goes.

Offline RJ

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Re: Sprague T03 Tel-Ohmike
« Reply #1 on: December 11, 2016, 08:08:18 AM »
Sounds like a plan. Post up some pic when you fire that puppy up!

Offline k7rmj

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Re: Sprague T03 Tel-Ohmike
« Reply #2 on: December 15, 2016, 04:27:47 PM »
It may be a few weeks before I work on that Sprague TO3. Good old PayPal strikes again.

I moved from the St Louis area down here to Hot Springs Village, AR in January 2016. Right after the move I went through all my accounts at various web sites and updated my address, shipping info, credit cards, etc.

Well, guess what? PayPal got my address change and entered it into their data base but that didn't stop them from giving out my old shipping address when I ordered some parts over the weekend. When I contacted them I was told that they have my current address for shipping and billing and it matches the credit card I have attached to that PayPal account and they are correct. The web site shows my current address for shipping to be here in Arkansas.

So I showed them a shipping receipt I got back from Parts Express where they sent my parts order to the address given them by PayPal... it was the old address. So, now I am waiting for them to wade through all the administrivia to get their mistake resolved and it may take a while before the Parts Express company receives their shipment back from the old address.

Sorry for the long winded whine but I wanted to let everyone know that this can happen. The PayPal representative I spoke with over the phone this morning said somehow that address was pulled from a historical file from old purchases made last year. She went through and purged their system of all my old shipping records to clear it up... I hope. She was very nice about it and wanted to help.

Anyway, life is still good here in Arkansas. I love living here in the woods. It's like being on vacation all the time.

Regards and 73  de Frank  K7RMJ

Offline k7rmj

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Re: Sprague T03 Tel-Ohmike
« Reply #3 on: January 26, 2017, 04:00:32 PM »
Greetin's all. I finally got everything worked out on the missing parts order so I placed another order this afternoon. This time I went with Mouser Electronics for two reasons.

The first reason is that they offered me a job back in 2002 as their Service Manager. I didn't take the job because a better offer came in the same day from another company LOL. It sure would have made getting parts easier and I love their location in Texas, but the other offer was just too good to pass up.

The second reason is that I could get all the parts and materials I need from them for the same price I would pay going with multiple vendors but only have to pay one shipping charge.

I am still not happy with my previous order due to PayPal's mistake in shipping. What a mess that turned out to be. Anyway, end of rant LOL.

I'll post more on the Tel-Omike when the parts get here and I can work on it again.

73 DE K7RMJ   Frank

Offline k7rmj

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Re: Sprague T03 Tel-Ohmike
« Reply #4 on: January 30, 2017, 12:31:07 PM »
Greetings all,

Well, I have good news and bad news. The good news is that the parts for my Sprague TEL-OHMIKE TO-3 arrived. I ordered them from Mouser Electronics. I ordered them on Thursday and they arrived on Friday, the next day and that was UPS ground shipping from TX. Kudos to Mouser.

The bad news is that I blew up one of the new filter capacitors.

Here is what happened. I replaced all the electrolytic caps. Then gave the two potentiometers a shot of control cleaner because they were rather old and looked like they needed it. Next I did resistance tests with my trusty VOM and all looked good. So I turned the chassis upright and sat it on the bench and plugged it in. That was mistake #2. Mistake #1 was that I did not give it good enough of a visual inspection, but I'll come back to that in a minute.

I don't have a variac to bring the AC up slowly and just couldn't wait so I plugged it in and turned it on. Everything good so far. No odd noises and no smoke... yet. So I sat back in my chair to let it warm up a bit and noticed the magic-eye tube came to life as everything warmed up and started working. So far so good. I turned one of the knobs and suddenly I heard a loud BANG and a loud hissing noise. WOW! I almost jumped out the shop window. And the smoke was just pouring out from under the chassis. So I yanked the AC power cord our of the outlet and stood there with my mouth hanging open wondering what had happened.

There was a LOT of smoke. It literally filled the shop so I opened the door and window then turned on the fan to vent it outside.

When I went back to the bench and turned the chassis upside down to find the problem, all the parts were there in place and none of the caps, new or old, had blown apart. So I started checking them closer and found that one of the new filter caps was extremely hot to the touch. On closer inspection I could see a small hole in the cap. It was about an eighth of an inch in diameter and there was a lot of yellowish brown liquid around the chassis under that cap. It almost looked like motor oil.

I thought I was being very thorough with this repair and had made sure all the screws and nuts and bolts were tight and had star washers where needed to get good connections to ground. So I poked around looking at all the solder connections with a magnifying glass and that is when I spotted the problem. There was a large solder glob puddled between one of the old solder connections and the chassis under one of the solder lugs. It was an old solder connection. Evidently this unit had been worked on before but it was a LONG time ago.

There was a layer of dust on the solder blob and it was not actually soldered to the chassis. Evidently when I turned the chassis back over to power it up this blob moved just a tiny bit but it was enough to short the circuit to the chassis ground. and when it did, POW. Instant smoke bomb.

After I removed the blob I made a series of tests again with the VOM and everything but that blown cap looked good and tested okay. I was really worried about the transformer because there was so much smoke but it tested good so I am hoping it didn't blow out. There were no charred marks on the transformer and no discoloration on the windings so I think it is still good. Those old iron transformers are tough to find and very expensive.

So, lesson learned. Next time I will check every single solder connection visually because you never know if someone else had already been inside and left a time bomb waiting to scare the bejesus out of you LOL.

Now I need to find another 30 MFd 450 volt capacitor. I think I will replace both of them. There are two in the power supply filter. But, with the minimum $6.95 whipping charge I think I'll wait until I get a larger order together before I order a replacement.

I'll let you know if or when I continue to try repairing this unit. It looks pretty good and cleaned up real nice when I gave it a bath but I am a little gun shy on this one.

I found more evidence that someone else had been inside it. There were two places where caps  had been installed in parallel to get the right values, and they did rather sloppy work. They went by that old rule for soldering, "The bigger the blob the better the soldering job".

73 DE K7RMJ  Frank