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 Post subject: Eico 147 Sig. Tracer features Amazing Melting Transformer!
PostPosted: Feb Mon 28, 2011 10:34 pm 
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Joined: Jan Thu 11, 2007 2:23 am
Posts: 544
Location: Colorado Springs, CO
I just recently picked up a handy-dandy Eico 147 signal tracer, and recapped the whole thing after I powered it up and it made a pretty hellacious humming noise whenever the speaker was active. It doesn't hum anymore (even less when I ground the chassis, but the transformer occasionally sounds a bit like it's fizzing (like a can of soda sitting on a table), and has started to buzz itself. I'm thinking it's melting internally for some reason, but I don't know why. The outside starts to get a little sticky after a while and I can see where the lamination goo (glue?) has been leaking out for some time.

If I run it at about 90 VAC it still works and the humming/fizzing is minimal, but obviously I'd like for it to work properly. I haven't had a chance to test all the tubes to see if maybe they've got issues and are drawing too much current or something. I did notice that a few of the old wax-paper caps had actually melted some over time, and I've since replaced them all with orange drops rated at 630V. I did check the voltages around the rectifier and they were all perfectly normal, so I'm thinking either some element is drawing too much current, or the transformer is failing, which would be quite unfortunate as I really like this thing; it would be really handy when I get around to troubleshooting my SX-73.

Any help would be appreciated!

Thanks,
Dan


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 Post subject:
PostPosted: Feb Mon 28, 2011 11:00 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7399
Location: Minnesota
I have never had a transformer problem with these. Did you replace the filter caps? are they installed correctly? does the transformer get hot?

If the transformer is just humming you can tighten the screws.

Dave


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 Post subject:
PostPosted: Feb Mon 28, 2011 11:04 pm 
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Joined: Jan Thu 11, 2007 2:23 am
Posts: 544
Location: Colorado Springs, CO
Filter caps are installed correctly as far as I know, I replaced them one by one, and as I said I checked the voltages and they were all right. The transformer is actually riveted to the chassis so I can't tighten the screws anyway, and it's definitely getting abnormally warm and leaking "goo" when it gets hot.

I did pull a couple of the tubes, and noticed two things: first, there's something small rattling around the Eico-branded 6SQ7, and second, the 6K6 almost looks like it's plates have oxidized. I'm going to check these tubes with my tester tonight to see what's up, I'm really hoping they're the problem...

-Dan


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 Post subject:
PostPosted: Mar Tue 01, 2011 12:54 am 
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Joined: Aug Tue 28, 2007 6:44 pm
Posts: 454
Location: Tustin,CA
The rivits may indicate that it was factory-wired. I recently had an Eico 145A go through my hands and its pwr xfmr, the same P/N as your 147A, had suffered a meltdown. That meltdown was probably caused by a shorted-turn. It wasn't caused by the filter caps or an external component. This failure-mode may be common with that specific pwr xfmr..
Dave - WA6VVL


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 Post subject:
PostPosted: Mar Tue 01, 2011 2:01 am 
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Joined: Jan Thu 11, 2007 2:23 am
Posts: 544
Location: Colorado Springs, CO
Thanks for the info Dave. Unfortunately that means I'm now on the lookout for a difficult-to-find transformer :( . From what I can figure, it seems to have 225VCT, 24V, and 6.3V windings on the secondary. I'm guessing the HV is less than 100mA, the tube filaments I can figure out later. Anyone know where I might find one of these?

-Dan


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 Post subject:
PostPosted: Mar Tue 01, 2011 2:41 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2617
Location: Monterey California USA
Humid or just damp storage often does unsealed transformers in, without there being anything wrong with the tubes or components. I lost the transformers in half a dozen pieces of hi fi and test gear when I had a workshop off a damp garage. The equipment would be fine and operating normally, then all of a sudden the transformer would cook off and let out stinky smoke. The paper used around the windings absorbs moisture and I guess starts corrosion and overall insulation breakdown. After I moved to a place with a dry workshop, the regular transformer failures ceased.

The navy takes the bigger transformers out of mothballed ship equipment and cooks them in an oven thing for a specific period of time before returning them to service. Not very practical for a small power transformer in a piece of test gear though...

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 Post subject:
PostPosted: Mar Tue 01, 2011 4:05 am 
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Joined: Sep Sat 15, 2007 10:12 pm
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Location: Amarillo, TX 79102
Look for a sigtracer for parts. Place a WTB ad in the classifieds on this Forum. They're not rare, after all.

Gene

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 Post subject:
PostPosted: Mar Tue 01, 2011 4:44 am 
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Joined: Aug Tue 28, 2007 6:44 pm
Posts: 454
Location: Tustin,CA
Both the Eico 145A and 147A use the same xfmr. I'm sure you can find a "basket case" if you're patient. If you're not, the 147A's circuit is very forgiving and will do well with lower voltages, So, a similar xfmr with 2-7/8" mtg centers will work. The 147A, after all, is just an audio amp. The replacement xfmr s/b similar to 540 VCT @ 40 mA. with enough 6.3 Vac to handle the 147A's tube load.
Dave - WA6VVL


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 Post subject:
PostPosted: Mar Tue 01, 2011 5:36 am 
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Joined: Jan Thu 11, 2007 2:23 am
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Location: Colorado Springs, CO
Unfortunately, I have the model 147, NOT the 147A, and it looks like the 147 and 147A are somewhat different; 147A uses a 6AQ5 and a 12AXy, 147 has 6SJ7 and 6SQ7, etc. I doubt the transformers are interchangeable then, since they have different part numbers...

-Dan


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 Post subject:
PostPosted: Mar Tue 01, 2011 5:58 am 
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Joined: Aug Tue 28, 2007 6:44 pm
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Location: Tustin,CA
Sorry, I must be getting "old" and missed the 147 vs 147A. Actually, the two pwr xfmrs are very close. The 6.3 Vac fils in the 147 are 1.6A while the 147A is 1.35A - a 1.6W mismatch - not large enough to cause ME any "heartburn" IF I had a 147A pwr xfmr going into a 147...
I think you have some flexibility here.... But, it has to fit under the 1629 eye-tube.
Dave - WA6VVL


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 Post subject:
PostPosted: Mar Tue 01, 2011 9:05 am 
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Location: Portland OR, grid square CN-85
Parts units shouldn't be too hard to find -- http://cgi.ebay.com/EICO-Signal-Tracer- ... 500wt_1076

There's some dreamer with a "Buy-it-now" price of $100, :roll: but if you watch, I'm sure you can find one at a reasonable price, they're still out there !

Check at local hamfests if you ever get to any, I've seen them from time to time, $15 to $25 seems to be what they're selling for. . .

Tom

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 Post subject:
PostPosted: Mar Fri 04, 2011 7:13 pm 
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Joined: Jan Thu 11, 2007 2:23 am
Posts: 544
Location: Colorado Springs, CO
I'm thinking that's what I'll have to do, but then again it seems silly to replace a failing transformer with another one which is just as likely to fail in the future. I'm also looking into more clunky options, including buying two transformers: one for HT and filament voltage, and the other for the eye tube filament voltage. The only trick is fitting the two in that chassis...

-Dan


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 Post subject:
PostPosted: Mar Fri 04, 2011 8:11 pm 
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Location: Portland OR, grid square CN-85
Hi there Dan --

Yeah, chances are that a parts unit will solve the problem as far as the power tranny goes. . .

Personally, I don't see how the power transformer will fail, anything short of having an internal short due to the storage in a moist environment. Aside from that, they seem to be quite reliable. The unit I've got, all I did was replace the paper caps, the power filter cap checked out fine.

Converted the output connector to a BNC, and that was it ! It seems to work well after that. . .

Good luck !

Tom

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 Post subject:
PostPosted: Mar Fri 04, 2011 8:38 pm 
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Joined: Aug Tue 28, 2007 6:44 pm
Posts: 454
Location: Tustin,CA
Hello,
The pwr xfmr can fail with a shorted turn. All it takes is a little scuff on the enamel coating. And, since I don't believe those xfmrs are impregnated, the windings can "move" eventually shorting out a turn. The pwr xfmr in my 145A and 147A, both the same P/N, were built by two different Mfrs. The one in my 145A suffered a "meltdown". There was no collateral damage on the secondary side and the filter caps, etc., were OK. I removed the xfmr, powered the 145A with a Heath IP-32 supply, and there were no problems.. You can carefully disassemble the xfmr to find the problem (aka autopsy).
Dave - WA6VVL


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 Post subject:
PostPosted: Mar Sat 12, 2011 2:07 am 
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Joined: Jan Thu 11, 2007 2:23 am
Posts: 544
Location: Colorado Springs, CO
I did some measurements/math today, and here's the parameters I found for the transformer:
1.6A @ 6.3VAC (for 6SJ7, 6SQ7, 6K6, 6X5)
0.15A @ 12.6VAC (for 1629)
? mA @ 500VCT (B+ supply)

the 500V figure was a measurement. The AC side of the B+ actually went from 500V to 490V once everything warmed up, so I figured a transformer with at least 500V would be sufficient. No idea about current though, and I don't feel like desoldering leads to measure it at the moment. I'm thinking I'll just go for 100mA or so, any thoughts? I'm almost ready to post in the WANTED section...

-Dan


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 Post subject:
PostPosted: Mar Sat 12, 2011 2:21 am 
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Location: Tustin,CA
Your B+ sounds way too high... The difference between the 147 and 147A is basically octal vs 7-pin/9-pin min tubes. The measured B+ in the 147A at the 6X4/V3 cathode is 332 Vdc at nominal line. The input cap is only rated at 450 Vdc. On the other side of the 1K resistor, it measures 290 Vdc with 0.75 VP-P ripple-voltage. Even the 147 schematic only shows 320 Vdc on the 6X5/V5 cathode. Soooo, I would stick with an xfmr that will give you a nominal 320 Vdc at the input to the filter caps..
Dave - WA6VVL


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 Post subject:
PostPosted: Mar Sat 12, 2011 2:24 am 
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I'm with Dave here Dan, sounds like your transformer is putting out WAAAY too much juice !!!

IIRC, I measured mine when I was playing, and it was nowhere even close to being that hot. I think that on my VTVM, it read around 280-290 ??? Somewhere in that ballpark, under 300 for sure. . .

Good luck !!

Tom

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 Post subject:
PostPosted: Mar Sat 12, 2011 2:27 am 
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Location: Colorado Springs, CO
You're right - I was measuring ACROSS the CT winding, rather than between one side and ground, which gives me 280VAC at turn-on, which drops to about 270VAC after warm up. I don't know the voltage drop across rectifier tubes so I didn't really know how to work backwards mathematically.

-Dan


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 Post subject:
PostPosted: Mar Sat 12, 2011 3:39 am 
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Location: Tustin,CA
Hi Dan,
Use your measurements which is similar to 560 VCT, or 280 V from one side to the CT. The B+ current in the 147A from the 6X4 to the input filter cap was 39 mA. In truth, any xfmr that will meet the pwr reqmt's and will provide 275 - 325 Vdc at the output of the 6X5 will probably be OK. You'll never see the difference operationally...
Dave - WA6VVL


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 Post subject:
PostPosted: Mar Sat 12, 2011 3:50 am 
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Joined: Jan Thu 11, 2007 2:23 am
Posts: 544
Location: Colorado Springs, CO
Thanks for the information. What exactly is the voltage drop across the 6X5? I know this circuit works fine for a range of B+ voltages, since I could supply it with as little as 90VAC and it still worked fine. I'm just hoping to get a relative range of transformers I can use.

-Dan


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