EICO 47A Signal Tracer

[Platefire]

Got a Amp Tech friend that has two EICO 47A signal tracers as shown on attached link. He was telling me for repairing amps, this is what I need and was willing to sell one or make a trade for it. I did a short e-bay survey and determined they must be worth $50 to $100 dollars. Is that about right or not and has anyone has experiance with one of these? Platefire

 http://www.radiomuseum.org/r/eico_signal_tracer_147a_147_a.html

[sluckey]

I've never heard of EICO 47A. Do you really mean EICO 147A? If so, I used one quite a bit while in tech school and working in a radio/tv shop during the '60s. It was helpful only a little bit for AM radio or audio troubleshooting.

You sure don't need one to work on tube guitar amps. Don't you always have another working amp sitting nearby? If so, just build a simple probe and use that as a signal tracer. All you need is a guitar cable, 0.1µF/600V cap, meter probe, and gator clip. Probably junk box stuff that you already own. Much better than that mosquito sounding EICO.

Gonna need a signal generator (or some other constant signal source) too.

[eleventeen]

If you are talking about "$50 to $100 dollars", allow me to make the following suggestions:

1: For well under $200 and maybe under $100, you can buy a nice, functioning oscilloscope which is about 31 times as useful. I see Tektronix 2215's (50 MHz a THOUSAND TIMES more than you need) all the time for $120. Look on your local Craigslist for "oscilloscope" or "Tektronix" and I guarantee you will find one, if not this week, next week. And by the way...the same guy who has the 'scope might have some other old electronic stuff lying around. The bandwidth you need to do audio is essentially zero. New import probes on ebay: $10-$12 each. Maybe they come along with the used scope you buy. That's a plus, but any such probes are probably going to be fairly worn and perhaps flaky. Doesn't have to be a Tek..... Leader, Hitachi, Kenwood, B&K all made scopes that are 3 generations obsolete by now and should be available practically for the asking, but are perfectly usable for audio work. Plug it in and see if it lights up and see if the trace is bright without having to turn the brightness control all the way up.

You might find a $20 old tube-type Heathkit scope at a garage sale but I would steer you away from such a thing unless it is in sparkling, pristine condition. Oh, and don't get your hopes up, those old scopes are full of 12AU7s and 6DJ8's with barely a 12AX7 in them. Those old scopes use crappy probes that don't have the hook-on aspects of newer probes, and they might need service themselves. I *will* say, they usually have about $10 worth of knobs on them.

2: If you really believe you need a signal tracer (which I consider a goofball piece of equipment in case it isn't clear), you can make one out of a powered computer speaker that you buy at a garage sale or thrift store for $1 or $2. You'll have to figure out a way/method of constructing a probe sort of item for the front end and you will have to include a 600 volt capacitor of practically any size .01 > .1 to protect the low-voltage solid state world inside the powered speaker from the HV world of tube amps.

And as Sluckey said, even with such a signal tracer, you still need some sort of oscillator (OK, I guess you could use a radio output or there are tone sources you can get online or you can record a CD of audio tone) to generate an audio signal) but the normal way is to have an audio gen at the front end of whatever you are troubleshooting. Hey! Look on CL for one of them, too.

Scope = massively superior. The comparison in terms of general utility is what I call "NEC": Not even close.

[sluckey]

Here's a simple home made probe. This one has a cap and a detector diode in it but all you need is the cap. Betcha can make one that looks as good in about 10 minutes. 

[Platefire]

I'm sorry, yes it is a 147A. So the 147A would have to have a signal generator? it wouldn't pickup a guitar signal or mic signal? I like the medicine bottle probe! I got the bottle, got the cap, guitar cord, ground clip, screw/probe, shrink rap and plenty of amps to plug into.

I had a Tektronix scope I got at a thrift shop that I worked on a while. I killed the best MM I ever had on the Tek, I guess I got on the super high voltage section. Even when I changed the fuse out in the MM it was loco from then on. I think the scope picture tube was lame itself. I finally gave up on the scope, gutted it for parts and threw it away. A good working scope would be great but no more amps than I work on and my technical ability, probably overkill.

Thanks, Platefire  

 

 

[HotBluePlates]

it wouldn't pickup a guitar signal or mic signal?

It will, but they're saying you can make your own probe (radio shack probe, coupling cap, guitar cord, gator clip) for very much less money and plug the probe into any working amp you have.

... So the 147A would have to have a signal generator?

Yes... the EICO would need some form of external signal applied to the amp under test to have a signal for it to pick up. For radio, this is generally easier because there's RF signals flying in the air.

[eleventeen]

Don't take that one experience with an evil scope as a permanent wave off. It's the proper tool for the task and usable for lots of other things. An old EICO signal tracer with a cruddy probe that doesn't clip on to things like modern probes do and a metal chassis and a 2-wire line cord is...Fred Flintstone. I guess some would call a Fender Tweed Bassman Fred Flintstone. The sig tracer is such a primitive tool. It is usable, I suppose, but really, don't spend money on one. $10, tops.

And as far as the audio source at the input....BOTH the scope and the sig tracer need one. Here is what you DON'T want to do: Have your probe in one hand, trying to lean it against whatever point in the circuit you are trying to trace, while your left hand is holding the neck of the guitar you are going to strum...you know, with the grounded strings and all...that fade after 2-3 seconds and NEVER emit a constant level...and your +350 volts is on the right....and....you get the picture. Don't go anywhere near that. Get the whole picture: You need an audio source and a way to trace it. A thrift store radio is a perfectly fine source of audio, just again, isolate the solid state world between it and tubeland with a 600 WV capacitor.

[Platefire]

I can certainly see where strumming on a guitar and trying to probe a live tube amp circuit could be hazardust to your health. 

regarding a radio audio source---I guess a CD player or radio, anything you could plug in the test amp input for a constant audio would work? 1/8" male headphone plug to 1/4" male plug to go in guitar input of test amp? Platefire

BTW-It seems with all the modern micro electronics/chips a scope should be available in something about the size of a calculator???

[eleventeen]

"BTW-It seems with all the modern micro electronics/chips a scope should be available in something about the size of a calculator???"

They are! They're called scopemeters and an assortment of them can be seen searching for that term on ebay. And...the ones that are 2 generations old are not that expensive.

Yup, any audio works or 'can' work for an "injection" signal. It's just that the way preamps handle square (sharp corners = lots of high harmonics) waves gives subtle clues to what might be going on...and of course, the radio signal is constantly changing and full of complex waveforms that are never of one frequency. A real test bench has real tools, if I can say that without sounding like I'm denigrating anybody or anything. Those tools are probably cheaper now than they have ever been; some of my reco for them is traditionalism, some is the idea that good-functioning test gear allows you to determine things with real certainty, quickly, and there is piece of psychology > confidence involved in taking the readings you suspect are right or wrong and testing your theory as to what is going on with a particular item. Some mechanics insist on Snap-On tools, some are content with Craftsman, and some are happy with cheapy imported stuff. And I'm not saying that a 15-year old scope is Snap-On or anything like that. Personally, I just really really hate taking "no" for an answer from electronic stuff, so I like being able to beat it into shape, which means I like to be able to drill down to the problem. If I can. If I *can't*, then that lets me know that there's something I don't understand so I should STOP and either get some more info/insight, or at least let my brain reset as to my approach. To do that with confidence and yes, a certain degree of brutality, I need my weapons. Plus...once you have had and used decent scopes and good meters, then not having them feels like you are trying to fix stuff with sticks or nails or sumthin'.

[eleventeen]

[jjasilli]

Don't disagree with any posts here, but Geez, there's nothing wrong with a signal tracer. Different name for a "listening amp" that Doug recommends on the Library pages.

I have an Eico 147A.  Got it pretty cheap on eBay some years ago.  Changed the test-pin input jacks (Red +Signal & Black Ground) to a 1/4" phono jack & an RCA jack.  Has some usefulness.  I like to hear what an amp is doing even while doing other tests.

A 'scope is good but has steep learning curve.  Worth it though.

To digress:  A vintage tube signal tracer can also be used as a mini guitar amp.  Sounds a bit like an Alamo, or other bargain basement amps of that era.  Could use mods for more preamp gain to be used as a guitar amp.  Someone posted such mods here years ago.

[Platefire]

Seeing the pix of the Textronix in previous post makes me realize several years ago seeing several of these at a thrift shop but I don't guess I knew what they were and passed them over. All the logic about using a signal generator to get a consistant signal as oppose to a radio or cd player makes perfect sense. Don't know if I will invest in a scope but I will start looking at them more objectively.

On the EICO 147A, after what I've learned here I wouldn't spend much on it. My friend told me I could borrow it a while and try it out. I may do that. May trade something for it if he's not to proud of it  

Honestly for right now I would be happy just building the medicine bottle probe as a starter that plugs into an amp. I can always keep my eye out for a good deal on a scope or signal tracer--no hurry. Platefire  

[eleventeen]

"On the EICO 147A, after what I've learned here I wouldn't spend much on it."

That's really all I wanted to opine/convey. It'd be worse if it was funky and you had to spend $20-$30 fixing it up, only to have a semi-primitive tool. I am not going to tell you to go rush out and buy a 2-man Tek scope from the late 50's, either. But as long as it makes a trace, the lowest of low-end scopes can work perfectly fine for audio/amp work and as much as test/repair work has migrated to board swapping over the past 25 years...it's even more so today, so there are plenty of cheap scopes (and unemployed techs) out there.

The other thing is, and I have found this to be very true: If you are out there looking for used test gear, and you find someone who is getting rid of their scope, it's incredibly likely that they will be getting rid of a whole lot of other stuff too. Like parts. Like half-completed projects. Like stuff HE has gathered but has to get rid of or hasn't done anything with for 5 years so it needs to go.

The other day I found a guy selling two old tube amps on Craigslist. One is a Bogen, very old, in metal cage. Big sucker, uses 807s. It was $40, which is about right. The other was a Risson twin-6550 head, for $100.  No tubes included w/either. The seller offered to throw in an old junker dual 6L6 Alamo amp chassis. I wanted neither very much, but I figured I was only overpaying a little just for the power and output trannies. As it turns out, since I am always tearing apart surplus test gear and the like, I have a distinct lack of output transformers. Turns out, this fellow was getting out of the amp build game, and he just gave me all his old stuff.....which included his output transformer collection! Including a genuine Fender Bassman OT (that's basically a $100 item) and 2 brand-new 5F6 clone-chassis (Not my style but readily salable for $50 or so each) and a brand new Marshall chassis (salable for $50) and an 18 watt chassis (prolly use it for something) and a JTM-45 power transformer, brand new. Plus a dozen other trannies of various flavors, some big, some small. So I figure I overpaid $20 for stuff I didn't especially want but I got about $400 worth of other stuff.