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 Post subject: Sweep Generator Woes
PostPosted: May Fri 21, 2004 2:04 am 
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Location: PA, USA
I’m having trouble getting my Eico 369 sweep generator to produce the correct waveform on my scope. After building a simple, broadband detector circuit (illustrated in the manual for the Eico 368), I connected it between the RF output of the sweeper and the vertical input of my scope, as shown in the manual. With the sweep width set to 0, I get a nice rectangular pattern on the scope, also as shown in the manual. <P>But when I increase the sweep width, no matter where I set it, I can’t get the ends of the top trace to slope down to the bottom “zero reference” line at all; they just end abruptly. In addition, the upper frequency side of the trace slopes down farther than the lower frequency side, no matter what I do. <P>I’ve also tried hooking up the sweeper and scope to an FM Pilotuner, as illustrated in the Sams Photofact for that model. And here too, the traces I’m getting look nothing like those illustrated. <P>Help!


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 Post subject: Sweep Generator Woes
PostPosted: May Fri 21, 2004 2:24 am 
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Location: Warwick,RI
I seem to recall reading somewhere that Eico had a major problem with one of their sweep generators.<BR>Don't know which one it was.<BR>Can anybody confirm this?<BR>Malcolm<P>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Fri 21, 2004 5:36 am 
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Location: Pocasset, Cape Cod, MA
If there's no tuned circuit ahead of the detector, the output would always be at the same level, wouldn't it? So you'd get a straight line, which is what you have? Sounds normal.<P>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Fri 21, 2004 5:44 am 
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Location: Burbank, CA and Thailand
I have a 369 that I bought, but haven't looked at or fired up yet. If you are unable to resolve the problem in a couple of days, I'll see if I can get mine going and maybe help you in the process.<P>Have you recapped it and/or done any sort of inspection or check out yet? I've bought a number of pieces of "vintage" test gear over the past year - some looked awful on arrival and some looked new, but I don't think any of them worked properly right off the bat.<P>I don't have a manual. Did you find yours online?<P>I'll follow the thread and see how you make out, good luck!<P>------------------


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 Post subject: Sweep Generator Woes
PostPosted: May Fri 21, 2004 6:17 am 
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J Matahratz wrote:
<font>quote:</font><HR><B>If there's no tuned circuit ahead of the detector, the output would always be at the same level, wouldn't it? So you'd get a straight line, which is what you have? Sounds normal.</B><HR>
<P>That's what I was thinking. But I tried hooking it to an FM tuner, and still couldn't get the proper trace. <P>
J Matahratz wrote:
<font>quote:</font><HR> <B><P>Have you recapped it and/or done any sort of inspection or check out yet? I've bought a number of pieces of "vintage" test gear over the past year - some looked awful on arrival and some looked new, but I don't think any of them worked properly right off the bat.<P>I don't have a manual. Did you find yours online?<P></B><HR>
<P>I've taken it apart and re-calibrated the marker generator. Oh, and I had to replace a bad electrolytic. That's about it. There aren't any paper capacitors inside, just a bunch of ceramics and some mylars -- the kind that "never go bad". I might go ahead check them just for the heck of it. <P>I don't have the manual for this model, but I did download the manual for the 368 from BAMA. The two models are not the same, but I did find it helpful.<P>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Fri 21, 2004 6:32 am 
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Leigh wrote:
<font>quote:</font><HR>Originally posted by J Matahratz:<BR><B>That's what I was thinking. But I tried hooking it to an FM tuner, and still couldn't get the proper trace.</B><HR>
<P>Sweep generators are used to characterize a single tuned circuit, or a small number of circuits in series which operate on the same frequency, like an IF strip.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR><A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A> | | <A HREF="http://www.Synchrophase.info" TARGET=_blank>http://www.Synchrophase.info</A>


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 Post subject: Sweep Generator Woes
PostPosted: May Fri 21, 2004 7:43 am 
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J Matahratz wrote:
<font>quote:</font><HR>Originally posted by Leigh:<BR><B> <BLOCKQUOTE><font>quote:</font><HR>Originally posted by J Matahratz:<BR>That's what I was thinking. But I tried hooking it to an FM tuner, and still couldn't get the proper trace.</B><HR></BLOCKQUOTE><P>Sweep generators are used to characterize a single tuned circuit, or a small number of circuits in series which operate on the same frequency, like an IF strip.<P><HR>
<P>That's what I was trying to do. I had the sweep generator and scope connected exactly as described in the Sams Phototfact. <P>I will admit, I've never used a sweep generator before, so maybe I'm missing something. <P>I'm stumped! <P>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Fri 21, 2004 8:26 pm 
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For starters, try sweeping an IF transformer by itself (no radio). Or if the Eico won't go down that low, rig up a simple L-C parallel cicuit and sweep that, fed through series resistors to reduce loading by the test gear. You should see a peak in the response somewhere.<P>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Fri 21, 2004 11:12 pm 
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J Matahratz wrote:
<font>quote:</font><HR>Originally posted by Alan Douglas:<BR><B>For starters, try sweeping an IF transformer by itself (no radio). Or if the Eico won't go down that low, rig up a simple L-C parallel cicuit and sweep that, fed through series resistors to reduce loading by the test gear. You should see a peak in the response somewhere.<P></B><HR>
<P>I think I have a NOS 10.7 Mhz IF transformer floating around here somewhere. <P>Apart from the transformer, do I need any additional components for this? Or do I just feed the swept RF to the transformer primary and connect the scope's vertical input to the secondary?<P>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Sat 22, 2004 12:44 am 
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I guess I'm a bit confused by this thread. Is the unit producing any signal at all? With the sweep width turned down, do you see a normal RF waveform? You described a nice rectangular pattern, so it seems like answer is yes. If so, it it only the sweep function that's not working? I'm unclear about what the symptom is. Like others said above, the sweep function is used to test filter response, if there's no filter between the 369 and the scope, there would be no droop and a scope pattern would be rectangular. (I think you could still see the sweep action, though the scope sync might do funny things.)<P>Anyway, your post inspired me to give my own 369 a try, but I found that the output is dead, and also the bandswitch is totally frozen up. (I hope a touch of WD-40 or something can loosen it, because otherwise it probably has to come out and be disassembled which, with the tricky RF wiring going to it, looks to be quite a job.) You may have yours working before me.<P>I see 2 large wax caps, 1 black tubular, 2 electrolytics, and the one dual can cap. I will probably replace all of them on general principles. That said, the problem you are reportring doesn't sound like it would be caused by one of those caps anyway.<P>J, any chance you could email me your file for the 368 manual? (Since you already have it, maybe you can save me from a BAMA download headache <IMG SRC="http://antiqueradios.com/forums/smile.gif">)<P>Does anyone know the difference between the 368 and 369? Does anyone know where to get a 369 manual from? Wow a lot of questions and this isn't even my thread.<P>Well good luck, wish I could be more helpful. I'm afraid I may be just adding to the unknowns on your topic, rather than answering questions! Well, if I get mine working I'll try my best to help out.<P>------------------


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 Post subject: Sweep Generator Woes
PostPosted: May Sat 22, 2004 1:55 am 
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Location: Pocasset, Cape Cod, MA
<B>>> think I have a NOS 10.7 Mhz IF transformer floating around here somewhere.<BR>Apart from the transformer, do I need any additional components for this? Or do I just feed the swept RF to the transformer primary and connect the scope's vertical input to the secondary?</B><P>It's been a long time since I played around with a bare-bones sweep setup. But as far as I recall, if you do as you described, and lock the scope sweep to the generator (30 or 60Hz, I don't recall), you'll get a solid screen full of RF with the transformer response curve superimposed. Sorry I can't think of a way to describe the pattern in words. If you insert your wideband detector between the transformer and scope, you'll see just the top surface of this screenfull (in other words the recovered audio modulation). You can see the transformer response either way, but the detected curve is easier to work with.<P>You can think it through, by assuming DC sweep: pretend the generator has a knob that controls the frequency and simultaneously supplies a DC voltage that controls the position of the scope beam from left to right. In fact some sweep generators <I>do</I> have DC sweep: my Texscan VS50 for instance. Except for the scope trace fading out, you can do a sweep at any rate you want, down to DC. Add a storage scope, and it works fine for very sharp crystal filters.<P>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Sat 22, 2004 2:08 am 
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Dave,<P>My unit is producing an output, but I'm not sure it is sweeping properly. But again, maybe there's nothing wrong with it at all and I'm just overlooking something that should be obvious.<P>The circuits for the 368 and 369 look electrically similar, but they definitely are not identical. I'm not sure the 368 schematic will helpful if you need to do a major overhaul of your unit. But the basic operating and calibration principles described should apply to both models. <P>I would email you a copy of the model 368 manual, but your email address is not listed! Have you tried downloading the manual from BAMA's mirror site? <A HREF="http://bama.edebris.com/manuals/eico/368/" TARGET=_blank>http://bama.edebris.com/manuals/eico/368/</A> <P>Good luck with your unit!<P>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Sat 22, 2004 5:43 am 
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I think I <I>might</I> be on the right track now. Again, I tried feeding swept RF into the IF strip of the Pilotuner T-601A, and this time I have what looks like a semi-decent trace... but it's upside down!<P>Take a look:<BR> <A HREF="http://antiqueradios.com/gallery/view_photo.php?set_albumName=Misc&id=scope_trace" TARGET=_blank>http://antiqueradios.com/gallery/view_photo.php?set_albumName=Misc&id=scope_trace</A> <P><P>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Sat 22, 2004 6:56 am 
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Reverse the diode in your detector, or flip the invert switch on the scope vertical channel, if it has one.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR><A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A> | | <A HREF="http://www.Synchrophase.info" TARGET=_blank>http://www.Synchrophase.info</A>


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 Post subject: Sweep Generator Woes
PostPosted: May Sat 22, 2004 7:16 am 
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J, looks like you're in the home stretch! Congratulations. As Leigh said, the upside down waveform is kind of a separate issue, the output of the generator is symmetrical and the polarity of what's seen on the scope just depends on the detector and the way the scope is set up.<P>I pulled my band switch - was able to unscrew the round posts and get the rotor part out without unsoldering anything - but it acts like it's welded stuck, won't budge at all. I'll look for a surplus switch of the same style and cannibalize the parts I need. Mine is turning into a project, glad you had better luck.<P>My email address is turned on now. I have gotten emails from other forum members, so puzzled that it was hidden today. Getting those BAMA manuals is extra problematic for me because my computers are Mac, and the Mac browsers don't seem compatible with Deja Viewer. However, my wife let me *borrow* her HP, and I DL'd it. Would still like the 369 version though, will keep looking around and will get you a copy if I find one.<P>------------------


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 Post subject: Sweep Generator Woes
PostPosted: May Sat 22, 2004 7:38 pm 
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J Matahratz wrote:
<font>quote:</font><HR>Originally posted by DavidK:<BR><B>J, looks like you're in the home stretch! Congratulations. As Leigh said, the upside down waveform is kind of a separate issue, the output of the generator is symmetrical and the polarity of what's seen on the scope just depends on the detector and the way the scope is set up.<P>I pulled my band switch - was able to unscrew the round posts and get the rotor part out without unsoldering anything - but it acts like it's welded stuck, won't budge at all. I'll look for a surplus switch of the same style and cannibalize the parts I need. Mine is turning into a project, glad you had better luck.<P>My email address is turned on now. I have gotten emails from other forum members, so puzzled that it was hidden today. Getting those BAMA manuals is extra problematic for me because my computers are Mac, and the Mac browsers don't seem compatible with Deja Viewer. However, my wife let me *borrow* her HP, and I DL'd it. Would still like the 369 version though, will keep looking around and will get you a copy if I find one.<P></B><HR>
<P>What part of the switch is binding up? I would think that as long as the wafers are intact, there's still hope. If it IS beyond repair, I don't know where you'd be able to find a suitable replacement, other than from a junker. I did luck out here; the inside of my unit looks almost as good as the day it was built. <P>Just out of curiosity, what tubes are in your unit? Mine has a few replacements. Lacking a schematic or a manual, I'm not sure they're the correct type. <P>If you do come across a 369 manual, I really would appreciate a copy. Likewise, if I find one before you do, I'll send you a copy.<P>Thanks for your help, everyone!<BR><P>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Sat 22, 2004 8:57 pm 
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Location: Pocasset, Cape Cod, MA
To fix your jammed switch, remove the C washer that holds the shaft in the threaded bushing. You can push it sideways off the shaft with a sharp pair of long-nose pliers (I admit it's tricky). Then push the shaft out, clean and regrease it, and reinstall everything.<P>By the way, this works:<BR> <IMG SRC="http://antiqueradios.com/albums/Misc/scope_trace.jpg"> <P>but I'll be darned if I can get the previously-quoted URL to display properly: the window is three feet wide and there's no photo anywhere.<BR>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Sun 23, 2004 8:13 am 
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Alan, I hadn't even to thought to take apart the sleeve assembly of that switch, good idea. After reading your remark I tried, but even with the C clip off, I couldn't get anything to budge in the slightest, even using all my strength. That thing is really stuck! What's binding is the shaft inside the threaded bushing that mounts to the panel. Like I said, I removed that part from the wafers, it's now soaking in acetone, maybe that will help. If not there's a big electronics surplus place nearby with a whole wall of rotary switches, I'm pretty sure I could find a similar one and just steal the rotor part from it. The wafers and switch contacts are fine, though they needed a LOT of cleaning before I got continuity.<P>Hey guys, I have a question, does anyone know what the unmarked neon lamp on the front panel is for? At first I figured it was just a power lamp but following the wires makes me think it's something else. I don't see any AC or DC voltage across it. One side seems to go to the "increductor" in the sweep section. (Weird term I know, but that's what the manual calls it.) J, does yours light up at all?<P>I finished recapping and cleaning it, and it seems to work fine. I replaced the funky mic connectors with BNC's. With the bandswitch still disassembled it's not quite ready for prime time, but hopefully it will be soon.<P>The tubes in my unit are all Eico so they are probably all original. The lineup is a 6BQ7 in the RF tuning assembly, a 12AT7 in the marker assembly, a 6X4 rectifier, and a 12AU7, 12AX7, and 6DR7 on the main chassis.<P>------------------


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 Post subject: Sweep Generator Woes
PostPosted: May Sun 23, 2004 12:53 pm 
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Hi J--<BR>One thing you might check is if you are using a direct input probe on your scope or a 10 to 1 divider probe; the latter is what you want, as direct input may distort the waveform because of attenuation. Also, set you scope to AC input, not DC. Good luck.<P>------------------<BR>


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 Post subject: Sweep Generator Woes
PostPosted: May Sun 23, 2004 4:24 pm 
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Location: Pocasset, Cape Cod, MA
It's old grease inside that shaft. Acetone is good; heat it with a soldering iron and it will eventually come free.<P>------------------<BR>


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