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 Post subject: EICO 425 O'scope
PostPosted: Nov Sun 01, 2009 5:53 am 
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Location: Coram, New York 11727
OK, did it again! Place a maximum bid on this unit at $20.00 for the heck of it and won! Now I have the op manual from bama mirror site and schematic which has no values for resistors or caps, just the numbers (R12, C14, etc.). Does anyone have the parts list with the values? Can anyone tell me what items I should check first before spending any time or money restoring, I mean items that if shot can not be replaced. Also how can I determine if the CRT is any good other than checking heater and without trying to restore the unit only to find it is shot? Finally, is it worth restoring? PL


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PostPosted: Nov Sun 01, 2009 8:49 am 
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Hi there planigan---
OK, first off, the older scopes are really crude by standards of today. That is normal, and we obviously cannot expect a 425 to work as well as a Tek 547, simply no comparison. They are not extremely rare, but they are not common as dirt either. I would evaluate the current condition of the scope now, can you post pix ?

Also, I would take into consideration the following : If the scope is restorable, with a good case, what might you have to replace, caps for almost certain, and probably tubes too. The CRT may be good if someone has taken care of the scope, but it also might not. Then you must take into account how much time YOU would be willing to donate to the scope to see if return to life. What is it worth to you ? It may be a model that will be in demand in ten years, or not. In any case, the bottom line is this: Tube scopes are not made anymore, and with every passing year, they are most likely going to get rarer, so if I were you, I would seriously consider preserving an otherwise unwanted orphan from an almost certain death in a dumpster ! :shock: :shock: :shock:

I am of the mind, and others here will probably agree with me, that we collectors and restorers are preserving the technology of the past for future generations. It is not necessarily a calling or a duty, but it is what we do, and damn it's fun ! By preserving what we can of the past, we prove in this modern world that the old gold still CAN and WILL work, contrary to what people may think.

I would restore that scope, even though you may not have any practical use for, who knows ? There may be a newbie to our great hobby that is looking for a piece of old test gear that he can cut his teeth on,.......

Good luck !

----Tom

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 Post subject: Re: EICO 425 O'scope
PostPosted: Nov Sun 01, 2009 9:04 am 
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planigan wrote:
OK, did it again! Place a maximum bid on this unit at $20.00 for the heck of it and won! Now I have the op manual from bama mirror site and schematic which has no values for resistors or caps, just the numbers (R12, C14, etc.). Does anyone have the parts list with the values? Can anyone tell me what items I should check first before spending any time or money restoring, I mean items that if shot can not be replaced. Also how can I determine if the CRT is any good other than checking heater and without trying to restore the unit only to find it is shot? Finally, is it worth restoring? PL



I normally don't use a schematic for resistor values, unluss they are damaged or blown apart. Not sure of the site right off, but Google resistor calculator, and I believe it's the first one. Like was already said replace the caps, and check the tubes before you replace them. My EICO 460 scope was bought in semi working condition, and had been used daily for years before the previous owner had gotten it, then it sat for a couple years.

All the tubes, except one checked good, and caps were replaced. Most of the resistors checked good, and were figured with that calculator I mentioned.

Do the caps, clean the pots, and check the tubes. It will more than likely be fine to use, and be pretty well accurate for what it is. My 460 is nearly dead on when checking voltages, and wave forms.

Good Luck.

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 Post subject:
PostPosted: Nov Sun 01, 2009 2:28 pm 
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There are only two parts, aside from the sheet metal, that are really "unobtainium" here, the CRT and the power transformer.

You can easily check the transformer with an ohm meter. Pull all the tubes, check the low voltage secondaries, and check the HV secondary from V4 pin 6, to V3 pin 2.

As for the CRT, you'll have to get the power supply running before you can check it at all. At that point you can at least verify a spot on the CRT face and determine it will move with the vertical and horizontal controls, and that it will focus and change intensity. Just the rectifiers and CRT installed of course.

Mechanical stuff is the least dependable of all, so be sure to clean and exercise all the pots, connectors, switches and tube sockets/pins, before you do ANY Live tests. If all is well at this point, you're maybe half way to getting it running, and a couple hours spent so far.

Mike


Last edited by Mikeinkcmo on Nov Sun 01, 2009 3:43 pm, edited 1 time in total.

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 Post subject:
PostPosted: Nov Sun 01, 2009 3:10 pm 
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planigan - I think I have just what you need. I'm emailing you a scanned copy of the assembly manual for the 425. This includes a parts list, voltage chart, schematic, and detailed assembly instructions.

I'm also sending you a copy of the schematic that I redrew a few years ago. It's just a little easier to follow.

As mentioned, the 425 is a very basic scope... no triggering or calibrated anything. I keep mine around just because I think it's cool.

One important note. Be careful around the filament of the CRT when power is applied. It's sitting at about -1300 Volts. That'll hurt.

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 Post subject:
PostPosted: Nov Sun 01, 2009 3:23 pm 
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I just finished restoring an EICO 425 about two weeks ago and it is working fine. I needed a CRT (5BP1) and obtained one from a fellow forum member. After you are sure the transformer is useable, change "ALL" the capacitors. I tried to do most of them and was bringing the 'scope up on a variac when one of the chassis mounted, oil filled, caps began to leak. I lost my initial trace at that point and shut down. The caps in question are box-shaped and bolted to the chassis. After I changed them all was well and the 'scope works fine now. You don't need to install the same type and there is lots of room under the chassis to mount large caps. I used terminal strips to hold the replacements for the oil filled caps. You may have to order the high voltage caps that are near the CRT socket. I was lucky and had some on-hand. I then made a probe from EICO instructions and again was lucky having all the parts on-hand. It works fine with a good trace. I feel it's worth the effort to restore any of the old test equipment. There is too much of it being tossed and lost to the hobby.

Pat

P.S. Thanks to Phil (previous entry) I was able to get clearer schematics to work from. If you need the probe information send me a PM with your email address.


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 Post subject:
PostPosted: Nov Mon 02, 2009 4:46 am 
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Thanks guys for the responses. Phil that was very nice of you to e-mail the schematic plus manuals. Just before I logged on and saw the responses I had gotten my hands on a tube pin-out and checked the heater on the CRT = open. I did notice that the base was loose and that the tube is mounted so that its face rests in the face panel of the unit and the rear by the socket. I may unsolder the base and see if the leads are possible broken from flexing. Barring that the tube is shot. Have not checked Xfmr yet but looking at the chassis and the Xfmr leads me to believe its OK as the paint on it is still shiny, no evidence of heat, of course that's not proof positive. The set must have been stored in a relatively clean and dry environment as the chassis looks new, no evidence that it was restored to that condition. Definately a kit, all sockets bolted to chassis (factory usually riveted). I'm going to have to think on this. The challenge of at least restoring the chassis and replacing the resistors and caps is intrigueing but would cost. A lot of resistors have common values but wattage in most cases is over 1 watt. Also have to consider guilt trip after what signalcorpsoperator stated! Understand there is a sub for CRT, I have CV601 and CV835 as subs but have not found out if they are physically the same, believe the sub only stated electrically the same. Put pictures in next. Like to hear your comments on how to proceed. PL ImageImage[img][img]http://i178.photobucket.com/albums/w265/planigan/IM000648.jpg[/img][/img]

PS: Sorry about case, I have an affinity for dark gray (battleship gray for the sailors out there) for test equipment. Image


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 Post subject:
PostPosted: Nov Mon 02, 2009 7:28 pm 
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planigan, you're very welcome. I can't offer anything more than has already been said as to how to proceed. Replace the paper caps and check resistor values. The resistor values are not that critical since they're all 20% and there's nothing calibrated on the scope. As to the wattage, I suspect that they just used what was available to them at the time the kits were packaged. Mine has a couple of 1/2 W and mostly 1 W (or more). I see yours is the same vintage as mine (very early 50's) since it has the blue front panel. I assume yours also has the "chicken head" knobs? IIRC the 425's were still being sold into the early 60's, but with a solid silver front panel and different knobs (picture at http://www.nostalgickitscentral.com/eic ... st/425.jpg ).

I agree with your observation that your scope has been stored well. Your front panel doesn't appear to show the wear that mine does. Also, I notice you have the original graticule that mine is missing. I'm curious: How is that fastened in there, or is it a friction fit? There's no mention of it in the assembly manual. I cut one out of an old Tektronix graticule that I had laying around and just kinda stuck it in the CRT hole, relying on the felt to hold it in place. :?

BTW, in 13 days, that schematic will be 60 years old (Drawn 11-15-49)

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 Post subject:
PostPosted: Nov Mon 02, 2009 11:30 pm 
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Hi there fellows---
Planigan -- I am sorry if I started a guilt trip on this scope, didn't mean to ! :? I was merely stating that we should try to preserve pieces if we can. Your scope is in definitely nice condition ! I think that the battleship gray, ( yes, I love it too ), looks pretty good with the blue front panel ! Not a bad idea for my case here, hmmm. Did you airbrush, spray can, or roller it on ? Looks really nice ! I am also curious as to whether or not the graticule is a friction fit. Mine is long gone, so I will either end up finding a scrap one to sub with, or start from scratch and make up a new one. Let us know how it turns out !

Tom

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 Post subject:
PostPosted: Nov Mon 02, 2009 11:41 pm 
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planigan,
It is worth restoring, in my opinion. I always liked the look of those old blue faced Eico instruments and have several (but not the scopes). You could always connect it to the output of your stereo and astound and amaze your friends.
Rick


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 Post subject:
PostPosted: Nov Tue 03, 2009 6:42 am 
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I'm still digging into it. I think the To the "unobtainium" list should be added the 2 4 Meg dual pots and possibly the 250K/1Meg dual pot. Since those pots work in tandem their critical. Can find dual 250K and dual 1Meg and think (dont know as I haven't examined parts) that you may be able to switch the rear pot on each and come out with a two 250K/1Meg. just order would be different. When it comes to the 4Meg, I can't find dual pots that high. Seen single 5Meg which might work but don't have the foggiest if you could "gang" them. One of the 4Meg dual on this unit open, will take apart and see if it can be repaired. Othe is high but should work. The 250K/1Meg has same problem.
Phil - yes it has the chicken head knobs. signalcorpsoperator - spray, can painter's touch (rustoleum) gloss dark gray, graticule (I would have called it "that graph thinggy") on circular piece plastic about .015 thick, just rests /held by felt liner in frt mounting ring. Will keep you informed of progress or lack there of. After the pots I'm sorta leaning toward not restoring. PL


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 Post subject:
PostPosted: Nov Tue 03, 2009 7:12 am 
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Hi there---
Thanks ! I really think that it turned out good, might end up doing the same thing with mine. OK on the pots, finding a dual section one with that kind of value might be a chore, another alternative would be to locate a parts unit ??? Not sure where you are located, but a local hamfest would be probably the best place to start looking for a parts set. Also, posting here on the ARF is great too ! Lots of folks that can offer ideas..... Good luck !

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 Post subject:
PostPosted: Nov Tue 03, 2009 8:03 pm 
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I wouldn't worry too much about the value of those pots. If one or both reads high or low, you wouldn't even notice it in operation. While it may look complicated, all those pots do is vary the potential on the horizontal and vertical deflection plates of the CRT. (Horizontal and vertical position.) The pots (all 4 of them) are just in parallel between a positive supply (B3) of around +200 Volts and a negative supply of around -140 Volts. When the pots are turned, they apply a more positve voltage to one plate and a more negative voltage to the opposite plate. You'll notice, that about mid-range on the pots, the bias applied to the CRT deflection plates will be about 0 Volts. The only thing to be concerned about is their overall parallel resistance, in this case, about 1 Meg. If you draw the circuit out, you'll probably see what I'm talking about.

R40, the 250K/1 Meg dual pot, is also not critical as to value. The 1 Meg controls the sweep speed and the 250K controls the retrace, keeping a ratio of about 20:1. Remember, this scope is not calibrated in any way, shape or form. Hopefully, all they'll need is a good cleaning.

Thanks for confirming my suspicions on the "mounting" of the "graph thingy" :? . I guess I was hoping for a more elegant solution, but if that's the way they built it, that's good enough for me.

Don't let the problems get you down. Remember, this is supposed to be fun. If it's too much like work, set it aside for a while and play with something else. It's waited well over 50 years, a few more won't hurt. :)

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 Post subject:
PostPosted: Nov Sat 07, 2009 6:55 am 
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Well, opened up the dual 4 Meg and and the front pot resistive path is gone, zero ziltch. Removed xfmr and was able to ohm out and finally get leads sorted. It has three filiment secondarys and the HV secondary whic I believe is 1400-1500 V. Will check out voltages and then CRT base for (hopefully) broken lead wire. Not looking good. PL


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 Post subject:
PostPosted: Nov Tue 10, 2009 7:46 am 
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Checked out the xfmr, had to remove from chassis to check all leads. Started to check in unit and realized if the wiring was done incorrectly I be in error. Had a suprise, didn't take not of Phil Weising's notation of 1400V on schematic and after pegging my DMM (500V Max) and EICO 221 (1000V) VTVM realized I don't have a meter that reaDS OVER 1000V but judging from the sparksI believe the HV on that xfmr has 1500V, then there are three filiment lines and the HV for B+. Sorted them all out and xfmr is in excellant shape, paint work even shines like new, no evidence it was ever used other than length of leeds (one set about a foot long to reach rear of CRT). Removed base of CRT checked all leads from tube and no continuity between any of them - heater open!
Thank you for all your advise, and signalcorpsoperator, I was only funning you about guilt trip, sorry if you took it seriously. I going to parts it out and see if I can recoup some of my money. Thanks again for the assistance. PL


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 Post subject:
PostPosted: Nov Tue 10, 2009 10:33 am 
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Hey there Planigan---
No problem buddy ! I knew your were joking, I kinda went along with it, lol. Anyway, good to hear that the transformer is in excellent shape, most of the ones that I have seen have definitely had better days ! OK on the parting out of the unit, not all good things will last forever, :wink: . I hope that you are able to successfully recover some of the money that you spent on this scope ! Good luck !

Regards---
Tom

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 Post subject:
PostPosted: Nov Sat 14, 2009 7:14 pm 
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Why not wait and see if you can find a new crt at a later date. I have seen new ones on ebay from time to time athough they may not be very good.I just got a scope for parts that has a 5bp1 crt with it.The guy said do you want the crt and I said sure.I don't know if its good but I try it in my 425 sometime in the future.


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 Post subject:
PostPosted: Aug Tue 24, 2010 12:07 am 
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A few years ago I acquired an Eico 425 with the silver panel. It has been sitting in the garage ever since. I have not powered it up, although my buddy seemed to think it was working when he put it on the shelf back in the early 90s. Empowered with the knowledge of the previous posts (not to mention guilt) I am going to open it up and check it out, transformer first. I'll try to keep everyone posted (for entertainment value) and I'll reach out for advice as needed.
Thanks in advance,
Gary


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 Post subject:
PostPosted: Aug Tue 31, 2010 8:34 pm 
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5BP1 is an extremely common scope CRT. Was used in lots of models besides the Eico 425. Shouldn't be that hard to find another, especially if you are willing to settle for a good, used pull.

But before you toss the old CRT, take a soldering iron and some solder, and re-heat the pins of the phenolic base of the tube--especially if it is a little loose. They are notorious for cold solder joints. You may find that the heater is actually still good.

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 Post subject:
PostPosted: Dec Thu 30, 2010 12:12 am 
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Location: Colorado Springs
I have an original user's manual for the Eico 425, free (in the U.S.) to the first asker.
It's just a little booklet, about 5 X 7 inches.
The last page has a schematic.

The 425 was my first scope - got it from my junior high school electronics teacher in about 1974.

Pete


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