Eico 460 Oscilloscope - Videokarma.org TV - Video

darklife · #1 02-12-2011, 03:50 AM

Anyone here own one of these oldies?

Got mine a few years back for 20 bucks and it has worked great until one of the HV capacitors for the CRT died. After replacing it all was good for a while.
Tonight same thing happened again. Using it for a good hour and suddenly buzzzz snap and there goes the fuse.
Opened it up and sure enough the other capacitor out of the two for the 1500v supply went.

So I got to thinking what could possibly be taking these caps out? After a bit of research I found that they were installed backwards since the day I got it!
Even though they are .1uf 1600v caps the fact that their polarity was reversed must have been what made them go?
They had both of neg. of caps going to chassis and positive to the HV tube. I did a quick power up HV check using a multimeter and sure enough they were suppose to be installed the other way around with pos. going to chassis and neg. going to the HV tube.

Do you think this may be why the capacitors died?
Also the power transformer in this gets very hot. I read in a few other places that it's common for the transformer to burn up in time. Any way to prevent this? The manual says 115v operation, my wall is around 125. Maybe that's why the transformer gets hot

This is such an old scope but I like it for the simplicity. Hope to do a full recap and check for aged resistors when I get the time. As of now it's working "okay".

Findm-Keepm · #2 02-12-2011, 08:23 AM

The Eico 460 was a flagship product for Eico for many years. There used to be an Eico 460 enthusiast site on Geocities years ago. I found it when researching my first 460 - I've got two, only one of which is working. I resored it as a winter project back in 2001/2002.

Most likely, your old 1500V supply caps just died - my recommendation is to not use it until a full recap is done. The higher line voltage doesn't seem to bother mine a bit - I have 127V at the outlet in my garage shop. I'll admit that I've never felt the transformer for temps, though.

Many other tube based oscopes are out there - I've got several Heaths, an RCA, a Dumont, and a Knightkit, which is my next restoration. They're very easy to work on, and their boxy cabinets make them easy to store under the bench.

Eico made a model 488 "switch" - a separate unit that would allow any Oscope to become dual channel. I have one somewhere, and have never tried to use it. Great accessory if you are using it to troubleshoot input vs. output in audio circuits.

Congrats on a great find.

Cheers,

bob91343 · #3 02-12-2011, 11:49 AM

You can put in a bucking transformer to lower the power line voltage and extend the life of the components.

There is no polarity on those paper capacitors. Either way you hook them up they are okay.

I have a Dumont 401R that I'd love to sell. It needs one capacitor, the funny one in the power supply that resonates the power transformer (constant voltage transformer). Otherwise I believe it's fine. Been sitting on the patio for years now and I might just part it out. I have manuals, schematics, etc. and got some good use out of it before I got my Tektronix.

darklife · #4 02-12-2011, 03:53 PM

Thanks for the replies so far. I will look around my junk boxes and see if I can find an old transformer that will work as a "bucking transformer". I just don't feel comfortable with how warm the power transformer runs but I don't know maybe it was made to handle that much heat. It gets almost too hot to touch after an hour of operation while inside the cabinet.
I have had a lot of older scopes in the past but this one is by far one of my favorites for some odd reason. It's simple to repair and gets the job done for basic audio testing and some low frequency RF work. Could always get a new scope but I like antiques what can I say

Another problem I notice is that on a few of the sweep selector ranges the waveform gets more narrow toward the left of the CRT, and wider toward the right. Just enough to be noticeable to the eye. I wonder if the sweep oscillator needs a tuneup or maybe has an old capacitor that is acting funny?
It only seems to happen on the 1-10k range.

I don't really have any other projects going for me right now so I plan on tinkering around with this until it works really good. Do a few modifications to make it run better and recap it so it runs as new. Besides this is teaching me a lot about the internals of how an oscilloscope operates so it's an educational project for me.

Any further ideas or suggestions are appreciated.

Findm-Keepm · #5 02-12-2011, 05:46 PM

Quote:

Originally Posted by darklife

Thanks for the replies so far. I will look around my junk boxes and see if I can find an old transformer that will work as a "bucking transformer". I just don't feel comfortable with how warm the power transformer runs but I don't know maybe it was made to handle that much heat. It gets almost too hot to touch after an hour of operation while inside the cabinet.

Another problem I notice is that on a few of the sweep selector ranges the waveform gets more narrow toward the left of the CRT, and wider toward the right. Just enough to be noticeable to the eye. I wonder if the sweep oscillator needs a tuneup or maybe has an old capacitor that is acting funny?
It only seems to happen on the 1-10k range.

I don't really have any other projects going for me right now so I plan on tinkering around with this until it works really good. Do a few modifications to make it run better and recap it so it runs as new. Besides this is teaching me a lot about the internals of how an oscilloscope operates so it's an educational project for me.

Any further ideas or suggestions are appreciated.

There are thousands of these out there working on the higher line voltage with no problems. Definitely do the recap - the B+ filter caps, even with the slightest leakage could cause the tranny to get hot. Even a few milliamps of leakage at 375 Volts could equal several watts. I fired off my 460 this afternoon - it hasn't run in about a year and a half, and it woke up fine. The tranny was barely warm after 20 minutes. I put her back together a hour or so later, and the tranny was just warm, not hot. I'd replace the 20/20/20 @450 with some 22uF@450 caps and see if that cools it down some.

Cheers,

darklife · #6 03-07-2011, 08:30 PM

Well the problem is coming back again. The first .1mfd 1600v capacitor before the filter resistor is starting to make that arcing sound. At least I think it's coming from the cap. It sounds like a few snapping sounds when I first turn on the scope.

When this happened before it wasn't long after that the capacitor shorted out causing the PS fuse to blow.
I know there shouldn't be no >1600v on those capacitors, yet they keep doing this. First it was the wax cap that went bad (yes I know wax caps are bad anyways), then a black plastic one rated at 1600v which I replaced. The schematic calls for 1000v cap for filter,... so WHY does these 1600v ones keep snapping and then shorting on me?

How do I measure the HV on this? My multimeter only measures up to 1000DC and I really don't trust my meter for this kind of stuff.
I would like to measure the HV output to see if it's really above what the capacitors can handle.
I also notice that the scope goes to blooming trace on anything above half way up on the intensity control. So it's getting a lot of HV is my guess.

The scope is working fine still but I know it's days are limited until I figure this out. It's only a matter of time before it eats another HV capacitor which lucky me I am now completely out of replacement parts for.
As soon as I heard that internal snapping sound in the past it wasn't long after that the HV capacitor shorted. I don't see any physical arcing and I swear the arc sounds like it comes from inside the capacitor.
These capacitors are new BTW.

Also finding HV capacitors are not easy today. Is there any practical way to string up higher mfd capacitors at lower voltage to equal .1mfd to get to the voltage/filtering value it needs?
Like taking -----)|---)|---)|-----
Each one being rated 600v to total a 1800v handling capability?
Excuse my ascii, but something like that?
I believe high value resistors would need to be wired in parallel with each cap to equal out the voltage across each capacitor correct?
I know in transmitters the HV supply for the power amplifier tube is sometimes wired that way for HV filtering.

Ugh sorry for the long post and questions. You guys rock for info.
I should just get myself a good oscilloscope and toss this thing into the corner but right now this is all I have to work with

Findm-Keepm · #7 03-07-2011, 10:08 PM

Quote:

Originally Posted by darklife

Also finding HV capacitors are not easy today. (

Start with Allied Electronics - look at the ASC HV caps on page 1677 of their catalog. I can highly recommend them - I get caps from them from time to time.

http://www.alliedelec.com/catalog/pf.aspx?FN=1677.pdf

Cheers,

wkand · #8 03-27-2011, 11:37 PM

I had the same issue with a ceramic body tubular axial cap used in the 120 v input side of the x-former. I bought some ceramic discs from RS and connected them in parallel (remember: capacitors add in parallel, resistors in series) I dont recall the values anymore, but it worked. It's not pretty, but it can aid you in determining if that solved the issue.

I agree with the hot transformer comments. Replace those electrolytics ASAP!!

Walt