Eico 460 Oscilloscope Resurrection

[grantofalltrades]

Greetings folks!

I've been having a swell time lurking & thought I'd hop on board to get some opinions.  I apologize if this is the wrong board, I've been hemming and hawing on whether to put this under Test Equipment or Projects/Designs.

I've picked up an old Eico 460 Oscilloscope, in great condition - just needs some suspension work; and shocks, and brakes, brake pads, lining, steering box, transmission, rear end...

Well, I've cleaned out the spider webs and dust, and now I'm looking to get it spiffed up.  I plan on replacing all the old wax capacitors and getting rid of wires with old & brittle insulation.  I'm curious about how to handle the power, though, so this is where I am looking for guidance.

To start, the original power line was an old non-polarized 2-wire lamp cord.  The wiring schematic in the operators manual shows power going to the switch, then the fuse, then around the transformer & back:


In reality, the power is run to the fuse, around the transformer, to the switch & back out like this:


The problem I'm seeing is that if something shorts out, being non-polarized, that hot line could be bridged to the metal chassis and through the nearest bystander to earth with no fuse in the circuit.

To remedy, I've snipped out the old cord & dropped in a C14 connector for your standard 3-prong plug.  Once I tie that in, I can be reasonably sure the hot line will go to the fuse first.


So the meat of my issue now is: Should I do anything with the earth conductor, or leave the box ungrounded?


As things are currently wired, the chassis is acting as the ground - the circuits are tied to the metal frame to feed back into the transformer:



I'm wondering if I should break those from grounding to the frame, to instead ground via wired connections to the transformer; and then bond the chassis to Earth via the C14 connection...

Or should I skip the middleman & just light the thing on fire and stick a fork in an outlet?

[N2IXK]

Welcome to the EEVBlog forums!

Good call on modernizing the AC power wiring.  I would definitely tie the IEC ground pin directly to the chassis, using good heavy wire. Shakeproof washer and crimp lug.  Modern scopes are made this way today. Earth ground is directly connected to the ground shell of the BNC input connectors.

AC power "hot" should go to fuse first (rear terminal of fuseholder), then to the switch, and then on to the transformer primary.  Neutral side of line direct to other end of primary.

Definitely replace all the old tubular paper caps, as well as the multisection electrolytic.  Materials science wasn't very advanced when that thing was made, and the dielectric paper used in capacitors tends to develop leakage over the years.  Ceramic and mica caps aged much more gracefully, and don't need replacement unless there is a provable failure.  A couple of the tubulars are high voltage types, and they will be a bit expensive and harder to find. than common 600V film caps. Leaky caps will cause all kinds of hard to find issues, and an electrolytic shorting out can smoke the power transformer.

If you need any parts, I may be able to help. I parted one of these things out a few months ago, and held on to most of the switches, pots, transformer, CRT,  etc.

What are you planning to do with this thing? I have a fondness for old hollow state gear, but you should realize that a similar vintage Tektronix or HP or even DuMont would cost about the same to recap and restore, and you would end up with a much better scope. The Eico 460 was touted as a "wideband" scope, with a 4.5 MHz bandwidth., it was targeted at the color TV repair market, as it had enough bandwidth to view chroma signals in NTSC sets. It doesn't have triggered (or even calibrated) sweep, the sync is fairly touchy, and the low voltage CRT produces a dim fuzzy trace compared to better scopes. Your unit looks to have been built from a kit (tube sockets screwed in rather than riveted), so be on the lookout for sloppy wiring or other mistakes by the original builder.

Had a beat-up Eico 460 as a kid back in the '80s . Found it at a yard sale for $10.  Not much for real measurements, but it sure looked cool hooked to a stereo system producing Lissajous patterns...

[grantofalltrades]

Thanks for the welcome, N2IXK 

I don't have much of a plan for the unit, honestly.  I've got a Tektronix 465 and an RCA 535 for working scopes... I bought this one mostly as a project piece.  I really just want to take my time dissecting it & learning how all the pieces work together.  If I can get it working again, it'll probably live out the rest of its life attached to a stereo just looking cool.

I hadn't even thought about the possibility that this was a kit build, but that would definitely explain some of the...er... eccentricities.  You don't have to look too hard to find that sloppy wiring.

I appreciate all the great info.  I'll be taking a million pics during the process, so I'll hopefully be able to return with a good project post in the future.

Thanks again!

[dentaku]

I tore one of those apart and salvaged the switches and knobs from it.
It was in terrible condition so it wasn't worth trying to fix it.

[SoundTech-LG]

That was my DreamScope in 7th grade. Built a nice walnut enclosure for it in wood shop, but never found the time to build the rest from scratch.

[nathon]

I know this is an old post, but I just had to chime in. My dad knows I work with electronics so when he saw this sitting around in a 2nd hand store somewhere he just had to pick it up. I already have an HP scope that I use for most of my work, but this thing is pretty neat if for no other reason than to have it sitting on a shelf looking cool.

Anyway, it seems to be in great working order. I haven't cracked it open yet; I'm bracing myself for what was mentioned in the article. However, mine has a unique marking on it that looks military in nature. On the back it has painted in that military stenciling "IRAM Ø 50" and on the front one of those old raised labels that says "IRAM NO 50". I'm wondering what this was used for.

I found search results for IRAM in Google. One was for (I hope this doesn't get me on some watch list) an "IED" type device. The other was for Intelligent RAM. I know it's all academic at this point, but I enjoy knowing the history on old stuff like this. If anyone knows what this was from, please let me know.