Hey everyone!

So I have a treat for you all tonight. Yesterday evening I posted an ad on Craigslist titled "Wanted: Electronic Test Equipment". This morning I found an email in my inbox saying a gentleman that lived just up the road from my apartment in Boston, saying his father-in-law, who was an electrical/mechanical engineer who schooled at MIT in the '50s, had just passed away and left all his old equipment in this gentleman's basement. He wanted to get rid of it to make room for a house renovation. I ended up finding the following items, along with dozens of other pieces of equipment that I had to turn down for multiple reasons.


Above is an RCA RF signal generator (left) and an Eico tube multimeter (right).


This is an audio generator. Unfortunately the square wave side doesn't work, but the sine wave side does. I also found another one, a bit older (with vacuum tubes), which is fully functional:



Here are some miscellaneous items I picked up, including Resistance and Capacitance boxes, a newer analog multimeter, portable adjustable power supply, and a resistance wheel:





I'm going to have to split this up into a second post, since I'm only allowed 6 attachments per post.

 

The last two items are probably my favorites from this haul.

First is a capacitor tester, which is enclosed in a beautiful wooden box and is in excellent physical condition. I have not been able to test it yet, so I don't know if it works or not:



The last one is the crowning jewel of this collection, and the one I'm most proud of: A Central Scientific Company oscilloscope, I'm guessing from the '50s or '60s. I am actually hoping to find more information on this particular model--when exactly it was made, etc:



Unfortunately, when I plugged it in and turned it on nothing showed up on the screen. I opened it up and all the electronics (tubes, etc) seemed to be intact. However, it appears the CRT itself is damaged on the inside. I apologize ahead of time for the terrible photo, I have yet to get a decent camera:



I am guessing that burnt spot is the reason it's not working. I am curious if any of you guys know how much this thing might be worth, in working condition and in non-working condition.

So that's what I picked up today. Now for the fun part--the cost. I went in willing to pay $70 (looking for a small power supply and maybe some odds-and-ends, cables, etc). I felt awful for offering him so little for this mess, but I mentioned that's what I had, and that I'd be willing to thin out my selection slightly in order to make it more reasonable for him. I asked him what he would want for the whole lot, just to get an idea of how much I would need to remove from my "pile". His response? "$40".

I was blown away, and after making sure that he was serious, I gratefully accepted.

So what do you guys think? I think I did pretty well for the cost, even though some of the equipment doesn't work. Please feel free to comment on this, I'm curious what your opinions may be!

Regards,
Matt

 

Wow, $40.00? What a steal.

I grew up looking at old equipment like that, but never had the time to educate myself to understand what it was all about.

Had way too many irons in the fire to also learn electronics, but always admired the craftsmanship on those older wood and metal test instruments.

 

I actually built that EICO VTVM, somewhere in the 1960's. I threw it in the trash right after I bought my first Fluke DVM. It was just too slow to warm up, and not as accurate as a Fluke.

 

I actually built that EICO VTVM, somewhere in the 1960's. I threw it in the trash right after I bought my first Fluke DVM. It was just too slow to warm up, and not as accurate as a Fluke.

I haven't had a chance to fire this one up yet, the probe isn't in very good condition. I'll have to try it sometime soon though.

 

The corrosion on the scope looks like it has been in that basement collecting humidity and oxidation for a long time. Anything near the blue arc of electric motors may suffer accelerated oxidation from the ozone.

The enamel magnet wire on the coils may be corroded and shorting out. The insulation on the wires may be cloth, not rubber or polymer. Also, look for severe buildup of black copper(II) oxide on the switches - a complete mess on this old stuff. The caps will definately need some help.

I had a fun time restoring some high frequency signal generators, they had good bones to work with. Things like scopes have so many potential problems they become a work of love instead of a work of practicality. VTVMs are not worth the effort - low impedence inputs when a $5 meter from Harbor Freight does a better job.

 

Just remember to start it a half hour before you need it. The 12AX7 drifts badly and persistently during warm up. That one must have been designed as a bench instrument like the RCA Senior Volt-Ohmist because you can't wait half an hour for a voltmeter on a house call. That's what the Simpson 260 was for.

And remember to check the battery. I think it was a C cell or a D cell. Probably leaked and the acid melted the battery holder.

 

The corrosion on the scope looks like it has been in that basement collecting humidity and oxidation for a long time. Anything near the blue arc of electric motors may suffer accelerated oxidation from the ozone.

The enamel magnet wire on the coils may be corroded and shorting out. The insulation on the wires may be cloth, not rubber or polymer. Also, look for severe buildup of black copper(II) oxide on the switches - a complete mess on this old stuff.

Yes, it's not in very good shape, but I'm still excited just to have found this thing, working or not. The inside looks to be in decent condition, all things considered. Yes, the coating on the wires is made of cloth, but there is no rot, no burns, etc that I can see. After examining the inside of the scope, I really think it's simply a problem with the CRT itself, as mentioned before.

 

That "burnt spot" on the CRT is normal, that is not the problem.

There are two things you can check easily, the CRT heater filament and the HT supply which should be about 8kv.

You can test the heater filament when powered down, it should be low ohms (2 pins on the neck will be the heater). Then power it up, and the heater will get a low voltage DC or AC, and should also glow and give some warmth after a few minutes on the end of the neck.

The easiest HT check is to power it up for a few minutes, then power it down and quickly put a small metal screwdriver attached by a wire to the CRT ground strap or frame, under the rubber final anode cap. It should make a "crack" sound as the 8kv HT discharges from the tube capacitance through the screwdriver to the ground strap.

The HT circuits on small tube 'scopes are pretty simple, they use an NPN driver transistor into the flyback coil unit. (Collector to the bottom of the flyback coil, emitter to gnd, like driving a relay). You can scope the base waveform, and voltmeter the B+ voltage into the flyback unit which is likely about 80-100v DC.

Common faults are dry joints, corrosion/loose on the CRT neck pin socket and or other sockets, and power failures (there are probably fuses/fusibleresistors on all the voltage rails).

 

Nice haul Matt. You have some pieces of history there.

 

That "burnt spot" on the CRT is normal, that is not the problem.

There are two things you can check easily, the CRT heater filament and the HT supply which should be about 8kv.

You can test the heater filament when powered down, it should be low ohms (2 pins on the neck will be the heater). Then power it up, and the heater will get a low voltage DC or AC, and should also glow and give some warmth after a few minutes on the end of the neck.

The easiest HT check is to power it up for a few minutes, then power it down and quickly put a small metal screwdriver attached by a wire to the CRT ground strap or frame, under the rubber final anode cap. It should make a "crack" sound as the 8kv HT discharges from the tube capacitance through the screwdriver to the ground strap.

The HT circuits on small tube 'scopes are pretty simple, they use an NPN driver transistor into the flyback coil unit. (Collector to the bottom of the flyback coil, emitter to gnd, like driving a relay). You can scope the base waveform, and voltmeter the B+ voltage into the flyback unit which is likely about 80-100v DC.

Common faults are dry joints, corrosion/loose on the CRT neck pin socket and or other sockets, and power failures (there are probably fuses/fusibleresistors on all the voltage rails).

I'll check that out. The strange thing is that this CRT is set up much different from what I'm used to. I don't recall ever seeing the anode cap that you see on most CRTs. Also, there are no driver transistors here, just vacuum tubes. It was a pain to put back together after taking it apart, but I guess I'll disassemble it again and snap a few photos for you guys. I also want to take another look inside the thing myself...

Nice haul Matt. You have some pieces of history there.

Thanks Joe, I thought so too

 

D8, looks pretty cool. I like it when people reuse saving stuff from rotting at the dump.

Good job!

I couldn't do it, I'm not that good with electronics yet, good luck

kv

 

That "burnt spot" on the CRT is normal, that is not the problem.

I am used to seeing a silver spot if it's good, white if it's bad. Black does not make sense to me.

 

Hello,

The spot is made by the getter:
http://en.wikipedia.org/wiki/Getter

Normaly when air gets into a tube, it will go white.
That way you can see the vacuum has been broken.

Bertus

 

Hello,

The spot is made by the getter:
http://en.wikipedia.org/wiki/Getter

Normaly when air gets into a tube, it will go white.
That way you can see the vacuum has been broken.

Bertus

Thanks bertus. In that case, I would guess the tube is still evacuated of air, so that's a good thing. Someone on another forum mentioned the possibility of electrodes being shorted together. I'm going to pop it open and take a closer look, and take some measurements, in a few minutes. I'll let you know what I find.

 

Ok, so I took this thing apart again and snapped a few photos.

Here's the inside of the scope:

After looking at the tubes again I noticed one I hadn't noticed before: The rectifier tube has a large white spot at the top. I expect this means that air got in to the tube:

That tube also seems to heat up more quickly than the others, and stays warmer for a longer period of time after the scope is switched off. I have a feeling this rectifier is blown, which I believe would cause the display to not work at all. Am I correct in this assumption?

Thanks,
Matt

 

Ok, so I removed the tube and did notice a small crack in the glass, down near the base. I found a new one on ebay for $0.99, plus $6 shipping, so I went ahead and ordered that. I'll post some photos when I get this thing working

Regards,
Matt

 

Hello,

Yes, it looks like that tube has some air in it.
The air will cause the heater to burn.
It will not heat up after some time, as the heater will be burned.


Bertus

 

I would also replace the adjacent can capacitor. It may work with the existing one, but caps, especially electrolytics, deteriorate with age and lack of use. They can fail in spectacular ways.

 

A 5Y3 is still a common enough tube. Better to keep it as is to avoid the B+ arriving before the other tubes are warmed up. Still...

You could replace it with silicon diodes if the peak voltage doesn't get too high for the capacitor during warm up, and you would have to add resistors to keep the B+ voltage from being too high continuously. (I've done it.) IIRC, that one needs about 80 ohms in series with each silicon diode. Just in case the day comes when you can't buy a 5Y3.