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Heathkit IO-14

June 28, 2011

Heathkit described this as a laboratory scope. It is quite nicely made, at the top end of amateur quality and appropriate for a high-end kit. It does have regulated power supplies and triggered sweep but no calibrator. Compactrons are used in the regulators but you would not know, it is huge (and heavy) for its limited performance. It is heavily modelled on Tektronix including the CRT bezel, the boxes on the front panel that group the control functions and the power supply topology. While capable of making measurements, it is not a true laboratory scope however, it was well suited for serious amateurs, college learning labs and now, historical interest.

The basic specifications are:

Y; -3 dB at 8MHz, rise time 40nS, sensitivity, 50 mv/cm to 20 v/cm.

X; 0.5 S/cm to 200 nS/cm.

Heathkit saw fit to equip this beast with delay lines; it is not possible to completely eliminate the bumps and ripples that are characteristic of an unmatched delay line. The manual admits this. Speaking of which, why does this thing have delay lines, other than to sell it? Given that the time base maxes out at 0.2μS/cm and that above 2MHz, the triggering is useless, there will be no examining fast edges with this one, so the delay lines seem to be cosmetic. If you can enlighten me, please do so and I will update this post. This is the best I managed to capture the delay line settling aberrations. The display is actually much more clear than this photograph. The square wave source is a Tektronix 106 at 100kHz from the fast output.

An interesting feature is the DC coupled unblanking solution: To sumarise, Tektronix used separate CRT grid and cathode supplies with the ground end of the grid supply strapped to the unblanking cathode follower, Solartron and Dumont used a bistable riding on the CRT grid or cathode. Here, Heathkit have used a 1750 volt gas tube (Victoreen HV-173) to bridge the potential difference between the unblanking cathode follower and the CRT grid, I like this a lot, very simple and effective. Having said that, there is an issue; the gas tube maintains a fixed voltage between the unblanking cathode follower and the CRT grid so if the high voltage is not set perfectly, either there will be no trace or there will be a trace and the intensity control will not work.

In fairness, I imagine it sold for a lot less than anything comparable and did offer an amateur a presumably affordable, decently accurate scope, capable of making measurements, not just looking at waveforms; anything else I am aware of including other contemporary Heathkit offerings, would not be capable of making measurements. So, that is the context for this scope and a good reason to have it in this collection.
These days, we (I) am spoilt by the affordable availability of equipment that in its day would have been beyond the means of an amateur.

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17 Comments
  1. Henry Hopkinson permalink

    Hello Richard
    I bought one on E-bay not knowing that the sweep would not work above 2.5Mhz.I did not find out until I bought a manual and boy was I angry. I still have a complete assembly manual along with a large schematic. I have since taken it apart because it did not work when I got it, you know “being sold as is”. If you are in need of patrs let me know.
    Henry

    • Hi Henry.
      Yes, the IO-14 is a disappointing beast. It is actually capable of work up to 8 MHz but the triggering does not support that solidly. Sometime, I will take a look at sharpening up the trigger response, the topology is “normal” and it is a matter of circuit values and maybe a RF plate choke in a strategic location.
      Thanks for the offer of parts.
      Richard

      • Henry Hopkinson permalink

        Hi Richard
        Thanks for the responce.There is a Heathkit IO-14 on E-bay as we speak. The seller wants $100.00 for it plus $72.00 to ship it from California. I am thinking of offering $25.00 since it does not work. He pluged it in and it did not power up. What is your opion on buying it.
        Henry

      • Hi Henry.
        I really don’t rate this machine for any usage. In my collection, it has a perspective and that is it. That he plugged it in and it did not operate tells us that there is a problem, it is unlikely (though possible) that somebody simply removed the fuse. I would rather work with a dead Tek or HP. If you want a good 10MHz valved scope, keep an eye out for a Tek 316. Even then, as you have read, it will need some attention. Dried out electrolytics can kill the power transformer while leaky POI caps will cause malfunction. That is what there is to deal with in these old pieces of kit.
        Richard

  2. Rick permalink

    Wow!

    What can I say. This sure brings back memories.
    I used one of these for about 10 years in servicing Hi-Fi equipment. I put cheesecloth on the louvers to filter the incoming air and prevent dust buildup inside.
    This was quite a workhorse, it powered on and off each weekday with the breaker for about 10 years without fail. Definitely not the highest performing scope I ever sat with, but rock solid in my opinion.

    Rickey.

  3. Jim Hauser permalink

    Hi Richard,

    I bought one back in 1969 and carried it on the road with me when I worked for Unimate. I bought
    it for its bright trace and 10ns rise time which when I checked it out on was 8ns. I just bought
    another one on E bay that appears to have all of the power supplies and CRT functioning. I hope
    it survives the FedEx wrecking crew.

    Jim

    • Hi Jim.
      It is good to know that you will be saving another one and that you like it. As for Fedex, I have been extraordinarily lucky with no damage sustained in receiving many, many pieces of tube kit.
      Richard

      • Jim Hauser permalink

        Hi Richard,

        I am glad to hear that someone is having better luck with FedEx than I am. I worked for Heathkit for 4 years ,1970-1975, as a Sr. Tech. The purpose of the delay line was to allow you to see the
        leading edge of a pulse that was too large or long to fit 2 repetitions of on the CRT. With the “brightness” set to the point that you lose control of the focus it worked very well for a $259 kit scope in 1968. I found a picture of the Lectrotech TO-50 and it does not look like the IO-14 at all. Tektronix had a line of low end test equipment and I think it was modeled after one of these
        scopes but I do not remember the brand name.

        Jim

      • Have you read any of my other posts? There is a hell of a lot of information on not only oscilloscopes of the 50s era but also the development of the time-base technology.
        I did just look up the Lectrotech TO-50 and on looking again, I have to agree with you. I will edit my text.
        Richard

    • I have just checked in the manual and the claimed rise-time is 40nS not 10nS.
      The “low-end” Tektronix line was actually a British company, Telequipment and this scope is most definitely not modeled after anything Telequipment made. As I said, the power supply topology is modeled on the Tektronix system of stacked series-regulators with a very accurate negative reference regulator. The time-base also, follows the Tektronix (Dick Ropietquet) topology, it simply does not work as well. I spent a lot of time bringing this beast back into specification and the resulting performance is merely adequate. That it was around 1/5 the price of anything Tektronix made completes the story, a lot of of scope for the money. Nowadays, top of the range tubed scopes are available for very little money and that is why I do not recommend this model.

  4. whelanjh permalink

    Many thanks for posting this material on the IO-14 oscilloscope. I built this Heathkit oscilloscope in 1968 at age 20 while in the Air Force. It served my hobby needs for 16 years with no failures. I finally replaced it 1984 with a Tektronix 2215.

  5. Bob Macklin permalink

    The Heathkit IO-14 is actually a Tektronics 561 knockoff.

    This was the best 5 inch scope Hethkit made. This scope is still very useable. Maybe as high as about 15MHz.

    I was using Tek at work in the late 60’s. In 1971 I bought an IO-14 to use at home. I used it at home until 1989. In 2000 when moving I dumped it I did not know about eBay yet.

    I just recently bought on on eBay for $35 and it is in decent working order. It a soon to be done restoration job. Mostly just sticky controls.

    Bob Macklin
    Seattle, Wa

    • Bob, the IO-14 is not a 561 knock off. Apart from anythings else, the 561 is an indicator (main-frame) that uses plug-ins for the X and Y axes.

  6. Alan McRae permalink

    Just dug out my Dad’s old IO-14 from a dusty corner of his basement. I vacuumed the dust out and it powered right up! Since I just got a used Radio Shack 300 in One Electronic Project Lab from Salvation Army and got it working, I’d love to look at circuit signals with this scope and learn a little something. Is there a user manual for this durable old beast that explains how to use it properly? If so, where can I get it? (PDF format would be fine by me)

    • Hi Alan.
      I don’t have an operators manual. If you look online you should be able to find a tutorial for a basic triggered oscilloscope.
      Essentially, the Y axis has variable sensitivity in terms of voltage to deflect the trace a cm vertically.
      The X axis has a triggered sweep that can be varied in rate in terms of time/cm horizontally, this is known as a timebase. The timebase may be triggered in which case a steady signal in necessary to keep it running. To watch varying signals like speach, set it in auto (free run) mode, then the sweep will be present without a signal.
      Be careful to keep the brightness or intensity only as high as needed to avoid burning the screen. This is critical if just a spot or baseline is present.
      If you have a microphone, play some music and play with it!
      You can find a signal gen app for your smart phone, get a jack to RCA cable and a RCA to whatever is on the scope Y input (radio shack) and play, you should soon see the relationship between frequency and timebase sweep rate. For example, a 1kHz signal has a period of 1mS so at 1mS/cm you should see 1 complete cycle per cm or 10 cycles across the graticule.
      Enjoy!
      Richard

  7. HI everyone I some time use a tektronix 545a for the odd measurement just to keep her running huge thing 89 tubes in it or tek 564 storage scope both been restored by me over the last two years. well made. other than these two I use a hameg 705 only do audio repaires so suits me fine. lives in uk

    • Hi David. Thanks for sharing. I was brought up in Farnborough, Hants in the days when there still was a R.A.E!
      I have some audio stuff at richardsears1/wordpress.com

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