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Hickok 1805A

March 13, 2014

I took this one in order to get a scope-mobile which are hard to acquire since people understandably don’t want to ship them. The original model label had been removed (perhaps in shame), note the replacement label above the CRT, it sets the context for this post!
Hickok 1805A SN 00426 New Label
The US government issued a bid request for oscilloscopes based on the Tektronix 535 and 545 as a result of (as I understand things) a complaint from industry that Tektronix had monopolised the market. Well of course they had, their instruments were at the time, the standard bearer for oscilloscope function and quality! As a result, Hickok, Lavoie Labs and Jetronix Industries produced a large number of instruments that were blatant copies of the Tektronix instruments. It is said that imitation is the best form of flattery but these were pale copies based on what I have read and my experience of the subject Hickok 1805A. I note that not many of these copies seem to have survived, perhaps proportionally more went to the landfill than did Tektronix units, who knows?
Anyway, here it is working and in calibration after about a month on my bench. It was quite a trial, considerably more resistant to my ministrations than the genuine machines. It is now working properly and in calibration, here it is displaying a 1 mS marker and the calibrator waveform:
Hickok 1805A SN 00426
I read a comment regarding the Hickok 1805A on one of the forums where the author said that he thought it was subsequently produced under the Tektronix brand! That is putting the cart before the horse to put it mildly; I find it surprising that anyone who is interested in vintage electronic instruments would be unaware of the ground that Howard Vollum and his company broke. And this is not a myth, Tektronix really did develop and produce the first high-performance, reliable, triggered oscilloscope available.

This 545A copy has the Hickok 1823 Plug-In which is a copy of the Tektronix type 53/54C dual channel model which has a bandwidth of DC to 24 MHz and sensitivity from 50 mV/cm to 50 V/cm. Operating modes are A, B, A & B chopped and A & B alternate. (The later Tek type CA was the same but with the addition of A+B and A-B modes which I find to be very useful. Incidentally, the ability to sum and subtract the two channels is a major advantage of a two channel beam switch scope over a two beam scope.) Here are pictures of the 1823:
Hickok 1823 CA Copy a
Hickok 1823 CA Copy b

The primary patent issues were the ground breaking sweep circuit (due to Dick Ropietquet) and the distributed wide-band vertical deflection amplifier. Hickok did not contest the two issues arising from the distributed vertical amplifier patents and so the litigation focussed on six issues arising from the horizontal circuits.
Tektronix filed suit in February 1961 and the action was not settled (in their favour) until May, 1970, the final award not being settled until early 1979 at just over $4 million. This suit set a precedent whereby the US government could not longer flangrantly disregard patent ownership and that is most likely why it took so long to settle.
Here is the rather neat summary of the Tektronix horizontal circuits in question (sweep generator), cited in the litigation proceedings:
“Generally and somewhat oversimplified, the horizontal circuits in question have four components: a sweep generator, a multivibrator, a signal trigger, and a delay (or hold-off) system. The sweep generator is the heart of the circuit. Its function is to generate a linearly rising voltage which, applied to deflection plates in the cathode-ray tube, sweeps the electron beam horizontally across the tube. The multivibrator controls the sweep generator. In effect, it turns the sweep generator on and off by supplying to it one or the other of two control voltages. The signal trigger supplies to the multivibrator a pulse, by which the multivibrator is actuated. The delay or hold-off system serves to prevent the multivibrator from being triggered out of time by an incoming signal pulse and, particularly, until the conclusion of a sweep cycle.”
You may read (if you have the stamina) chapter and verse on the technical issues at

I am not going to post a lot of pictures this time, it is sufficiently similar to the 545A I posted on previously, just not as well put together. To give you some idea of what was involved, here are before and after pictures of the HV supply:
Hickok 1805A HV PSU Before
Hickok 1805A HV PSU After

I soon discovered that it would not work properly when a dual channel plug-in was set to the Alternate mode. In this mode, the timebase sends a negative pulse at the end of each sweep to change the state of the channel switch multi, thereby turning the Y channel just displayed off and turning the alternate channel on and so on. This signal originates as a positive going pulse at the screen grid of the second stage (right hand side if you will) of the timebase gate multi (which reverts to the positive state to end the sweep) which is amplified and inverted. I fooled around with this for a long time, on and off. The pulse seemed ok but in fact was of excessive amplitude and poor shape. It finally (in the way of these things) sank in that the screen grid choke may be open. The SG was still energised via the core resistor. Well, the choke was open so the SG signal was developed across the core resistor hence the poor shape and excessive amplitude. So, I got to glaring at the outside of this choke using a magnifying glass and despite absolutely no signs of abrasion or impact, spotted one end of the break. (Such breaks usually occur on the outer layer, fortunately.) After much further glaring, having located one end, I found the other and was able to tease each end out from the criss-cross winding sufficiently to be able to tin the ends and place a single strand of wire to bridge the break. It worked and Alternate action was now available. I placed a little varnish over the repair to fix it in place. I seem to be developing some expertise in repairing broken thin-as-a-hair choke and transformer windings! It comes with the territory I guess.
Hickok 1805A Gate Screen Choke Repair
Oh, and I made a copy of the Tektronix 535A/545A operators booklet that should live in the little compartment on the top:545A Operators Booklet


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  1. Keith permalink

    Richard, I remember when I went through my Air Force Precision Measurement Equipment school in 1972-73 that my instructor relayed the story of how the Air Force contracted with Hickok to build these Tek 545 clones… and in fact gave Hickok all the pertinent technical data to do so. I might add that Tektronix was not the only victim. The Air Force also had Hickok build clones of the Hewlett Packard 410B Vacuum Tube Multimeter.

    • Hi Keith.
      I was aware of other instances of government sponsored plagiarism but not in detail. Tek were the first to sue, others were unwilling to do so because they were heavily dependent on government contracts. Tek was commercially successful (with good reason) and were not dependent on the governent for survival and so they sued. Other manufacturers were so concerned by Teks action that they tried to get Tek (Howard Vollum really) to desist. However, the Tek enterprise had real integrity and they prevailed, in the end.

  2. Keith permalink

    Richard, I believe I read somewhere that the Lavoie “545 knockoff” was made under the same sort of arrangement as the Hickok one. Do you know anything about the Lavoie history? I do remember something about the Hickok scopes that may be off interest to you. The technical manuals were copies of the Tektronix manuals. However, the original Tektronix schematics had light blue lines partitioning off parts of the circuits. When the manuals were reproduced by the military and provided to Hickok, this light blue lines came out as black lines and were misinterpreted as circuit runs. In my tech school we were made very aware of that inaccuracy so that we didn’t make the same mistake.

    • Hi Keith.
      I didn’t know about the line colour issue however, the Hickok manual is very thin on the circuit description and operation, presumably to avoid admitting the extent to which the design was plagiarized.
      My notes do mention the three main pratagonists, Hickok, Lavoie and Jetronix. There is also a link to the case law in the narrative that addresses the technical details of how each defendant attempted to justify their case.

  3. Kevin Kennedy permalink

    Very interesting story – I had heard a little about the plagiarism issue early in my career just after the lawsuit was settled. I’ve never seen a Hickok 1805A and did not know they existed until your article. I had a 545A for 20yrs and only got rid of it because its size and heat output were incompatible with my then new basement lab and listening room space. I got another Tek of course!

  4. Dave Wise permalink

    Richard, your photo of the Hickok high-voltage compartment is very interesting. The transformer – sourced from Industrial Transformer Corp. – is completely different from Tek’s. It’s enormous! Is it still about 50kHz like the Tek?

    • Hi David. I don’t recall the precise frequency however yes, in the 50kC range.
      It is actually not much bigger than the Tek transformer, I imagine that the actual transformer inside the can is very similar.

  5. Tom Phillips permalink

    I have a Hickok 1805 from my father-in-law’s estate. I would like to know the year these were made. My plan is to donate it to our local museum.

    • Hi Tom.
      Donating it is a great idea. I am not sure about the dates, likely in the late 50s to the mid 60s, probably longer. If you scan down my notes, you will find a link to the patent suit opinion, there may well be dates there, I can’t remember.

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