lavoie: LA-265A, a superb Tek clone

The Lavoie LA-265A was a militarized version of the Tektronix 545A oscilloscope mainframe, of course capable of replacing even other mainframes, as the 531, the 535 and the 541. In the late fifties military asked some suppliers, Hickok, Jettinson and the same Lavoie Laboratories, for second sources of this family of widely used instruments. LA-265A was a true second source for the appreciated Tek mainframes. For this oscilloscope Lavoie also built at least four vertical plug-in amplifiers, the LA-265-D, the LA-265-CA, the LA-265-B and the LA-265-L, fully compatible with Tek D, CA, B and L types. Probably this line was introduced quite late, when the 545A was already a mature instrument, to prevent predictable reactions by Tektronix. We can date its production start up around the early sixties, since the first edition of the related technical manual, T.O. 33A1-13-229, is dated 1 November 1963.

Electrical and mechanical specs given in the manual are the same claimed for the model 545A. They can be summarized as follows:

 

 

The above figures are exactly the same given by Tektronix for its 545A oscilloscope, with the sole exception for power requirements: 500 VA for the 545A, even if with a different vertical plug inserted. Mistype or different test conditions?

Looking at the front panel of the LA-265A we find that the only barely appreciable differences are in the labels, silkscreened and not engraved, and in the control knobs, with few yet pronounced knurls in the Lavoie model.

Fig. 1 – Here are the front panel of a LA-265A and the panel of a Tek mainframe, a 585A in this case. Same controls and same layout.

Removing the cabinet side covers, the top class execution of the instrument can be appreciated. Golden-anodized aluminum is used throughout. Side covers are protected by a conductive mesh inside, over the vent slots, to prevent radiation interference.

Fig. 2 – Three views of the inside.

As in Tek scopes, passive components are mounted between rows of ceramic strips. In this case strips show variable spacing between notches, to accommodate components of different diameter. Another difference is the use of little metal tongues clamped to the ceramic strips, instead of metallized notches: this allows the use of standard soldering alloys, instead of the special silver loaded alloy used in Tek scopes. Quite remarkable differences are even in the sealed execution of the power transformer and of the fan motor.

Fig. 3 – Details of the time-base B, beside the power supply section, and of the sealed power transformer. The last picture on the right shows the HV stabilizer subassembly.

The most relevant departure from the solutions of the Tektronix 535A is in the CRT electron gun biasing circuit. Here Lavoie replaced the simple resistive voltage divider used by Tektronix with a voltage stabilization circuit, based upon a series of 31 NE-2 neon bulbs. These bulbs are potted with clear silicone compound inside a small aluminum can, its opening downward looking, and give a bright light all over the vertical amplifier section in normal operation. Details of this section are given in fig. 3c.

 

 

Fig. 4 – Schematic diagram of the original CRT H.V. supply. Each NE-2 in the B801 voltage stabilizer subassembly gives a typical voltage drop of 59 volts.

The above said overrefinement was eventually the source of the major drawback of this instrument. The voltage drop in the neon bulbs increases with their ageing, causing instability and fading of the trace brightness. The original circuit, showing the taps added to recover some ageing of neon bulbs, is given in fig. 4 above. In case of a probable failure of some neon bulbs, the simplest remedy today is to replace the entire subassembly either with suitable corona-discharge voltage stabilizers or with a series of zener diodes, as in the diagram below.

 

 

Fig. 5 - Here is the zener based circuit used to bring back to life the LA-265A in the pictures.

 

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You can find more information in Stan Griffiths' book on Tek scopes, and in this Antique Radio Forum discussion

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Dear Alan,

I just referred to technical aspects and not to legal affairs. In my life I appreciated tens of Tek vacuum tube oscilloscopes. My experiences start with the 535, the 545 and the 547 I used, and sometimes serviced too, at the Electronic Department of Polytechnic here in Naples around 1970 and still continue today with several oscilloscopes that I am restoring through the years. I was aware of the legal suit involving Tektronix against the United States and other firms for patent infringements. I also read of the final decision in favor of Tek in June 1971, when Lavoie had already gone bankrupt. Tektronix was well worthy of admiration because of its refined solutions, its top engineering and its unsurpassed performances. But despite the cleverness of its defenders in the legal suit, I have no interest at all in disputes about the effective validity of the Tek patents over US Government, that had certainly financed all the wartime research.

High-speed oscillography was already used in many military applications during WWII, to perform accurate measurements of distances. The so called synchroscopes, as the TS-28/UPN, were supplied as standard test equipment with each radar set deployed during the war. Examples of high-speed oscillography and associated CRTs can be found in volumes of the MIT Radiation Laboratory Series, but even Great Britain developed techniques and CRTs capable of operation at several gigahertz. If for instance we refer to very special circuits, as the wide band distributed amplifier used in these equipment, it was already known well before WWII. And DuMont itself in the fifties designed a lot of high-speed distributed amplifiers up to the gigahertz region.

Then the dispute on patent infringements seems the conclusion of an already written story, just to grant military with second sources for strategic instrumentation and to give Tek a compensation for the lost business. We must remember that at the date of the dispute Tek had already switched to higher performance mainframes, probably even to the the same 7K family mainframes and probably had discontinued at all its old 531 to 545 productions.

No doubt that the LA-265A was a clone of the 545, but this consideration alone should lead to an appreciation for the said instrument, with its own distinctive characteristics either in circuitry and in component selection.

As far as I know all the faults reported for this instrument refers to progressive dimming and loss of trace brightness. Despite of some wrong remedies, as the useless replacement of the HV transformer, faults are all referable to the very poor reliability of the B801 subassembly, used to stabilize the CRT electron gun biasing. Here the proper operation is impaired by drifts and faults of any of the 31 neon bulbs all series connected. The operator and service manual lists the procedure to recover small drifts in the voltage drop of the bulbs by moving the brightness-range selection jumper to different taps, illustrated in the figure below.

Of course the true problem arises from non-recoverable openings of single bulbs at the end of their useful life that prevents the operation of the whole CRT biasing circuit. I have no data about reliability and useful life of NE-2 bulbs. Nevertheless I would be very surprised to read of a life prediction in excess of very few hundreds hours for B801. Anyway this problem can easily be fixed replacing B801 either with a resistive voltage divider, as in Tek scopes, or with other network of voltage stabilizing devices, as in the above article.

With the sole exception of the said circuit, other sections of this instrument appears to be copies of circuits used in the 545A. Quality of components is the same or even better than those used by Tektronix, as evidenced by the use of the hermetic power transformer. Custom made parts, as coils and delay lines, look very well done. I never was in the payroll of either Tektronix or Lavoie. Nothing against Tektronix, but please give me one valid reason why this instrument cannot be considered at top levels, as its quality and performances deserve? In my opinion even the same fact that someone succeeded to make a good copy of such a complex instrument is anyway a great result.

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Dean Huster spent his Navy career in electronics repair and calibration and is certainly qualified to hold an opinion of the workmanship and reliability of the LaVoie clones: he saw several of them when they were relatively new, and had to certify that they met their specifications.

 

Regarding patent policy, you surely aren't saying that there have been no advances in oscilloscope design since WW2.  If Tektronix spent money on research and development, and obtained patents in the process, presumably they were valid, and the company had every right to recover their r&d investment.  The US military had a long history of ignoring patents, and it took a company like Tektronix to stand up to them and finally put an end to that process.  

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Dear Alan,

Sorry if I am not able to properly transmit my thoughts, due to my poor English. Of course I do not want to diminish the fantastic research work at Tektronix. Anyway you should agree that Lavoie, as well as Hickok and Jettinson, developed their clones not as individual ventures but according to contracts coming somewhere from US Government. Military that ordered these equipment could not ignore the existence of Tektronix patents, unless they considered that patents either the result of previous contracts, and then already paid, or referred to already known solutions. In other words, the dispute itself generates doubts on the validity of some Tek patents, and I am talking of patents not of products. At last, we know, US Government lost the legal suit.

No doubt anyway that LA-265A was a copy of the 545A, requested and authorized by military. No doubt of its top quality, with the sole exception of a wrong solution in the CRT gun biasing circuit.

Regards, Emilio

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The military ignored all patents, valid or not. Up to that time, no company would challenge that policy, because of the heavy legal costs, and because of jeopardizing any future military contracts.  

 

Even though Tektronix lost money overall on this lawsuit, Howard Vollum presumably carried it through on principle.  There aren't many companies run by executives with principles, and I admire him for it. The fact that Tektronix eventually won the suit shows that he was correct.  The military had no legal authority to take property (patents) without compensation.

 

By the way, the third company was Jetronics.

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Dear Alan,

many thanks for your clarification above. Since the end of WWII military market was vital for many companies. Of course Tektronix was less dependent from military than other firms, selling its oscilloscopes virtually in countless market segments, even to the same military contractors as Lavoie, Hickok and, right, Jetronics. What you say confirms that Tektronix brought the dispute in order to assert a principle from its position of relative strenght or, in other words, indipendence from military. Nevertheless it is hard to believe to piracy actions by US Government: certainly even military had their own reasons if the matter went to a conclusion before a justice court.

But this leads us off from main topic. My thought is that Lavoie engineered its version of 545 in direct response to a Government contract and therefore its liability in patent infringements was at least questionable. And this should not influence technical evaluations of the LA-265A.

Regards, Emilio

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