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Tektronix 535A and 545A

April 21, 2013

Tek 545A & 535A 1MHz Square Wave at 100nS:Div
The 10MHz 535 was introduced in 1954 with the brown box cabinet, updated in 1956 to the blue clam shell cabinet. In 1959, type 535A was introduced having better controls and a 15MHz vertical amplifier versus the 11MHz 535. The A timebase provided 24 settings, the speed range being 5S/cm to 100nS/cm while the B timebase had 18 settings, 1S/cm to 2µS/cm. The timebase ranges of type 545A are the same as those for type 535A. On both models, a 5X multiplier was provided to increase the maximum speed of the A timebase to 20nS/cm, quite fast.

The picture above shows the 545A on the left fitted with a 1A1 50MHz dual trace plug in and the 535A on the right, fitted with a 1A2 50MHz dual trace plug in.
The maximum sensitivity of the 1A1 is 5mV/cm, the bandwidth at that sensitivity being limited to 28MHz while that of the 1A2 is 50mV/cm, Both units could provide the full 50MHz at 50mV/cm. The scopes are showing a 1MHz squarewave from the fast rise output of a type 106 squarewave generator displayed at 100nS/cm, the overshoot and ripple that I thought was due to delay line issues is actually mostly due to termination issues resulting from trying to drive both scopes at once. Thanks to Bruce Baur for pointing this out. Below shows each scope set up the same but driven separately, Type 535A:
Tek 535A Fast Rise Square at 100nS:S
Some ripple is still evident however the rise overshoot has gone.
Type 545A:
Tek 454A Fast Rise Square at 100nS:S
A very clean trace.
Fairly soon after the 535 was introduced, the demand for greater bandwidth brought the 30MHz 545 and quoting directly from 545-TekWiki:
“Type 545 was introduced February 7th, 1955 along with the Type 541, and superseded in 1959 by the Type 545A, which was in turn superseded in 1964 by the Type 545B. The difference between the 545A and 545 is the control ergonomics, not any major circuit design changes.

Types 545 and 545A have a six stage differential distributed vertical amplifier made of twelve 6DK6 tubes. The vertical amplifier used in the 545A is also used in the 551 and 555. The 545 uses the 154-098 CRT. With the limited CRT technology available at the time, the higher bandwidth of the 541 and 545 came with a tradeoff. The vertical scale is only 4 divisions, 2 above and 2 below the graticule center line. The lower bandwidth 531 and 535 retained the 6 vertical divisions, as used in most other Tektronix scopes.”
This is the 535A Y amplifier:
Tek 535A Y Amp
Here is the 545A distributed Y amplifier:
Tek 545A Distributed Y Amp
All these tubes result in a tube count of 74 plus the CRT, with a CA dual channel plug in this would result in a 90 tube room heater!
Here is the distributed Y amplifier schematic:
Tektronix 545A Distributed Amplifier
The distributed amplifier tubes, V1104 thru V1214 are type 6DK6 while the driver tubes, V1033 and V1043 are type 6DJ8.
(Rant mode on: Audiophiles are known to destroy Tektronix scopes for the 6DJ8s, usually to use in frankly lousy circuits. I hope what I am doing helps to generate awareness of and respect for these ground breaking instruments. However, in these crass times, people seem to think that ownership equates to the right to do what they like rather than something more mature like stewardship. Rant mode off.)
The circuit description in the manual says this of the distributed amplifier:
“The output stage is a 6-section distributed amplifier. The tapped inductors in the transmission line between each grid and each plate, isolate each section from the capacitance of the adjacent sections.
The input signal for each tube is obtained from the grid line which is driven by the cathode followers V1033 and V1043. The amplified signal at each plate, fed to the plate line, becomes an integral part of the wave traveling down the line toward the deflection plates.”
And here it is displaying a 30MHz sine wave at 20nS/cm:
Tektronix 545A 30MHz
Here is a picture showing the entire Y amp side of the 535A over the 545A:
Tek 535A over Tek 545A
Since the timebases are nearly identical, I have not provided a picture here, if you want to see more go here.

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15 Comments
  1. Lars permalink

    Something special at every piece. There is no doubt that these machines build Tektronix reputatation as a “solid” company.
    My Tek 549 and 214 are now part of the Stuttgart University Computer Museum:
    http://computermuseum.informatik.uni-stuttgart.de/
    They will assist in reparing equipment of the same age. A very useful place for a vintage scope, I think 🙂

  2. Bruce Baur permalink

    Richard, I don’t think the aberations are from the delay line. Once adjusted they almost never need attention unless someone wanted to tweek them up, then they are hell to get back to good operation, tweek, tweek and retweek. I would check termination and the generator.

  3. Hi Bruce.
    Thank you for this input. Yes, it was a termination issue and I have revised the text and added new pictures.

  4. I was planning to get one from a local seller and while searching for Tektronix 535A techical manual, which lead me to this page.

    I must say you did a wonderful job in restoring this legendary piece of equipment. They are really beautiful to look at.

  5. Joy Fulleman permalink

    I have a Tektronix 545 Oscilloscope. Some questions: When unit is powered off and unplugged, are there any areas in the unit that would still be charged or can I touch anything inside w/o danger. Also, how could I at least partially test the unit? It has powered on, fan runs, tubes light up, etc. Thanks!

    • Hi. Sorry I have taken so long to reply. You don’t say if it is an A or B model. I am only familiar with the A model.
      First if you open it, leave it 30 mins after powering down and pull the power cord. The only possible place a charge will remain is on the tube PDA anode (under the rubber cap near the screen). Having said that, I have never had a shock off this anode.
      If you want it to work without too much temperament, deoxit ALL the tube pins and sockets. Also all the switch contacts. This applies to the plug in also. If you don’t do this all may be well, but it is unlikely and will then be frustrating!
      Power Off.
      Set the calibrator to 2V. Set the focus off to one end, this is to avoid the possibility of burning the screen. Set the intensity all the way up (full CW).
      Set the A trigger mode switch to auto and the source to INT either + or – , doesn’t matter, this should free run the time base. Set the A sweep rate to 1mS/cm and the display to A. Set the horizontal and vertical positions to the middle of their travel. If it is a dual channel plug in set to channel A and set the sensitivity to 1v/cm.
      Now power it up and a blurred trace should appear somewhat near the center of the screen. Turn the intensity down and focus it, keeping the intensity as low as you can and still be able to see the trace clearly. Now, run a lead from the cal out to the A channel in. A 2cm high squarewave should appear, and it should be stable. If this happens, now you can set the A trigger mode to AC and the stability to preset, fiddling with the level control around center should cause the timebase to trigger. If this is the case, removing the signal should cause the trace to disappear. If you have sinewave generator, now connect this and get the waveform to display. Playing with the level control should cause the sinewave to move left and right as the voltage level (not amplitude, level) at which the timebase triggers changes. It is designed to be able to cause the timebase to trigger repeatedly and precisely at a set DC voltage positive or negative relative to zero (trace centered on the screen).
      Now it is up to you to figure out the rest: Sometimes the little operators booklets that line in the hatch on the top appear on ebay, if one does, BUY IT!
      There are tutorials on triggered oscilloscopes on the net. Once you get that down, you can start to investigate the use of timebase B to delay timebase A.

  6. Sorry, can’t help, am liquidating my collection!

  7. I’m trying to find the date of manufacture for my 535A by serial #. Thanks

    • I can’t help but maybe one of the folks at the Vintage Tek museum can. You will find a link on my links page.

  8. After giving my 535 away to the Computermuseum in Stuttgart, I’m receiving a new one with a frequency analysis plug-in end of this year (from a lab closure).

  9. if anyone needws help or parts forr the 535/545/585 scopes aqnd plugins I can help,call me at 518-752-5206,best regards joe oneill kb2ttje

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