Tektronix 535A and 545A
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:
Some ripple is still evident however the rise overshoot has gone.
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“Type 545 was introduced February 7th, 1955 along with the Type 541, and superseded in 1959 by the Type 545A, which was in turn superseded in 1964 by the Type 545B.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:
Here is the 545A distributed Y amplifier:
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:
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:
Here is a picture showing the entire Y amp side of the 535A over the 545A:
Since the timebases are nearly identical, I have not provided a picture here, if you want to see more go here.