Tektronix 535A



Test Equipment Index


Manufacturer Tektronix
Model 535A
Age Early1960's?
Service Data Yes, PDF copy of handbook.
Condition Good - partly working (now about 95% - see below)
Comments One of the famous Tektronix 500 series scopes, the 535A is a dual timebase 15MHz scope, which will accept the letter and "1" series plug-ins. The scope is valve based, with a few semiconductor diodes, there are about 60 valves in the scope, mounted at all angles! I have managed to get most of this scope working, but have had a lot of switch trouble, with poor insulation on the wafers - this seems to be due to contamination with oil, and they have so far responded to thorough cleaning. The top picture shows the scope with a TU7 test unit installed and working.

UPDATE. I've now managed to get the scope working at about 95%. I still have to calibrate the timebases, and fix a fault with the B timebase trigger circuit - for some reason, I cannot balance the trigger circuit. A number of faults were cleared by replacing an open-circuit resistor in the horizontal shift circuit. As the horizontal amplifier is DC coupled, a DC offset on the input manifested itself as an apparently fast running timebase (the give away is that both timebases exhibit the same symptoms).

The plug-ins allow the scope to perform a variety of functions, with single and multipletrace units, differential input, component testing, transducer monitoring, and spectrum analysis among the options. I have a number of different units (including CA, K, L, D, E, TU7, 1A1, 1S1 and 1L5), which I am slowly repairing.

It is rumoured that you can display a television ptcture on one of these 'scopes - has anyone seen it done? I suspect that it will need an external synch seperator, and will certainly need a video amplifier, as the 'scope requires an input of about 20V to 30V to un-blank the CRT. I will try and verify this story! See here for how it's done.

UPDATE 2. The 535A is now working as originally intended (well nearly - I'm not totally happy with the B timebase trigger circuit, I think it really needs a specially selected valve (ECC88), not just one from the junkbox), otherwise, the unit has been re-calibrated and repaired. It has required about 6 new valves, three resistors and a capacitor - not bad for such an old and complex instrument! Now I have to work on some of the plug-ins.

Off screen picture of square wave from TU7 test unit. The scope gives a very bright crisp trace, though with a limited size of graticule.

Left side view, showing tube at top, Y amplifier bottom left, and plug-in bottom right. The "L" shaped unit with the holes, going up the left side and across the top is the delay line, to allow viewing of the leading edge of the triggering pulse.

Right side view, with power supply at the bottom, "B" timebase folded out, and "A" timebase and EHT generator along the top.

Showing the 535A on a purpose built trolley (not Tek), which has space for two plug-ins under the main stand (type L in one compartment), the top of the trolley tilts to adjust the viewing angle. There are a "CA" and "1A1" plug-ins on the bottom shelf.

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Copyright J.Beacon & M.Wroe-Parker 2004