517

The Tektronix 517 is a 50MHz scope introduced in 1950 or 1951. The power supply is an external box, like the 507, 551 and 555. The 517 does not take plug-ins. There is also a 517A. The 517 closely resembles a scope that Tektronix developed under a contract for the US military during 1949 and 1950. (See link below.)

Tektronix engineer Frank Hood recollects:

"A lot of progress was made in 1949 and 1950. Work was well underway by Logan Belleville, Dick Rhiger and Howard on the high speed scope, the 517. This used some brand new circuitry, distributed (or chain) amplifiers, using 16 to 20 tubes in each stage to get the power needed to handle the high frequencies. Our best prediction at that time was that there were only about 30 to 50 people in the whole world who had need of a scope with 60 to 100 megacycle bandwidth. As it turned out, when we brought out a higher speed scope, people were able to design equipment of greater bandwidth and needed even faster measuring instruments. The cycle was regenerative. Having faster, more accurate measuring tools created a demand for even more measuring tools. We eventually sold several thousand of this instrument."

The external power supply and oscilloscope are connected by a removable cable with a Jones plug on one end and a Jones socket on the other end. Units with serial numbers from 101 through 1739 use 12-pin Jones 2412 connectors; after that it is a 16-pin Jones connector. The voltages on the 12-pin connector are:

Pin 1: +750V, regulated
Pin 2: +475V, regulated
Pin 3: +350V, unregulated
Pin 4: +225V, regulated
Pin 5: +150V, regulated
Pin 6: Ground
Pin 7: -250V, regulated
Pin 8: +180V, unregulated

Later 517A units uses the same cable as the 551 and 555.

The 517 makes extensive use of the distributed amplifier concept. Originally the 5XP CRT was used, which has 38V/cm vertical deflection sensitivity when operated with 24kV acceleration voltage. Since the vertical sensitivity at the input connector is 0.1V/cm, we can calculate that the voltage gain from the input connector to the vertical deflection plates is 380. For 4cm deflection, a 152-volt differential output swing is required. There are DC blocking capacitors at various places in the signal path. The slowest sweep is 20 us/cm. The 517 is not designed for low-frequency use. The vertical signal path is as follows:

Gain Stage 1: single-ended, six sections, distributed, 6AK5 pentodes
Gain Stage 2: single-ended, six sections, distributed, 6AK5 pentodes
Gain Stage 3: single-ended, seven sections, distributed, 6AK5 pentodes
Trig Pickoff: one common-cathode 6CB6 pentode
Signal Delay: 51 feet of RG63U 125-ohm coaxial cable
Phase Splitter: single-ended in, differential out, three sections, distributed, 6CB6 pentode
Gain Stage 4: differential, six sections, distributed, 6CB6 pentodes
Gain Stage 5: differential, twelve sections, distributed, 6CB6 pentodes

There is a trigger amplifier in the 517 which can take its input from an external source, or from the trigger pickoff in the vertical pre-amp, or from the internal rate generator circuit. The trigger amplifier circuit has five stages:

Phase Splitter: 6J6 dual-triode connected as a differential amplifier
Gain Stage 1: single-ended, three sections, distributed, 6AK5 pentodes
Gain Stage 2: single-ended, three sections, distributed, 6AK5 pentodes
Gain Stage 3: single-ended, common-cathode, 6AG7 pentode
Gain Stage 4: single-ended, common-cathode, 6AG7 pentode

The 517 uses 24kV total acceleration voltage on the CRT. This is generated by the Type 420 High Voltage Power Supply subsystem in the 517. It uses a 1.8kHz oscillator to produce the high voltage, unlike other Tek scopes which use HV oscillators in the ultrasonic range.

The power consumption of a 517 is 1250 watts. The indicator unit weighs 76 pounds and the external power supply weighs 72 pounds.

517 units with serial numbers 101 through 925 use the DuMont 5XP CRT. Later units use a Tek-made CRT, the T517PxH/T54PxH, where "x" designates the phosphor type: 1, 2, 7, 11, or 16. The 5XP has three anode connections: 6.6kV, 13.3kV, and 20kV. The Tek-made CRT has just one anode connection, 20kV, and has 15 V/cm sensitivity at 24kV total acceleration voltage.

The 517 has a switch on the front panel that selects between normal vertical sensitivity, which uses the full 24kV acceleration voltage, and "X2" mode, which drops the acceleration voltage to 12kV for a doubling of the vertical sensitivity. The control works by switching the the voltage division ratio of the feedback to the error amplifier in the HV supply.

The 517 might be the only Tektronix instrument to have a part made of wood. There is a wood support for a large electrolytic capacitor, C826, which filters the probe power.

In 1965, following the introduction of the 50MHz 547, the 517 was discontinued. The 547 uses a non-distributed solid-state vertical amplifier, tunnel diode triggering, and a 6.5 V/cm CRT, thereby achieving good performance with lower cost, size, weight, complexity, and power consumption than the 517.

Comparison of 517A with 547
	517A	547 with 1A1
Bandwidth	50MHz	50MHz
Sensitivity	50 mV/cm	50 mV/cm
Cost in 1964	$3500	$2475
Size	scope + power supply	all in one
Weight	148 pounds	71 pounds
Complexity	130 tubes	45 tubes
Power Consumption	1250 watts	510 watts