310

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The Tektronix 310 is a compact portable oscilloscope introduced in 1955. It is a 4 MHz single-trace, single-timebase scope with a 3" (7.5 cm) round CRT.

The Hickok company produced a clone of the 310 under a US military contract as the AN/USM89B.

Specifications

Bandwidth 4 MHz (3.5 MHz below 0.1 V/Div, AC coupled)
Rise time 90 ns (100 ns below 0.1 V/Div, AC coupled)
sweep 0.5 μs/Div to 0.2 s/Div 1-2-5 sequence
Deflection 10 mV/Div to 50 V/Div, 1-2-5 sequence (below 0.1 V/Div only AC coupled)
Input impedance 1 MΩ // 40 pF
X input 1.5 V/Div, 500 kHz, 100 kΩ
Z input 20 Vp-p at rear "CRT Cathode" binding post
Calibrator 0.5 Vp-p to 100 Vp-p, 1-2-5 sequence; 1 kHz
Power 175 W

Internals

Cooling

The 310 is a tube scope and uses 175 watts, but it does not have a fan. Therefore, it tends to run hot, particularly when used in a hot environment with still air. It has a 165 °F (74 °C) thermal cutoff switch in series with the primary of the power transformer. For extended use in one place, a tilted fan base, the FB310 (part number 016-012) was available. The fan base blows air upward through the perforated bottom panel of the 310.

The 310 is hinged at the rear, allowing reasonably convenient access to the circuitry despite the fact that the components are packed more densely than in other Tektronix scopes of the era.

310A

There is also a revised version, the 310A, introduced in 1959. The 310 uses printed-circuit boards but the 310A returned to ceramic strip construction. P2 phosphor was standard. P1, P7 and P11 were also available.

Is this the only time that a Tek design was moved from PCB back to ceramic strip?

This is a nearly true pure vacuum-tube scope, but in the power supply there are some silicon rectifiers and in the circuit is one germanium point contact diode. It is sometimes very useful because it contains a 1 kHz calibrator output with up to 100V level combined with a step attenuator.

Early examples of the Tektronix Type 310A used commodity 3WPx CRTs. At some point in production, they switched to a Tek-made CRT, part number 154-366, which is compatible with the 3WP2.

Unlike later Tek instruments, where the incremental model designated by an “A” suffix only occurred with a significant specification or performance enhancement, the original 310 and 310A were essentially identical. They even shared the same manual and schematics. The main difference was the wiring construction.

The original 310 pioneered the use of circuit board construction, rather than the trusted ceramic strip point to point wiring. The circuit boards were two sided, however plated through hole technology to interconnect the layers had not been invented yet. Rather, all of the holes for component mounting and interconnect contained a rivet which was expanded in a press before the components were installed in the board. The rivets themselves were not soldered to the copper foil traces, and relied on the pressure from the crimp to make contact. This proved to be extremely unreliable, with many intermittent connections resulting in high warranty- and after-warranty failure.

The 310A model essentially used the identical circuit design, but returned to the trusted ceramic strip construction method.

The 310A also replaced the selenium plate rectifiers in the power supply with silicon diodes. Tek offered a retrofit kit, to be installed in the service centers, to upgrade older scopes with selenium rectifiers.

During the lifespan of the 310, Tek evolved its color scheme. The original 310 scopes had a case painted with a blue metallic hammer tone color. Later units moved to the crinkled “Tek Blue” color still in use today.

The scope cabinet was hinged to allow it to be opened like a book and operated for access to the circuitry for service purposes. The 310 and 310A were convection cooled, and required free access to air through the cabinet vent holes to avoid overheating. It contained a thermal cut-out to protect it from damage if the supply of cooling air was inadequate. The scope has feet on the rear panel to allow it to be operated on the floor with the front panel facing up, but the manual warns against prolonged operation in this orientation. Shortly after introduction, Tek offered a Fan Base accessory, which the scope would sit on and provide forced air for better cooling. While the scope had universal primary wiring options, the fan base did not. Separate models were available for 115 VAC or 230 VAC operation.

Like most old Tektronix devices the mains transformer holds an indefinite(!) warranty, so hold an eye to that. The device goes away on ebay here often for 30€ to 60€.

Fun on

  • But its not quite clear what the "indefinite" means, live long for the device, the first owner, the company (Tek), the universe, or the transformer itself? ;-)

Fun off

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