The Tektronix 647A is an improved version of the 647, with the main enhancement being doubling the bandwidth to 100 MHz.

Tektronix 647A
100 MHz scope
647A front view

Produced from 1967 to 1974

Manuals

Tek also introduced two new plug-ins with the 647A. The 10A2A is an improved version of the dual channel 10A2 vertical plug-in, with bandwidth extended to 100 MHz. The 11B2A is similar to the 11B2 dual time base, but triggers up to 100 MHz. The 10A1 differential comparator amplifier, first introduced in 1965 for the 647, has a maximum bandwidth of 55 MHz for sensitivities of 5 mV/div and higher in the 647A. It operates down to 1 mV/div sensitivity, and includes a comparison voltage mode with a calibrated DC offset similar to that first offered in the type W plug-in.

In total, only six plug-ins were developed for the 647 series – the generic dual trace vertical 10A2 and 10A2A amplifiers, a differential comparator vertical 10A1 amplifier, and a single 11B1 and dual 11B2 and 11B2A time bases. Although it combined high performance with rugged reliability and compactness, the 647 series was one of Tek’s “orphan” scope series, a result of when it was introduced. By the time the 100 MHz 647A was announced, the majority of the R&D effort at Tek was devoted to the 7000 series, which introduced just two years later, in 1969.

The entry level 7000 series mainframe started with performance nearly the same as the top of the line 647A. With on-screen scale factor read-out, and even more compact form factor, 7000 would offer many advantages over any of Tek’s existing lines of scopes. When the work on developing plug-ins for 7000 series was ramping up, no additional plug-ins for any of the “legacy” plug-in scopes would be developed. For the 530/540/550 series which started over 20 years earlier, a large family of plug-ins were available, but for scopes which were introduced in the mid 1960s, the variety of plug-ins was very limited.

The 067-0544-00 is a calibration plug-in for the 647A.

Key Specifications

Bandwidth DC to 100 MHz (≤ 3 dB) with 10A2A plug-in
Rise time 3.5 ns
CRT T6470, P31 std / P11 opt., 6 cm × 10 cm, 14 kV acceleration
Power 108/115/122/216/235/244 VAC ±10%,selected via primary voltage selector and voltage range selector switches, 50 Hz to 60 Hz; 185W with 10A2 & 11B2 plug-in
Operating Temperature –30 C° to +65 C°
Cooling AC Fan (only in rack variant)
Thermal Protection Automatic resetting thermal cutout, in case internal temperature exceeds safe operating level
Weight 18.4 kg (40.5 lbs)

Internals

The vertical amplifier contained in the 647A indicator unit (mainframe) consists of NPN and PNP bipolar transistors. The output transistors, Q484 and Q494, are selected 2N3866 NPN transistors. The datasheet for the 2N3866 lists Its transit frequency as 800 MHz and specifies an absolute maximum value of Vceo of 30 V. The quiescent value of Vce on Q484 and Q494 is about 30 V. So it seems likely that the selection process for these transistors involved testing their performance at the high end of their specified voltage range, and probably beyond.

The power supply of the 647A is all solid state, with a zener voltage reference and NPN pass transistors. The horizontal amplifier in the 647A uses selected 2N3119 NPN bipolar transistors for the output. These are specified as having a transit frequency of 250 MHz and a Vceo max of 80 V.

Related

The Hungarian company Elektronikus Mérőkészülékek Gyára (EMG) produced a clone of 647A, the TR-4653, in the 1970s.

Pictures

R647A

Components

Some Parts Used in the 647A

Part Part Number(s) Class Description Used in
2N3119 151-0124-00 Discrete component NPN VHF power transistor 647A
2N3866 151-0211-00 Discrete component NPN VHF power transistor 647A
5642 154-0051-00 154-0079-00 Vacuum Tube (Diode) directly-heated high-voltage rectifier 310 310A 316 317 360 453 502 502A 503 504 506 513 515 516 524 529 RM529 533 533A 535 536 543 543A 543B 545 545A 545B 547 551 555 556 560 561 561A 561S 564 567 570 575 581 581A 585 585A 647 647A
T6470 154-0434-00 154-0448-00 CRT CRT 647 647A