Burroughs C3300

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Calculators: Desktop: Burroughs C3300 (Series C 3315)

	Size (approx):	320mm x 420mm x 112mm (w,h,d) Weight >1.5kg excluding cable
	Power:	Mains (240V 50/60 cycles), 0.145 amps, 20 watts through a fixed cable
	Display:	16 digit nixie with separate neon lights for memory one and two, error and minus indication (see more below)
	Features:	Standard four functions with register exchange, switched constant, double switched memory, change sign and decimal point selection
	Age:	1970
	Manufacturer:	Burroughs Corporation, made in Japan. Serial number 48182-J, series C 3315
	Comments:	Note this image has had the rear clipped off. Very early (first really commercially viable) calculator apparently made by Sharp in Japan for Burroughs, USA. Astounding number of components and very high quality of manufacture. There was a range of similar modes such as the C3100 and C3200 which probably also went through numerous revisions. I do not know what the "15" series suffix means: it may be a revision or territory edition. Fabulous! The logic, whilst archaic is surprisingly good with only the negative zero bug, and it's quite quick too.

Case and Design:

The base is a shallow black plastic piece whilst the top is a sturdy light grey case. The keyboard surround is smooth black plastic. Low but deep design that has a full width cooling grill at the back and another smaller one on the rear panel and loads underneath. The top surface has a deeply embossed "B" logo. The display filter is neutral plastic giving a bright, deeply inset and shadowed image. Below this, two plastic, raised and silver painted letter panels display the brand and model number. They sit in their own shallow recesses. The chunky, hollow sounding keys are laid out spaciously and work well to this day. A rear panel with the Burroughs name is held on by two screws and hides the extension connector. Sturdy but large case that was built to last - and has.

To open remove the four outer screws (two of which are very long) and the top section will lift off, to the left hand side. The four inner screws hold down the main circuit board mounts.

Display:

The main numerical display consists of 16 orange coloured nixie display tubes. Each tube has a comma for thousand indication and a dot for decimal point. There are four extra neon lamps, two with orange plastic filters for memory I and II indication and one red "E" for error indication. To the left of these is another orange minus sign.

My example appears to go through a power-up process where all the commas come on over about a ten second period.

The multiply and divide keys also have neon lights that light up when you press them.

Keys and Switches:	Appears to be designed for right handed people as all the keys are clustered over to the right. Big chunky, hollow sounding, they are typical of their era. The (K), constant and (F) keys are toggle on/off ones whilst the white multiply and divide keys have neon lights that glow orange when pressed. A switch panel to the right has the on/off switch and switches for the memories and decimal point selection.

Too many components to count in this beast. The quality of manufacturing and engineering is superb and was no doubt reflected in its enormous original price. That it still works perfectly today is a testament to the engineering and electronics. The majority of ICs are NEC (mostly NEC µPD101C, but also the µPD132C and µPD135C) but there are a few Hitachi 9003.0B (date code February 1970) as well.

Two main boards sit nearly the whole length of the case layered and supported by sturdy metal rails. The blue edge connector at the bottom goes to the keyboard assembly. Above the display you can just see the power board. At the rear are five wire/edge connectors joining all these boards together.	A closer view shows the edges of the main boards crammed with components - all the way back. There are over a fifty 14 pin DIL ICs using discrete logic to drive the calculations. The lower board has an ID mark 7309, which sounds too late to be a date code.	An even closer view of the components used to drive and switch the nixie tubes. Each has a capacitor, four resistors and a transistor, at least on this side. A large black painted metal bracket holds the display tubes in place.

The power supply board is obviously made for the European market with taps on the transformer for 200/220/240 Volts. Huge power transistors on even larger heat-sinks are made by Hitachi and are date coded 9C and 9E; March and May 1969.	The keyboard assembly is attached to the front of the case and consists of 6 metal units and additional switches. The main numerical keyboard (the large one in the middle) appears to have matrix switching rather than being individual keys. The white wire loom goes off the the left and up to...	...a multi-pin connector accessible from the rear by removing the Burroughs labelled panel. This is believed to be for a programming accessory: a unit that mimicked key presses that could be used for repeated calculations and long programmed algorithms.

Logic comments:	(CD) is used to cancel the last number entered and (C) to clear the whole calculator.
	Input overflow is not suppressed, inputting a seventeenth digit causes and overflow error and is not recoverable
	Logic is semi-RPN, to do 3-4 key in (3)(+=)(4)(-=) to give "-1"
	The change sign function (+/-) can be used in mid number entry
	Constant function is switched in with the (K) switch and operates on all four functions
	(RC) is used for register exchange, and can be used repeatedly
	The (F) key appears to set the calculator in floating point mode and suppress the trailing zeros; i.e. key in 3.1 in three digit mode will show "3.100", (F) then (+=) to show "3.1"
	Overflow shows no result and just lights the "E lamp to the right and is not recoverable
	Divide by zero shows no result and just lights the "E lamp to the right and is not recoverable
	Negative numbers are shown with an individual neon light to the right of the main display thereby allowing full sixteen digit negative numbers
	The decimal point switch can be selected between 0/1/2/3/4/6/8/12 decimal places, but not with floating decimal or trailing zero suppression. In 12 digit mode, if your result is greater than 99,999 then you start to lose digits.
	Memory store is indicated by a "I" or "II" light for memory one and two.
	In normal memory operation the black (+) and (-) keys add or subtract a number to the memory. The (I) and (II) keys recall and clear the memory and the (à) key recalls but does not clear.
	The memory switch (=SI ) sets up memory one as an automatic accumulator, enter a number, press (=+) and it is added to memory one. You do not see any results on the display until recalled.
	The memory switch (XSII ) sets up memory two as an automatic accumulator for the first operator of any multiplication calculation - though I cannot think of why that would be useful.
	My example takes around ten seconds for all the commas to light up. It also starts up with both memory indicators on with "-0" in memory one and "0" in memory two.
	This calculator suffers the negative zero bug; try (1)(+=)(2)(-=) to give "-1" now add one by (1)(+=) will give "-0"