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Calculators: Handheld: Radio Shack EC-375

Size (approx):

92mm x 170mm x 24mm (w,h,d)
Weight 198g excluding batteries


6V DC using 4 x AA size batteries.  It accepts an adapter/charger (catalogue no. 14-854) through a socket on the top side to the far right.  A note on the back warns that if you plan to use AC power for more than 2 hours, remove standard or alkaline batteries.  There is a low battery indicator and the battery compartment has a ribbon pull to help battery removal.
Case: Sturdy, bulky brick-shaped case made from dark brown and tan smooth plastic.  There is designer sculpting all over; circles on the top front, ridges going down the side and horizontal lines on the keyboard surround.  There is a metal lug for a carry strap on the left hand side near the top.  There is a similar depression on the right hand side.  A neutral display filter sits flat but slightly proud and is printed with white branding text.  It gives a clean bright display.  The matching two-tone keys are long travel soft click but rattle a fair bit.  It looks a bit like something out of Dr. Who!
Display: 8 digit blue VFD with a ninth digit for negative, low battery, error and memory indicators
Features: Standard four functions with percentages, square root and four-function memory
Age: 1975
Manufacturer: Radio Shack, a Tandy Corporation Company, Japan.  There is no serial number that I can find.  Catalogue number 65-615 and a reference number of 7A5. 


Well-built calculator with typical 70s colouring and some nice period design points.  The logic is very poor with negative zero bug, pseudo fixed decimal bug, zero square root bug, lack of input overflow suppression and no overflow recovery at all.  Well done guys ? you?ve got the lot!

Components: 1 x cpu; Toshiba T3189 5F (June of 1975?), 28 pin DIL, 0.6" width black plastic
1 x 9 digit VFD single glass tube round faced
2 x transistors
9 x diodes
7 x capacitors
17 x resistors
2 x resistor array
1 x transformer
Boards: The keyboard assembly sits loosely on top of the main cpu board (4464250003) which is held in place by four plastic lugs.
Construction: Easy to open - when you know how!  Inside the battery compartment you will see two lugs on the sides.  Push these out and the case starts to come apart.  Eventually, with gentle prizing, you will be able to lift the font off.

Logic comments: (CE) clears the last number entered whilst (C) clears the whole calculator
Input overflow is not suppressed, keying a ninth digit results in an error which is not recoverable
Negative numbers are shown with a minus in the far left (ninth) digit thereby allowing full eight digit negative numbers
There is automatic constant on multiply and divide only
Divide by zero shows zero and ?E? in the far left (ninth) digit and is not recoverable
Overflow shows the result and ?E? in the far left (ninth) digit and is not recoverable
Negative square roots are not allowed and shows zero with ?E? in the far left (ninth) digit and is not recoverable
Memory store is indicated by the far left (ninth) digit?s decimal point
Memory overflow shows the last numbered entered and a flashing decimal point in the far left (ninth) digit
The square root of zero results in the display of ?0.0000000? which remains in this form for subsequent calculations!
This calculator suffers from the pseudo fixed decimal bug; try (0)(.)(0)(0)(+)(1)(=) to give ?1.00? which will remain as a two-digit number until more precision is required
This calculator suffers from the negative zero bug; key in (1)(-)(2)(=) to give ?-1? then (+)(1)(=) will give ?-0?
Low battery status is flagged by the upper right hand vertical segment of the far left (ninth) digit on


The box measures approx. 115mm by 196mm and is 35mm deep.  It is printed in pink and black and is of odd ?opening side? construction.  It is not much bigger then the calculator so not much else went in the box.

Text on the side states ?Custom manufactured (MFD) in Japan for Radio Shack a Tandy Corporation Company.  It has the catalogue number printed on the side and the reference number 7A5 on a sticker on the bottom.  This could be a date code of January 1975.


The manual measures 100mm by 149mm and has 20 pages.  The cover is tan and black whilst the internal pages are all black only.  It is English language only manual which is pretty much full of examples.

Notable Quote: ?Your Model EC-375 Electronic Memory Calculator incorporates the very latest solid-state design and engineering.  The calculator circuitry is a single-ship MOS/LSI (Metal-Oxide-Semiconductor/Large-Scale-Integration) with the equivalent of over 6000 transistors plus other parts!? 

Printed in Japan, ref 5A5.

Here is an example page from the manual (page 7) showing the key descriptions and the use of the extra digit for indication of overflow, memory and battery status.