US and German variants of Model B

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A special version of the BBC Model B was produced for export to the USA, and to Germany. These models had a redesigned mainboard, internal shielding to reduce electromagnetic interference, and all options (Econet, 8271 disk interface, speech) fitted as standard.

The US model had modifications to its display circuitry, to suit the 60Hz refresh rate used by NTSC televisions. The German model had a translated version of MOS.

Some US Model Bs were left unsold, and were converted back to a UK specification and sold at a reduced price. These are functionlaly equivalent to a UK Model B, but the numbering of ICs and selection jumpers does not correspond to those listed in service documentation.

IC Numbers

Model A/B
UK Model Description US / German
IC01 6502 Processor  ???
IC02 6845 / 46505 CRT Controller IC34
IC03 6522 System VIA IC11
IC04 6850 ACIA  ???
IC05 SAA5050 Teletext Generator IC82
IC06 5C094 Video ULA  ???
IC07 2c199 Serial ULA IC92
IC08 81LS95 Hi-res row address buffer IC27-31?
IC09 81LS95 Hi-res column address buffer IC27-31?
IC10 81LS95 Teletext row address buffer IC27-31?
IC11 81LS95 Teletext column address buffer IC27-31?
IC12 81LS95 CPU row address buffer IC27-31?
IC13 81LS95 CPU column address buffer IC27-31?
IC14 74LS245 data bus transciever IC80
IC15 74LS273 Teletext chip buffer IC81
IC16 LM555 timer  ???
IC17 LM324 op-amp IC24
IC18 76489 sound chip IC23
IC19 LM386 amplifier IC25
IC20 74LS139 decoder  ???
IC21 74LS00 quad 2-input NAND  ???
IC22 74LS30 8-input NAND  ???
IC23 74LS30 8-input NAND  ???
IC24 74LS138 decoder  ???
IC25 74LS20 dual 4-input NAND  ???
IC26 74LS139 decoder  ???
IC27 7438 quad 2-input NAND, open collector  ???
IC28 74LS51 dual 3-input AND-OR-Invert IC44?
IC29 74LS32 quad 2-input OR  ???
IC30 74LS74 D flip-flop  ???
IC31 74LS74 D flip-flop  ???
IC32 74LS259 decoder IC18
IC33 74LS04 hex inverter  ???
IC34 74LS74 D flip-flop  ???
IC35 LM324 op-amp IC93
IC36 74LS10 triple 3-input NAND  ???
IC37 74LS04 hex inverter  ???
IC38 74LS86 quad 2-input XOR  ???
IC39 72LS283 4-bit adder  ???
IC40 74S00 quad 2-input NAND  ???
IC41 74LS02 quad 2-input NOR  ???
IC42 74LS163 binary counter  ???
IC43 74S04 hex inverter  ???
IC44 74LS74 D flip-flop IC97
IC45 74S139 decoder IC54
IC46 74S74 D flip-flop IC96
IC47 74LS86 quad XOR IC98/99?
IC48 74LS86 quad XOR IC98/99?
IC49 74LS00 quad 2-input NAND IC89/100?
IC50 74LS00 quad 2-input NAND IC89/100?
IC52 Sideways ROM IC72-75
IC53 4816 RAM (D0 /CAS1)  ???
IC54 4816 RAM (D1 /CAS1)  ???
IC55 4816 RAM (D2 /CAS1)  ???
IC56 4816 RAM (D3 /CAS1)  ???
IC57 4816 RAM (D4 /CAS1)  ???
IC58 4816 RAM (D5 /CAS1)  ???
IC59 4816 RAM (D6 /CAS1)  ???
IC60 4816 RAM (D7 /CAS1)  ???
IC61 4816 RAM (D0 /CAS0)  ???
IC62 4816 RAM (D1 /CAS0)  ???
IC63 4816 RAM (D2 /CAS0)  ???
IC64 4816 RAM (D3 /CAS0)  ???
IC65 4816 RAM (D4 /CAS0)  ???
IC66 4816 RAM (D5 /CAS0)  ???
IC67 4816 RAM (D6 /CAS0)  ???
IC68 4816 RAM (D7 /CAS0)  ???
IC69 6522 User VIA IC17
IC70 74LS244 printer buffer  ???
IC71 74LS244 1MHz bus buffer  ???
IC72 74LS245 1MHz bus transciever  ???
IC73 PD7002 analog-digital converter IC90
IC74 88LS120 RS423 transciever IC95
IC75 DS3691 RS423 driver IC94
IC76 74LS163 binary counter  ???
IC77 74LS00 quad 2-input NAND  ???
IC78 8271 floppy controller IC16
IC79 7438 quad 2-input NAND, open collector  ???
IC80 7438 quad 2-input NAND, open collector  ???
IC81 74LS393 4-bit counter  ???
IC82 74LS10 triple 3-input NAND IC36
IC83 CD4013B CMOS D flip-flop IC22?
IC84 CD4013B CMOS D flip-flop IC22?
IC85 CD4020B CMOS binary counter  ???
IC86 74LS393 4-bit counter IC4
IC87 74LS123 multivibrator  ???
IC88 Sideways ROM IC72-75?
IC89 68B54 Econet ADLC IC84
IC90 Econet clock not fitted
IC91 74LS132 quad 2-input NAND, schmitt trigger  ???
IC92 Econet clock not fitted
IC93 75159 differential driver  ???
IC94 LM319 comparator  ???
IC95 LM319 comparator  ???
IC96 74LS244 Econet station ID buffer IC90
IC97 74LS74 D flip-flop  ???
IC98 TMS6100 speech chip IC20
IC99 TMS5220 phrase ROM IC21
IC100 Sideways ROM IC72-75?
IC101 Sideways ROM IC72-75?