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ortek_service · 29th Mar 2021, 4:29 pm

Yes, the 7442 can also source current but not very much - only 0.8mA, compared to its 16mA sink capability. So rather asymmetric, and you'd be unlikely to use it as a high-side driver (Plus it is low-side in the MK14, although you may be able to use some beefier high-side driver gates).
I don't think I've seen a CMOS 74HC42 etc. CMOS pin-compatible version, that would give you better high-side drive. And I presume they didn't bother with an 74L / 74LS in these, if they were design to sink quite bit of current compared to conventional L / LS TTL outputs.

I remember buying some similar looking FND500's, on a Digital capacitance meter EPE project, back in the 80's, and these may be the opposite common polarity. But I never really used it, as never found it worked too well (maybe because they said you had to use the Mullard version of the Display-counter IC, whereas I'd bought cheaper Motorola one - although I did at least mod their circuit to produce a proper square-wave clock into it)

29th Mar 2021, 4:29 pm	#292
ortek_service Octode Join Date: May 2018 Location: Northampton, Northamptonshire, UK. Posts: 1,440	Re: I found it! A very sorry looking MK14. Yes, the 7442 can also source current but not very much - only 0.8mA, compared to its 16mA sink capability. So rather asymmetric, and you'd be unlikely to use it as a high-side driver (Plus it is low-side in the MK14, although you may be able to use some beefier high-side driver gates). I don't think I've seen a CMOS 74HC42 etc. CMOS pin-compatible version, that would give you better high-side drive. And I presume they didn't bother with an 74L / 74LS in these, if they were design to sink quite bit of current compared to conventional L / LS TTL outputs. I remember buying some similar looking FND500's, on a Digital capacitance meter EPE project, back in the 80's, and these may be the opposite common polarity. But I never really used it, as never found it worked too well (maybe because they said you had to use the Mullard version of the Display-counter IC, whereas I'd bought cheaper Motorola one - although I did at least mod their circuit to produce a proper square-wave clock into it)