Sourcing obsolete ICs (National DS3672N Dual Bootstrap TTL to MOS Clock Driver)

[Pat Maki]

Wondering where folks source hard to find vintage ICs from? I've

I'm Bringing a Lexicon M93 Primetime back to life and have a dead National DS3672N Dual Bootstrap TTL to MOS Clock Driver (U5 on memory board) https://www.mikrocontroller.net/attachment/312661/NATLS16103-1.pdf
I've searched high a low for a modern (or vintage) version of this, but can't find anything similar to replace it with. This is a 70's device.

 

[Khron]

Any idea what sort of voltage levels & frequencies this is supposed to put out / pass through?

You'll likely not find a pin-compatible version nowadays, but it kinda looks like similar functionality could be achieved with a CMOS 4000-series chip, and if needed, a level-shifter (NPN or single MOSFET transistor) on the input.

 

[Pat Maki]

Any idea what sort of voltage levels & frequencies this is supposed to put out / pass through?

You'll likely not find a pin-compatible version nowadays, but it kinda looks like similar functionality could be achieved with a CMOS 4000-series chip, and if needed, a level-shifter (NPN or single MOSFET transistor) on the input.

@Khron thanks. Yes, I have a second, working unit and recorded all voltages from the memory board to a spreadsheet. Thanks for suggestion, I'll pick up a couple 4000 series chips and see if I can cobble something together to match the voltages and function of the 3672.

 

[Pat Maki]

I found a seller (4 Star Electronics). If anyone out there is looking for the obsolete National Semi DS3672N, let me know if you'd be interested in going in on a group buy. Pricing is 5 for 250USD or 10 for 300USD. I only need 2. My use is in the Lexicon M93 PrimeTime. Its a Dip8 and sits on the front end of the main memory board.

 

[Pat Maki]

@Khron do you know how to determine what inductance frequency to choose for an inductor. You can see in the memory board schematic below that the inductor (L1) feeds into a 12V power regulator. on the other side are a bunch of DRAM and flip flops etc...Any idea what frequency needs to be considered? I found this advice via google, but not sure it applies to a DC circuit

 

[Khron]

That's just there for "extra" filtering, especially the higher frequencies (where linear regulators "run out of steam" / gain, and the feedback can't compensate). Not sure the actual frequency matters THAT much.

 

[Pat Maki]

@Khron thanks for the input. I've ordered a few with widely varying resonant frequencies and will start with the one in the middle....and work my way up and down as needed.

 

[Khron]

@Khron thanks for the input. I've ordered a few with widely varying resonant frequencies and will start with the one in the middle....and work my way up and down as needed.

No real point worrying about the self-resonant frequency in DC-filtering applications like this, I don't think. Just make sure the saturation current rating is at least 1A (or however much the 78xx series is rated for).

 

[Pat Maki]

Thanks @Khron. I can find the quiescent and output currents (here), but not the saturation current for the L7812ACZ. Found this formula for saturation current. "Isat = VCC/(RC + RE)". Would solving that get me the needed metric?

 

[Khron]

Saturation current concerns the inductor. 78xx will have a rated (maximum) output current.

 

[MidnightArrakis]

Wondering where folks source hard to find vintage ICs from? I've

I'm Bringing a Lexicon M93 Primetime back to life and have a dead National DS3672N Dual Bootstrap TTL to MOS Clock Driver (U5 on memory board) https://www.mikrocontroller.net/attachment/312661/NATLS16103-1.pdf
I've searched high a low for a modern (or vintage) version of this, but can't find anything similar to replace it with. This is a 70's device.

Try this:

They claim to have pieces in-stock!!! Should you actually call this place.....ask for Larry!!!




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[Pat Maki]

Try this:

They claim to have pieces in-stock!!! Should you actually call this place.....ask for Larry!!!

View attachment 128855
View attachment 128856

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Thanks for the lead @MidnightArrakis! Will give them a ring in the morning!

 

[Pat Maki]

Try this:

They claim to have pieces in-stock!!! Should you actually call this place.....ask for Larry!!!

Friendly guy indeed, however they don't have it on the shelf, so would have to source through a distributor with a minimum buy of 300 USD....same situation I've run into with another distributor. I've joined several electronics forums in the past day (all about circuits, maker pro, etc....) and posted this there as well. Will continue the search. Thanks for your support!