Replacement for Darlington D16P1

[kvandekrol]

From what I understand, a Darlington transistor is basically 2 transistors in one, where the second one amplifies the first. So even though this particular part, the D16P1, is long gone (can't even find them on ebay), there should be a way to recreate its functionality with two readily available transistors based on the specs, right?

Here's the best datasheet I could find:
http://www.datasheetarchive.com/pdf/getfile.php?dir=Databooks-3&file=Book517-24805.pdf&scan=

How would I go about finding which two transistors I could use for this? Or is there a single-package Darlington with similar specs still being made that could substitute? I looked at the MPSA12 and similar ones, which are pretty commonly used, but most of the specs weren't anything alike, and I don't know which specs are important and which aren't.

[bry melvin]

although I try to avoid them. NTE has a cross referenced part  I would carefully compare data sheets befor using it though.

[Enzo]

The voltage spec should be a minimum.  A sub can have a higher voltage spec than the original.

The current spec should be similar but not lower, so if the original is good for 200ma, than a 500ma part ought to be OK.

It is a darlington, so it has high gain.  But that can mean 1000 or 10,000, so get something in the ballpark.

What is the part used for?  if it is driving an LED then it hardly matters what you use.  If it is in the signal path, then you might want to stay close.

And if you use a MPSA12 or MPSA13, be aware the legs are in different order from your original.

[DJPhil]

It's going to be tough finding an exact match, as there have been huge improvements in semiconductor manufacture in the last 35 years or so. Still, it'll be a lot less headache than trying to use two transistors.

It does depend on the application. The most common use I can think of for such a transistor is as part of the input differential amplifier. Back then these transistors were the best way to get high input impedance in an amplifier. A good clue would be if you have two of them in your circuit, and they're near each other or perhaps even thermally coupled with a zip tie or small heatsink.

It's very likely that a darlington like this is part of an amplifier that has an overall negative feedback, so the absolute Hfe isn't likely to be important. If it's part of a differential amp configuration then what's really important is the difference in the Hfe between the two transistors (which is why they are sometimes thermally linked). In short, if you have to replace one of a differential pair then replace both.

Fairchild's MPSA14 and it's close relatives (everything marked 'sourced by process 5') are all fairly good matches. Here's a link to the Fairchild parametric search that should show you the relevant parts. The current handling and breakdown voltages are all better than the D16P1 thanks to modern technology, and this is good. The 2N5308 is a match for Vsat, which could be relevant if it's used for switching, but that's pretty unlikely in an amp. Any of these should work just fine in the signal stages of a guitar amp with very little or no noticeable difference in sound, though you never know.

More info on the application would help to be sure, but assuming it's part of a differential I'd try any two of the MPSA14 family and see how it sounds. I'd order ten or twenty, just to have them handy, but I'm weird. They're fairly cheap after all. As Enzo said, double check the pinout when you install it! You'll have plenty of lead length to match the board holes, just be sure they're all in the right spot.

although I try to avoid them. NTE has a cross referenced part  I would carefully compare data sheets befor using it though.

I understand, I hate them too. They're reliably double the price of other parts, and I've seen it much, much worse. It's not so bad on signal transistors, but analog ICs and TO3 transistor prices make me gag.

Hope that helps, I've had a bit too much coffee today. 

[kvandekrol]

Thanks for the responses! Here's more info: this would be a direct replacement for the D16P1 in the Lab Series L5 compressor circuit (Q103, here.) Having gone from a complete soldering novice a year ago to now being somewhat competent with analog circuits, primarily due to the long process of repairing an L5 (which is documented in nearly all of my previous posts on this forum ), I am toying with the idea of building an L5 preamp from scratch - for the challenge of it, and because I want to make it rackmountable. The D16P1 is the only part that isn't still available.

[J M Fahey]

Just make it out of two regular transistors.

[kvandekrol]

I checked on the NTE cross reference (NTE172A). Everything looks nearly identical (except the "maximum" ratings are of course much higher on the NTE), but I'm wondering about the gain. The D16P1 has a range of 2k-70k, while the NTE's is 7k-70k. In this application, would that make any difference?

[J M Fahey]

Don't think so.