| Electronics > Projects, Designs, and Technical Stuff |
| Inexpensive Dual NPN Transistor in Metal Can Package? |
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| Wolfgang:
... eBay is full of transistor array offerings. I like the classic ones best, and their matching is a lot better than discrete single transistors. |
| markce:
Hi Chris, BCY89 is BP 5.50 incl P&P on ebay. |
| spec:
--- Quote from: Chris56000 on January 25, 2019, 07:18:33 pm ---Hi! I'd like to try experimenting with the circuit for the Audio Sweep Generator here:– https://www.americanradiohistory.com/Archive-Poptronics/70s/1973/Poptronics-1973-10.pdf . . .but I'm having trouble finding a dual NPN TO–78 transistor that doesn't cost an arm and a leg–can anybody recommend one? --- End quote --- Hi Chris56000 The image below shows the short-form data for the Fairchild 2N49555 matched NPN BJT pair. There in nothing very special about the 2N49555, going by its data and the application in the sweep generator. It is simply being used as a pair of matched super diodes, where the exponential VBE/ICB characteristic provide a logarithmic transfer function, and hence a logarithmic sweep. There are many modern, low-cost, plastic-case, matched NPN BJT pairs that would do the job (a metal case is unimportant). One of the most popular NPN matched pairs is the BCM847xx (SOT457 is the largest case). But make sure you buy from a reliable source, or you may just get two transistor dies stuck in the same case. UPDATE#1: just noticed that schmitt trigger has already suggested the BCM847 in reply #8 (I said it was popular ;D) https://assets.nexperia.com/documents/data-sheet/BCM847BV_BS_DS.pdf |
| Kleinstein:
That circuit is full of EOL parts. The dual transistor is just one of them and relatively easy to replace with 2 matches transistors. The ICL8038 is also hardly available anymore and here there is not easy replacement. The original XR2206 is also difficult to get an the Chinese copy is slight different (lower max supply,...). |
| spec:
--- Quote from: Kleinstein on January 27, 2019, 05:54:00 pm ---That circuit is full of EOL parts. The dual transistor is just one of them and relatively easy to replace with 2 matches transistors. The ICL8038 is also hardly available anymore and here there is not easy replacement. The original XR2206 is also difficult to get an the Chinese copy is slight different (lower max supply,...). --- End quote --- It is a brave man who tries to build and test that circuit. I can only imagine that the OP is ding it for nostalgic reasons. :) |
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