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I'm trying to build a buzzbox from old schematics from the 70s. The general idea is to re-purpose a (morse) code practice module. The module isn't sold anymore but I have the schematics:

code pratice module schematic

I've been able to find the specs for the transistors as follows:

Number Family Diss., mW VCBO V VEBO V Ic mA Typ Hfe Type Case Style Cat. No.
RS-2021 Gen. Purpose Amp and Med. Power Switch 350 12 4 80 30 PNP TO-92 276-2021
RS-2031 Gen. Purpose Audio Amp 200 30 6 50 120 NPN TO-92 276-2031

I've also found a website to help find transistors remplacements but :

  • I don't have values for all fields
  • I get a ton of results which I can't tell apart.

Can you help me ?

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  • \$\begingroup\$ What's the typical battery voltage? \$\endgroup\$
    – Lundin
    Commented Jul 14, 2022 at 14:12
  • \$\begingroup\$ The article shows two AA battery cells (3V). The PNP output transistor saturates with 0.2V then the max current is 2.8V/8 ohms= 350mA. The max allowed current in a 2N4403 is 600mA so it will be fine. \$\endgroup\$
    – Audioguru
    Commented Jul 14, 2022 at 14:40
  • \$\begingroup\$ It could be educational to build a test rig on perfboard or circuit board with sockets for the transistors, then try various ones. Will find that some devices work better than others in this role. \$\endgroup\$
    – rdtsc
    Commented Jul 14, 2022 at 15:21
  • \$\begingroup\$ The transistors don't do much that the switch does alone with a battery and series cap with a 1.5 or 9V battery That cct could be improved \$\endgroup\$
    – D.A.S.
    Commented Jul 14, 2022 at 15:22
  • \$\begingroup\$ I built the circuit with a BC546 and 2N2907. It didn't work unless I increased the value of the resistor at the top. \$\endgroup\$
    – Mattman944
    Commented Jul 16, 2022 at 7:46

1 Answer 1

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Any general purpose type will do e.g. 2N4401/2N4403.

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  • \$\begingroup\$ Thanks! I'll try ordering that and see how it goes. \$\endgroup\$
    – samcla
    Commented Jul 14, 2022 at 18:40

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