Yes, it is a power transistor with heatsing. Please find attachned the attachments via dropbox https://www.dropbox.com/s/efzgvs2rh8c76in/Screenshot%202022-05-08%20at%2018.58.10.png?dl=0 <https://www.dropbox.com/s/efzgvs2rh8c76in/Screenshot%202022-05-08%20at%2018.58.10.png?dl=0> https://www.dropbox.com/s/wd4yrndn4scfzov/Screenshot%202022-05-08%20at%2019.01.46.png?dl=0 <https://www.dropbox.com/s/wd4yrndn4scfzov/Screenshot%202022-05-08%20at%2019.01.46.png?dl=0>
.marek > On 8 May 2022, at 21:05, paul swed <paulsw...@gmail.com> wrote: > > Marek > No diagram included that I can see. > The next comment may be totally wrong since I have nothing to go on. > If the input voltage is 24 V and the supply is 10 V reg at .48A, then > during the initial warm up the transistor easily dissipates 6 watts. That > would be a power transistor and some form of heat sink to keep the junction > temperature reasonable. > Regards > Paul > WB8TSL > > On Sun, May 8, 2022 at 2:14 PM Marek Doršic <marek.dor...@gmail.com > <mailto:marek.dor...@gmail.com>> wrote: > >> I would like to get your thoughts on my problem with OSA-5400 oscillator. >> >> I have on old unit, which is somehow broken. I was told it was overpowered >> with voltages up to 32V (standard supply voltage is 24V) and even sourced >> with reverse polarity supply power. >> >> When I first powered it up, it draws only 2mA. I replaced what I supposed >> was a broken 10V voltage reference (how wrong I was), with a 10V zener >> diode and voilà, I had a nice steady 5MHz, 14dB signal. But only for couple >> of hours and then it died again. So I reverse engineered the schematics >> below and the part in question (Q4) is what I suppose a PNP power >> transistor. A bought a bunch of different types available. Solder in an >> 2N2905A and powered the unit. The heater went on, the unit drew 480 mA >> after power up but the output signal was still only some noisy 2mVp-p. >> After a few minutes the transistor went broken and the heater and >> everything went off. >> Then I put there a BC160-10. This seemed to be good choice. The unit >> worked again normally, with nice output signal, but again only couple of >> hours and then the signal was lost. >> But all the voltages at test pads remain as labeled on the PCB. The >> thermistor output pins on front panel are always 2 Ohms. This part in >> heated core of the unit is probably already broken. >> >> Do you have please any thoughts, what can be wrong with the unit or what >> kind of power transistor should be used (Q4). The original part has gold >> plated leads and TO-39 package. >> The resistor values are only indicative measured with multimeter while >> soldered in. >> >> .md >> >> >> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> <mailto:time-nuts@lists.febo.com> -- To unsubscribe send >> an email to time-nuts-le...@lists.febo.com >> <mailto:time-nuts-le...@lists.febo.com> >> To unsubscribe, go to and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > <mailto:time-nuts@lists.febo.com> -- To unsubscribe send an email to > time-nuts-le...@lists.febo.com <mailto:time-nuts-le...@lists.febo.com> > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.