Marek Thanks. I have the schematic and can now see that its a 18V regulator. So thats only 3 watts. Its a classic differential regulator so it can accept a wide range of transistors because the circuit has quite a bit of gain. If your transistor is being destroyed then potentially there is an oscillation in the circuit. A scope on the +18 should tell you. Other then that the current should start high at .46 amps as you mention in by 20 minutes should drop down to 46 ma as a guess. If it stays high the ovens overheating and as you are concerned perhaps a bad themistor. Let us know how you are doing. Regards Paul WB8TSL
On Mon, May 9, 2022 at 9:11 AM Marek Doršic <marek.dor...@gmail.com> wrote: > 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. _______________________________________________ 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.