[time-nuts] Re: OSA-5400 power transistor

Hi Bob, as by the datasheet: - input power during warmup: 11W - 3.5W operating at 25°C - warmup time 2.5 hours typ. The actual heater consists of resistor wire wound along the entire length of the cylindrical aluminum case containing the oscillator. The power transistor, which is used to

[time-nuts] Re: OSA-5400 power transistor

Hi With 24V in, 450 ma is 10.8W. That’s a pretty hearty number for warming up an OCXO. That power would not be going through the 18V regulator for a couple of reasons. Once warmed up, 170 ma at 24V is 4.08W. That’s more than a functioning OCXO should pull at typical lab bench temperatures. 60

[time-nuts] Re: OSA-5400 power transistor

Hi Paul, thanks for your insight. Sadly there is no oscillations on the 18V. The problem must be somewhere else. What I just do not understand is, why it starts working for couple of hours when I changed the Q4 PNP transistor. And now all voltages seems to be fine and it did not work. I

[time-nuts] Re: OSA-5400 power transistor

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

[time-nuts] Re: OSA-5400 power transistor

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

[time-nuts] Re: OSA-5400 power transistor

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