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

[rfnuts via time-nuts]

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 control the heater power, is 
mounted in the center of the housing cover, to which the SMA sockets are 
also attached.


I think the heater is directly connected to 24V, while only the control 
circuit is supplied with 18V.


Adrian

Am 10.05.2022 um 01:12 schrieb Bob kb8tq:

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 ma at 24V is 1.44W. That is a
reasonable power for a functioning OCXO on a lab bench.

Bob


On May 9, 2022, at 3:32 PM, Marek Doršic  wrote:

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 also today noticed 
interestingly that touching the Q1 transistor metal case with a voltage probe 
leads to huge input current changes. While heating-up, when I touch it the 
current increases from 440mA to 460mA. When the unit was already heated, by 
touching the transistor case the input current drops from 170mA to only 60mA. I 
am not capable to understand the circuit right now, but for me this might be 
the next suspicious part.

The oven heating seems to be OK. On the PCB are pins labeled with C, B, E ( 
photo 
 here) with wires soldered 
leading directly to the heated core. I measured voltages on these pins together with the input 
current. See attached graph 

 below of first 40 minutes while the unit was heating up. I think this pins are the terminals of 
the heating transistor inside the oven and everything looks good there.  0.44A@24V = 10.5W and 
then the current settles down at about 0.17A (4W). This is quite in within spec (should be 3.5W 
after 2.5 hours warm-up).



   .marek


On 9 May 2022, at 15:54, paul swed  wrote:

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 mailto: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  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 
>> 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 

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

[Bob kb8tq]

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 ma at 24V is 1.44W. That is a 
reasonable power for a functioning OCXO on a lab bench. 

Bob

> On May 9, 2022, at 3:32 PM, Marek Doršic  wrote:
> 
> 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 also today noticed 
> interestingly that touching the Q1 transistor metal case with a voltage probe 
> leads to huge input current changes. While heating-up, when I touch it the 
> current increases from 440mA to 460mA. When the unit was already heated, by 
> touching the transistor case the input current drops from 170mA to only 60mA. 
> I am not capable to understand the circuit right now, but for me this might 
> be the next suspicious part.
> 
> The oven heating seems to be OK. On the PCB are pins labeled with C, B, E ( 
> photo 
>  here) with 
> wires soldered leading directly to the heated core. I measured voltages on 
> these pins together with the input current. See attached graph 
> 
>  below of first 40 minutes while the unit was heating up. I think this pins 
> are the terminals of the heating transistor inside the oven and everything 
> looks good there.  0.44A@24V = 10.5W and then the current settles down at 
> about 0.17A (4W). This is quite in within spec (should be 3.5W after 2.5 
> hours warm-up).
> 
> 
> 
>   .marek
> 
>> On 9 May 2022, at 15:54, paul swed  wrote:
>> 
>> 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 > > 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  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 >> >> 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 

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

[Marek Doršic]

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 also today noticed 
interestingly that touching the Q1 transistor metal case with a voltage probe 
leads to huge input current changes. While heating-up, when I touch it the 
current increases from 440mA to 460mA. When the unit was already heated, by 
touching the transistor case the input current drops from 170mA to only 60mA. I 
am not capable to understand the circuit right now, but for me this might be 
the next suspicious part.

The oven heating seems to be OK. On the PCB are pins labeled with C, B, E ( 
photo 
 here) with wires 
soldered leading directly to the heated core. I measured voltages on these pins 
together with the input current. See attached graph 

 below of first 40 minutes while the unit was heating up. I think this pins are 
the terminals of the heating transistor inside the oven and everything looks 
good there.  0.44A@24V = 10.5W and then the current settles down at about 0.17A 
(4W). This is quite in within spec (should be 3.5W after 2.5 hours warm-up).



   .marek

> On 9 May 2022, at 15:54, paul swed  wrote:
> 
> 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  > 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  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 > >> 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 

[time-nuts] Re: Can the ADEV of a GPSDO output ever be lower than the minimum of the ADEV of the internal oscilator and the ADEV of the GPS PPS?

[Attila Kinali]

On Fri, 29 Apr 2022 16:53:58 +0200
André Balsa  wrote:

> Mathematically, no, a GPSDO cannot have a lower uncertainty (ADEV) than the
> minimum observable uncertainty (ADEV) of the combined oscillator
> (disciplined clock) and PPS (disciplining clock) from the GPS receiver.
> Unless there is some magic trick to remove the uncertainty in a clock that
> I am not aware of. ;)

This is not quite true. 

Keep in mind that the *DEV metrics all implicitly assume that the noise
is Gauss distributed and has a PSD of the form of 1/f^a, a ∊ [0,4]
and a high-frequency cut-off. The moment you leave this relatively
restrictive class of functions you have to validate that the *DEV metric
you are using is still producing what you think it does. One common function
for which we have done this are quadratic functions (with noise), also
known as "linear frequency drift". But we have done so for a scant few
other functions.

If you have read my mail a few days ago, then you might have noticed that
few oscillators we have actually fit into this class. And the "worse" they
are, the less they fit. An OCXO can have sudden phase and frequency jumps.
Not to mention its temperature dependency which will lead to some phase
function which looks noise like, even slightly self-similar (another
characteristic of 1/f^a noise), but actually isn't. There is some periodic
behaviour in it, at different repetition rates, together with linear,
quadratic and cubic components. Go to a TCXO or even a simple XO and
things get even worse.

I can't go into the mathematical details as I don't have nearly enough
knowledge about the nitty gritty stuff of *DEV. But we have people here
who know way more than I do, who could chip in.

As for the case at hand. There has been a plot of the TCXO's free running
behaviour earlier. In which one could see that the TCXO had some quite
distinct frequency steps, presumably from the temperature compensation.
Between these the phase was pretty stable. Which means the ADEV gets
detoriated by the frequency steps and doesn't see these "flat" portions
inbetween, not to mention it breaks with the assumption which ADEV is
built upon. Now, if the control loop hits a sweet spot where the loop
compensates these frequency steps quickly but without degrading the 
"flat" portions inbetween, then the ADEV of the combined TCXO + PPS + control 
loop
could indeed be lower than the individual components. But without a closer
look at what happens to the phase, it is hard to tell whether this is a
genuine effect of the control loop, an artifact of the simulation or simply
a bug somewhere.

Attila Kinali


PS: Please, for the sake of all that is ticking, whenever you post an *DEV plot,
add error bars. *DEV are statistical figures. And like all statistical figures
they have an uncertainty. Without the error bars it is hard to judge whether the
values are statistically significant or just some randomly thrown dice because
of not enough data.

-- 
In science if you know what you are doing you should not be doing it.
In engineering if you do not know what you are doing you should not be doing it.
-- Richard W. Hamming, The Art of Doing Science and Engineering
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[time-nuts] Re: OSA-5400 power transistor

[paul swed]

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  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  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  > 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  time-nuts@lists.febo.com> -- To unsubscribe send
> >> an email to time-nuts-le...@lists.febo.com  time-nuts-le...@lists.febo.com>
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[time-nuts] Re: OSA-5400 power transistor

[Marek Doršic]

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/wd4yrndn4scfzov/Screenshot%202022-05-08%20at%2019.01.46.png?dl=0
 


.marek

> On 8 May 2022, at 21:05, paul swed  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  > 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 
>>  -- To unsubscribe send
>> an email to time-nuts-le...@lists.febo.com 
>> 
>> To unsubscribe, go to and follow the instructions there.
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