Re: Crystal detector with 10dB attenuator in series - is it for matching purposes?
Hi all Yeas its a very nice tool.Mine came with
High Frequency Swept Measurements. Hardy ? ? Very good! This what I was getting at.? I have a little slide rule from HP that does the 20 LOG(1+rho1*rho2)^2? for the mismatch. Nice calculation tool. Helps when relating VSWR effects to amplitude ripple, especially in big system, where I started 50 years ago. I realize generator return loss degrades at higher frequency (what doesnt?).? J. Kruth
In a message dated 9/2/2024 6:44:52 PM Eastern Standard Time, jmrhzu@... writes:
If it helps to add some numbers to all this then consider the case up around 22GHz where the sig gen source VSWR might be 1.8:1 typical.? This is poor enough to add significant mismatch uncertainty even if you connected it to a decent 26GHz power meter to calibrate the level. The sensor VSWR might be 1.2:1 at this frequency. The poor source VSWR of the signal generator would give an overall mismatch uncertainty of +/- 0.23dB for the signal level calibration before it gets connected to the HP 8473C. If the input VSWR of the 8473C is 2:1 at 20GHz then the mismatch uncertainty is going to be about +/- 0.8dB when the sig gen is connected to it. However, if a decent isolating attenuator is used for the calibration stage, the source VSWR of the sig gen might be improved to 1.2:1.? Therefore, the calibration phase using the power meter would benefit from having the mismatch uncertainty reduced to about +/- 0.07dB. When the connection is then made to the 8473C the mismatch uncertainty (with the isolating attenuator ahead of it) should reduce to about +/- 0.27dB. In both cases, adding the isolation attenuator provides a substantial improvement in mismatch uncertainty.
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Re: Crystal detector with 10dB attenuator in series - is it for matching purposes?
Very good! This what I was getting at.?
I have a little slide rule from HP that does the 20 LOG(1+rho1*rho2)^2? for the mismatch. Nice calculation tool. Helps when relating VSWR effects to amplitude ripple, especially in big system, where I started 50 years ago. I realize generator return loss degrades at higher frequency (what doesnt?).? J. Kruth
In a message dated 9/2/2024 6:44:52 PM Eastern Standard Time, jmrhzu@... writes:
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If it helps to add some numbers to all this then consider the case up around 22GHz where the sig gen source VSWR might be 1.8:1 typical.?
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This is poor enough to add significant mismatch uncertainty even if you connected it to a decent 26GHz power meter to calibrate the level. The sensor VSWR might be 1.2:1 at this frequency.
The poor source VSWR of the signal generator would give an overall mismatch uncertainty of +/- 0.23dB for the signal level calibration before it gets connected to the HP 8473C.
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If the input VSWR of the 8473C is 2:1 at 20GHz then the mismatch uncertainty is going to be about +/- 0.8dB when the sig gen is connected to it.
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However, if a decent isolating attenuator is used for the calibration stage, the source VSWR of the sig gen might be improved to 1.2:1.? Therefore, the calibration phase using the power meter would benefit from having the mismatch uncertainty reduced to about +/- 0.07dB.
?
When the connection is then made to the 8473C the mismatch uncertainty (with the isolating attenuator ahead of it) should reduce to about +/- 0.27dB.
?
In both cases, adding the isolation attenuator provides a substantial improvement in mismatch uncertainty.
?
?
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Re: Crystal detector with 10dB attenuator in series - is it for matching purposes?
If it helps to add some numbers to all this then consider the case up around 22GHz where the sig gen source VSWR might be 1.8:1 typical.?
?
This is poor enough to add significant mismatch uncertainty even if you connected it to a decent 26GHz power meter to calibrate the level. The sensor VSWR might be 1.2:1 at this frequency.
The poor source VSWR of the signal generator would give an overall mismatch uncertainty of +/- 0.23dB for the signal level calibration before it gets connected to the HP 8473C.
?
If the input VSWR of the 8473C is 2:1 at 20GHz then the mismatch uncertainty is going to be about +/- 0.8dB when the sig gen is connected to it.
?
?
However, if a decent isolating attenuator is used for the calibration stage, the source VSWR of the sig gen might be improved to 1.2:1.? Therefore, the calibration phase using the power meter would benefit from having the mismatch uncertainty reduced to about +/- 0.07dB.
?
When the connection is then made to the 8473C the mismatch uncertainty (with the isolating attenuator ahead of it) should reduce to about +/- 0.27dB.
?
In both cases, adding the isolation attenuator provides a substantial improvement in mismatch uncertainty.
?
?
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Re: HP 141T Power Supply Help Needed
Hi.
It's just a generic term (damping is another) to slow down the response of a loop, to prevent it going unstable.
Not an uncommon issue in some linear PSU's like those -12.6V or -100V regulator topologies that are not "conventionally" laid out.
Unless you 'scope the thing, you often don't know it's gone unstable, other than some passive parts sometimes cook for no obvious reason.? (That R49 for example!? See Mike's comment in another mail.)
It is also not uncommon, when modern transistors are used to replace older failed parts (that are not available any more) and the new device has "a lot" more gain at HF than the originals, that regulator or other control loops suddenly become "unruly" under some operating conditions.
Sometimes a low value "Base Stopper" resistor (a few Ohms, or a ferrite bead) in series with the new device's Base connection can restore sanity!
Take care.
Dave B.
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Re: 8566B Can't Calibrate
I fully agree. Subbing a 10dB attn sounds like a plan to me. Unfortunately I don't have time this week, but perhaps next I'll give it a go. At any rate, it's clearly the first thing I should try.
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Jack and Bruce - many thanks. It all helps to work out what's happening.
I only posted a photo of what I saw with the default calibration where the SA is automatically set at 10dB. It's the exact same image I'm seeing when I force it into 0dB setting. So I'm getting nothing with 0 and 10dB. I've now taken pictures of what I see on the other settings from 20 to 70dB. I did try to describe these in another post, but a pictures worth a thousand words so I've attached pix for 20, 30, 40, 50, 60 and 70dB attenuation. Enjoy...
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Re: Crystal detector with 10dB attenuator in series - is it for matching purposes?
On Mon, Sep 2, 2024 at 09:53 PM, Jeff Kruth wrote:
Some of the responses did not answer the question you asked. To answer the question below: modern signal generators, like the 8340, have a leveling loop to maintain a preset level. If you investigate to practical result of using this, it basically gives an infinitely low generator VSWR (very high return loss, good match) as no external load can cause significant amplitude ripple due to mismatch, as the loop automatically corrects this. I learned this from an HP APP note many years ago..
In my experience, and this is across many decades of using all kinds of lab sig gens, the signal generators that use a classic levelling loop do not give an infinitely low generator VSWR up at high RF frequencies. This is because a compromise has to be made between the source defining resistor at the output of the levelling loop and the added ESR of all the attenuator switches and other connections/circuitry after the levelling loop. The source VSWR is often quite good at low frequencies but the ESR (and general mismatch) of everything after the levelling loop creeps up with increasing frequency and this can spoil the source match at the output port of the sig gen.
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Usually, the source impedance will be have a VSWR spec of about 1.5:1 at higher generator output levels because of this. For sig gens that operate up to about 20GHz, the source VSWR may climb as high as 2:1 in some cases.
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Once the attenuator sections get used for lower output levels, the source match should improve in most cases.
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Re: Crystal detector with 10dB attenuator in series - is it for matching purposes?
Some of the responses did not answer the question you asked. To answer the question below: modern signal generators, like the 8340, have a leveling loop to maintain a preset level. If you investigate to practical result of using this, it basically gives an infinitely low generator VSWR (very high return loss, good match) as no external load can cause significant amplitude ripple due to mismatch, as the loop automatically corrects this. I learned this from an HP APP note many years ago..
However, lets look at the return loss of a 10 dB pad with a short circuit on the end. It should have a 20 dB return loss due to the short, but in reality, it will be less due to imperfections in the actual attenuator performance. Still, adding a pad in gives a better VSWR to the crystal detector, regardless of the detector performance.
So, as to you original question, could I use a different (lower) value pad, yes, you could. It may alter this peak to peak observed ripple over a broadband but this will probably be small anyway if quality devices are used.
One caveat is that the best diode detector performance is at a level of about -20 dBm or so. If you want the best logarithmic performance, a pad may be used to reduce incident levels to achieve this, as well as provide improved broadband VSWR performance. Hope this helps. Jeff Kruth
In a message dated 9/2/2024 2:19:18 PM Eastern Standard Time, saevartj@... writes:
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All, thanks for the replies.
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Does an RF signal gen such as say 8340B generally have poor source impedance? Has someone examined this before?
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I am wondering if the problem of mismatch and standing waves is a result of a poor sig gen impedance as jmr says or a poor input impedance of the diode detector.
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Re: Crystal detector with 10dB attenuator in series - is it for matching purposes?
If it helps, this is the setup I typically use to level a microwave signal source and provide a low source VSWR. This provides levelling to the accuracy of the power meter and the source impedance is defined by the relevant series 50 ohm resistor in the twin resistor splitter.?
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In this case the DUT (device under test) would be the HP 8473C diode. The levelling system below should provide an ultra low source VSWR and quite accurate levelling. Correction factors vs frequency can be added for the power sensor efficiency if required.
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I usually automate all this via GPIB and it works really well up to the frequency limits of my test gear here.?
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Because external levelling is used, it doesn't really matter (within reason) how lossy the coax cable is at the output of the synthesised sweeper.
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Re: 8566B Can't Calibrate
Never mind my previous question - the picture you sent confirms the problem is most likely the attenuator.? I like the idea of subing a 10dB fixed for the switched attenuator followed by RECALL 8 and then 9.? This would confirm an attenuator problem.? If you go directly to replacing the switched attenuator, what is to say that it too may have a problem (unless you confirm B4 installation)
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Cheers!
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Bruce
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One more question and then I'll "buzz off" and watch.? Did you see anything when you did RECALL 8.
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I read that you did not see anything when you did RECALL 9
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If RECALL 8 worked and RECALL 9 did not,? ?The problem is possibly the adjustment of the 18.4 MHz oscillator on A4A5.??
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If neither RECALL 8 or 9 work, the attenuator is likely.? The suggestion of substituting a 10dB fixed attenuator for the variable attenuator will confirm.? Once you have substituted the 10dB, try RECALL 8 and 9.
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If they work, it is VERY likely the attenuator.? There are videos on line and significand tata on this site about how to overhaul the attenuator.? It is a serious pain, but the results are worth the effort.
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Cheer!
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Bruce
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Re: Crystal detector with 10dB attenuator in series - is it for matching purposes?
These have a DC output, not RF so input impedance of the test equipment doesn't matter. They typically feed the vertical a scope or DC? voltmeter .
The input VSWR of the 8473C is quite good up to about 18GHz, but above this a decent attenuator will have a lower VSWR.? So the attenuator acts to isolate the less than perfect VSWR of the sig gen from the less than perfect VSWR of the 8473C detector.
However, a lot depends on what frequency range you want to operate up to.
?
The source impedance of a typical sig gen will improve at lower power levels when using its internal attenuator so the sig gen might have a fairly good source match when delivering -10dBm. I've not measured the 8340B so I can't comment on this.
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However, it is unlikely to be as good as a decent 3.5mm 10dB attenuator that is rated to 26.5GHz. Every little bit helps when trying to minimise mismatch uncertainty...
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If you ultimately want to use the 8473C for external levelling of the sig gen then maybe consider using a 11667B splitter to provide the feedback path as this will have very low source VSWR when the external levelling is in closed loop.
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Re: Crystal detector with 10dB attenuator in series - is it for matching purposes?
The input VSWR of the 8473C is quite good up to about 18GHz, but above this a decent attenuator will have a lower VSWR.? So the attenuator acts to isolate the less than perfect VSWR of the sig gen from the less than perfect VSWR of the 8473C detector.
However, a lot depends on what frequency range you want to operate up to.
?
The source impedance of a typical sig gen will improve at lower power levels when using its internal attenuator so the sig gen might have a fairly good source match when delivering -10dBm. I've not measured the 8340B so I can't comment on this.
?
However, it is unlikely to be as good as a decent 3.5mm 10dB attenuator that is rated to 26.5GHz. Every little bit helps when trying to minimise mismatch uncertainty...
?
If you ultimately want to use the 8473C for external levelling of the sig gen then maybe consider using a 11667B splitter to provide the feedback path as this will have very low source VSWR when the external levelling is in closed loop.
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Re: Crystal detector with 10dB attenuator in series - is it for matching purposes?
Crystal detectors are often used after a tuned circuit that drives a 50 ohm load. Without the pad, you can't [properly align the circuit by itself.
All, thanks for the replies.
?
Does an RF signal gen such as say 8340B generally have poor source impedance? Has someone examined this before?
?
I am wondering if the problem of mismatch and standing waves is a result of a poor sig gen impedance as jmr says or a poor input impedance of the diode detector.
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I had exactly the same problem. Bought a replacement attenuator on ebay and installed it ..Fairly simple procedure.? Now I have a very happy 8566B.
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Re: HP 141T Power Supply Help Needed
Bill, ? I suggest removing the fuse F4 and measure the resistance to ground at the terminals where the white / violet wires come to the board.? With the fuse out the resistance to ground should be very high >1K Ohm.? If not remove C9 and remeasure.? If the resistance goes up then C9 is shorted.? Or there is another short on the board.? R49 should read .36 Ohms not .02 to .04.? C9 and R49 make up a phase compensation network so that the phase shift around the control loop is <than 360 degrees so that it does not become an oscillator.? A bit strange since the ESR of most lytics is about 1 Ohm the .36 in series may not do much¡? Let me know. ? Mike ?
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From: [email protected] < [email protected]> On Behalf Of Bill Berzinskas Sent: Monday, September 2, 2024 11:01 AM To: [email protected]Subject: Re: [HP-Agilent-Keysight-equipment] HP 141T Power Supply Help Needed ? Q4 collector is around 16v still.? C9 looks OK on the surface. R49 is a little hard to test but my old fluke says somewhere in the neighborhood of .02 to .04 ohm.? No heat but signs of past heat, faded color bands.??? 3.78amp from fuse to terminal with fuse unseated at on end!?? It's supposed to be a 3a fuse though.? Wild.?? ? Bill, ? What is the voltage at the collector of Q4?? Also if you have a 10 A ammeter remove F4 and measure the current.? I sounds like there is a short somewhere.? Keep the fuse in the circuit to protect the ammeter if at all possible.? Also is R49 getting hot?? Maybe a shorted C9? ? Mike ? ? Yep all purple/white disconnected on the left.? Currently almost no voltage at output of q4 emitter, -0.02.? ? It's also getting hot.? ?Wonder if it's toast bc I lost my -2.5v since.? ?? ? Bill. ? You are making progress!? Now we have to find out where the -12.6 current is going.? Especially since the driver is getting hot.? It is funny that the current limiter is showing 0V.? I think some more ohm meter checks are? in order.? I assume the -12.6 to the A5 module is disconnected.? In fact I suggest pulling all of the white / violet wires from the A2 regulator board.? What voltage is there at the emitter of the pass device Q4?? Let me know¡ ? Mike ? ? Spent some time today checking through the rest of the line - basic checks on passives look ok. Transistors look ok.? Noticed the driver getting hot though.? ?Not making any progress, despite trying to figure it out.? ?
Current measurements:? B = 2.6v? (was 23.5v)
E = 1.9v (was -17v)
Q10..
C = 2.6v? (was 23.5v)
b = 0v again E = 0v
Q11..?
C=? ~2.2v (was 23.5v)
B = -0.2v, fluctuates? (was -.64)
E = -1v, fluctuates (was 0)
In other news, I believe I have located the short on the A5 board.? ?Stray lead clipping in a very tough to see location...? ?:\? ? ??
? On Sun, Sep 1, 2024 at 4:55?PM Bill Berzinskas via <bberzinskas=[email protected]> wrote: tiny update to the above, replaced?+100v driver and that helped immensely!
+100, -100,?+248 all work, adjust and appear happy!? ?
I gained .5v on my -12.6 line, but its still sitting at -3v.? ? ? Getting closer, seeing some signs of life finally.? ? Not all the way but progress is progress.??
I've found that CR16 and CR17 were not good, and the pass trans was also not happy anymore.? ?I've replaced all of that and am now getting a whopping -2.5v!? ?10 more to go.? :-).? Will check through resistors this evening.? ? ?I'm also seeing some off voltages in my other rails, will have to go back through the?+100 and -100 lines as well.? ? ?
Current status:?
+79
-82
+217
-2.5
The purple/white wire presenting the short was easy to find, its the one going to the board just in front of the power?supply. Looks like thats A5, so I'll start mulling over the schem?for that as well.? ?
? ? ? On Sat, Aug 31, 2024 at 5:00?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? It sounds like you are on the right track!? So find out were the .04Ohm wire goes¡ ? Mike ? ? Neat trick checking for shorts.?? As you expected probably, 0.04ohm.???? I have found one purple/white wire which when removed brings that up to 384 ohm.??? I'll be out of pocket for a day but will look at the supply one more time in isolated state and then trace that wire out.??? Thank you! ? On Sat, Aug 31, 2024, 12:11?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? So you replaced the pass transistor and Q9 then it popped the 3A fuse F4.? And at that point the regulator worked but there must be a short on the -12.6V buss.? Please run an Ohm meter check on the -12.6V buss which is / are the white / violet wires from the A2 assembly.? Check R42, CR16 and Q10.? ?From my calculations the current limiter Q10 should start taking drive away from the driver Q9 at about 2.8A.? ?I take it that no plugins are installed.? The only place in the 141T that the -12.6 goes is / the? plugin connectors, the flood gun filament, and the trace align control on the front panel.? If there is a short (<4 Ohms) then you have to find which wire has that low impedance.? Let me know what you find. ? Mike ? ? Those numbers just don't make any sense.??? I pulled all the transistors AGAIN, desoldered and cleaned.? Tested them all with a meter, repopulate.??? Back to 23.5v....??? ? On Fri, Aug 30, 2024, 6:22?PM Bill Berzinskas via <bberzinskas=[email protected]> wrote: Replaced Q9, powered on and blew the fuse.? ?Replaced Fuse?+ Q9 again?+ pass transistor and no fuse pop.? ?
Not sure if better, worse or just different :-)? B = 54v?!? (was 23.5v)
E = -17v.?
Q10..
C = 54v..? (was 23.5v)
b = 0.58v (up from 0)? E = 0v
Q11..?
C= 54.7 (was 23.5v)
B = -.64
E = 0 ? On Fri, Aug 30, 2024 at 5:48?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? OK it seems that Q 9 has a base-emitter voltage of 38.5V which says that the base-emitter junction is open because a good NPN silicon transistor can only have a forward base-emitter voltage of 1V under extreme conditions.? Normally the Vbe is in the order of 0.7V. If the emitter or base connection of Q9 were open the emitter voltage will be dragged negative by R41.? That is not good for the pass transistor Q4 to see that much negative voltage because that will exceed the Vebo rating of the pass device which may degrade the Beta of the pass device.? Basically it will Zener the base emitter junction with that much reverse bias.? Typical Vebo is in the order of <10V which is in the absolute maximum ratings of the part.? A 2N3053 should work OK as the driver Q9.? Let me know how it goes. ? Mike ? ? That does make sense,?thank you for that explanation..? I do believe I've stated it backwards.? ? 22v appears on a 2n3053 that I've replaced at pin 3, which is actually the collector..? :facepalm:..? Remeasure / restate Q9..? ? On Fri, Aug 30, 2024 at 3:02?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? Lets back up a minute¡ If there is +22V at the emitter of the driver Q9 then there must be +22V at the base of the series regulator Q4 and you say that there is less than 1V ?at the emitter of the pass transistor Q4 and also no voltage at the top of R42 (the current sense resistor) then there is 22V across the base emitter junction of? Q4 and that can only be a failed device or some bad wiring or even a cracked runner on the board. A good NPN transistor has no more than 1V Vbe.? ??Does that make sense to you?? Or is the voltage at the emitter of the driver Q9 a negative 22V?? If the voltage at the emitter of Q9 is negative then what is the voltage at the base of Q9? ? Mike ? ? Ok..? I had a few bad transistors in the mix, but the one that was in the unit checks out ok.? ? ?I tossed a small handful to alleviate future issues.? ?
I spent a little time simulating this and from what I'm seeing this almost has to be a problem w/ the voltage divider / potentiometer.? ?I can do a lot of "shady" things in the sim and none of them give me issues like I'm seeing.? ?Removing R43 in the sim, or the pullup R45 seem to skew the voltages like I'm seeing.? ? ?The sim shows that the trimpot is kind of what "kicks things off", and the fact that I'm only getting about -1v here seems to further hint towards R43.? ? I don't have a 22.1k or even a 22k on hand, so I'll probably get creative to see what happens.? ?Resistance measurements on the pot itself look ok, i'm really hoping to not have to yank that thing.?? ? On Fri, Aug 30, 2024 at 11:58?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: I'll check these over lunch.? ?Interestingly, two of the original transistors in that spot cause the 3a fuse to blow.? ?Now sure if thats indicative of something else going on w/ a good transistor in the seat..? ? tbd.?? ? On Fri, Aug 30, 2024 at 11:43?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? 22V on the emitter of the driver is very strange.? It seems that the pass transistor Q2 has an open base ¨C emitter junction and a shorted collector base junction to come up with those voltages.? That would explain the ¡°on output¡± situation.?? An Ohm meter should be sufficient to check the status of Q2.? If your meter has a diode scale, that would give you a quick indication of the status of Q2.? ? I am thinking ?of designing an over voltage crowbar circuit to protect the -12.6 V supply from damaging sensitive circuits down stream of this supply if the regulator goes to an over voltage condition.? Some of the plugins appear to have a crowbar in just such a condition.? The filament of the flood gun is run from the -12.6V and in my case it went over voltage and it burned out the flood gun filament. ? ? Mike ? ? Thanks Michael,?
here's a recap what i'm seeing around the -12.6v line currently:?
?.65v at base of q11 sensor amp, .275v on collector.?? Driver has 22v on emitter, .27v on base and -.27v collector.????? Not much happening on the current limiter.?? 0v base.? ? On Fri, Aug 30, 2024 at 11:15?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? OK so you have the early version of the supply.? If you give me the voltages at the base of the driver transistors I can perhaps give you some more pointers. ? Mike ? ? correction, it did have the LAMP..? ?? ? My unit is 1615a prefix, it did have the zener and it was measuring closer to 100v instead of the expected 83 or whatever.? It has since been replaced by a pair of diodes that bring it to 89v but I have had to replace that string at least once in my travels so far, so I will eventually look for a more permanent?solution as I've read about.? ?I can check that again this evening!? ?I stopped thinking about it after I got the?+100v supply up! ? On Thu, Aug 29, 2024 at 4:50?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? There are 2 versions of this supply.? There is an early version that has a neon tube as the reference for the +100V supply and a later version that uses a 9V temp compensated Zener that is floating.? That is the reference Zener is connected from the +100V rail and the base of Q4.? It may help to know which version you have.? From my schematic the +100 V is the master and the other supplies are referenced from it.?? The one I have has a serial number prefix 2101A and it appears to be made in the late 1981 or early 1982 time frame. This one has the floating 9V Zener. ? Mike ? ? Finished that up.? ?On the -100 I can adjust up to 96v, a little low but it is adjustable so I think I should come back to that later.??
On 248v I'm currently seeing 290v, and -12v I'm seeing -1.5v.? ? ?I reckon I could go after either of them given the dependencies.? ? Will grab some measurements in between or after work today.? ? ? On Thu, Aug 29, 2024 at 10:52?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: Well, this is awkward.? ? I had replaced both Diff Amp transistors with the same part number.??
I just found that this package is actually reverse from what i removed!? ?using a dorky little? heathkit transistor tester, i found the pinout to be CBE when looking at it from the flat side.??
The center leg was bent towards the rear of the part, while the original part was bent toward the front.??
I reversed both transistors, and got -106 which i was able to adjust appropriately!? ? ??
Strange, but makes sense.? ?I have a few more of these buggers in the supply, so it sounds like I'll be sorting through that today.? ? Will report back in a bit.??
Thanks for the help ya'll!? ? On Thu, Aug 29, 2024 at 10:45?AM Frank Mashockie via <fmashockie=[email protected]> wrote: Also, don't forget about Gianni's HP e-book.? If I remember correctly, he goes into great detail about the 141T.? Here's the link.? They can be slow to download and I forget which section includes the 141T. ?
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Re: Crystal detector with 10dB attenuator in series - is it for matching purposes?
All, thanks for the replies.
?
Does an RF signal gen such as say 8340B generally have poor source impedance? Has someone examined this before?
?
I am wondering if the problem of mismatch and standing waves is a result of a poor sig gen impedance as jmr says or a poor input impedance of the diode detector.
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Re: HP 141T Power Supply Help Needed
Dave B, where can I find the terminology of "slugging" a control loop?? First I've ever heard the term and I'm intrigued.
Thanks,
Dave W
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Q4 emitter is close to 0V anyway during use.? It is grounded by R11 0.27
Ohms, as the output current sense resistor.? Q4's base should never be
+ve vs 0V by much more than a Volt or so, ever.? If it is, the device
has probably failed.
That -12.6 rail regulator layout is somewhat confusing at first, as the
pass transistor is in the raw DC +ve feed, from the top + end of C6
(5000uF think it's C6, the schematic I have is a bit fuzzy) and "drives"
into "Ground" via R11.??? The raw DC -ve (from the other end of the
above cap, is the "Output".
If you have Q10 conducting (more than +0.7 V on it's Base.)? And all
downstream loads disconnected, I'd check C9 in case that has failed
short.? The 3A fuse, would take some time to fail at 4A.
Q10 CE short/leaky could cause the -12.6 output to not come up to spec' too.
The error amp "output voltage sensing" input from the -12.6 output, is
the emitter of Q11.? It's "Reference" (Q11 Base) is set by R47 via
CR17.?? The drawing here shows the Base of Q11 at -12V, so that makes
sense for an output of -12.6V.
If the -12.6V output reduces (moves closer to Zero Volts.)? Q11 tends to
conduct less.
Then, R44 provides the drive to Q9, to in turn drive Q4 that tries to
"pull up" the top of R11, in turn "Pulling down" the raw +ve, that in
turn causes the -12.6 output to move more -ve, to where it starts to
turn on Q11, that in turn starves the drive to Q9 to cause it all to
regulate.
Q10 conducts if the current needed to get to -12.6V output correct, is
too high (some 4A or more) sensed by the voltage across R11 via CR16.
Check also C8 (? Fuzzy image)? and R46, as they "Slug" the regulator
loop, keeping it stable.
I suspect R49 is another stability enhancing component, in series with
C9 (47uF) from output to 0V.
While your at it, check the raw DC across C6 after CR1 and CR2.?? I
think it should be some 18V from the voltages marked on the schematic.
The drawing I'm looking at is at:-
Not the best quality, but if you zoom in...?? It has typical DC values
marked for normal operating conditions.
Hope something helps.
Dave B.
--
Created on and sent from a Unix like PC running and using open source software:
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Re: HP 141T Power Supply Help Needed
Q4 emitter is close to 0V anyway during use.? It is grounded by R11 0.27 Ohms, as the output current sense resistor.? Q4's base should never be +ve vs 0V by much more than a Volt or so, ever.? If it is, the device has probably failed.
That -12.6 rail regulator layout is somewhat confusing at first, as the pass transistor is in the raw DC +ve feed, from the top + end of C6 (5000uF think it's C6, the schematic I have is a bit fuzzy) and "drives" into "Ground" via R11.??? The raw DC -ve (from the other end of the above cap, is the "Output".
If you have Q10 conducting (more than +0.7 V on it's Base.)? And all downstream loads disconnected, I'd check C9 in case that has failed short.? The 3A fuse, would take some time to fail at 4A.
Q10 CE short/leaky could cause the -12.6 output to not come up to spec' too.
The error amp "output voltage sensing" input from the -12.6 output, is the emitter of Q11.? It's "Reference" (Q11 Base) is set by R47 via CR17.?? The drawing here shows the Base of Q11 at -12V, so that makes sense for an output of -12.6V.
If the -12.6V output reduces (moves closer to Zero Volts.)? Q11 tends to conduct less.
Then, R44 provides the drive to Q9, to in turn drive Q4 that tries to "pull up" the top of R11, in turn "Pulling down" the raw +ve, that in turn causes the -12.6 output to move more -ve, to where it starts to turn on Q11, that in turn starves the drive to Q9 to cause it all to regulate.
Q10 conducts if the current needed to get to -12.6V output correct, is too high (some 4A or more) sensed by the voltage across R11 via CR16.
Check also C8 (? Fuzzy image)? and R46, as they "Slug" the regulator loop, keeping it stable.
I suspect R49 is another stability enhancing component, in series with C9 (47uF) from output to 0V.
While your at it, check the raw DC across C6 after CR1 and CR2.?? I think it should be some 18V from the voltages marked on the schematic.
The drawing I'm looking at is at:-
Not the best quality, but if you zoom in...?? It has typical DC values marked for normal operating conditions.
Hope something helps.
Dave B.
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Created on and sent from a Unix like PC running and using open source software:
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Bruce,
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There's clearly a fault here as there is no signal present to adjust. I've set out more complete info on this issue in the thread entitled?
"8566B Can't Calibrate" if you have the time to read through it.
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Seems there's some sort of issue with the attenuators as I only get any kind of signal when I'm not set to 0dB or 10dB attenuation - and of course 10dB is the default attenuation during the calibration procedure!
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Jinxie
Michael A. Terrell
Jack