Re: Checking HP 8672A output level: are these drops normal?
Dude, the loss of a good isolator is about a dB or less. The S11 and S22 are? low reflection. The reverse isolation S12 is high and what you want.
Do you even know what an isolator is? I have built them for Uncle Sam. And I read fine. You are worried about the concatenated losses? Go back to sleep or just reading about things.
For more abuse about your ignorance, just keep going.
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Re: Checking HP 8672A output level: are these drops normal?
50 years a microwave engineer ? But poor reading skills ? OP defined the problem as only measuring the amplifier. ? How is it such experience cannot read and stay in context with OPs question? ? If you are so experienced as you claim without proof (on the internet where everyone has fantastic claims o f"experience") then you know the isolator invokes its own losses. ? These losses will vary the gain figures of the amplifier. Such an experienced expert as yourself should know that. ? Therefore, your claim of "50 years of experience" is false. ? See the term "Cognitive Biases" and "Logical Fallacies" of "Pointing to Oneself as an Expert"
11.07.2024, 19:12, "Jeff Kruth via groups.io" <kmec@...>:
This is not good advice. The amplifier, to a first degree,CAN be tested with the isolators intact. This is the standeard working environment and the isolator protect the amp in-situ, thats why tey are there. It has to work with the isolators If you see hoes in response, or excess gain slope, it will occur with the isolators. J. Kruth 50 years a microwave engineer.
In a message dated 7/11/2024 12:04:33 PM Eastern Standard Time, scope.project@... writes:
?
The amplifier cannot be tested thru the isolator. That is testing the sum of both characteristics. Yes, you can do the test, but the output is depending then on losses and reflections of the isolator as well. In that case, if the isolator can be swept and its graph known, it can be compared to the response of both.
?
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Re: Checking HP 8672A output level: are these drops normal?
This is not good advice. The amplifier, to a first degree,CAN be tested with the isolators intact. This is the standeard working environment and the isolator protect the amp in-situ, thats why tey are there. It has to work with the isolators If you see hoes in response, or excess gain slope, it will occur with the isolators. J. Kruth 50 years a microwave engineer.
In a message dated 7/11/2024 12:04:33 PM Eastern Standard Time, scope.project@... writes:
?
The amplifier cannot be tested thru the isolator. That is testing the sum of both characteristics. Yes, you can do the test, but the output is depending then on losses and reflections of the isolator as well. In that case, if the isolator can be swept and its graph known, it can be compared to the response of both.
?
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Re: Checking HP 8672A output level: are these drops normal?
"Will you destroy the amplifier if the output is not loaded with 50 ohm?" ? This is microwave-energy. (6 GHz?) ?It is critical to have the exact characteristic else energy is reflected, not included in output measurment. Reflected power can cause heating, distortion etc problems. ? S11 and such: "Scattering Parameters" is teh general topic ? See ? ? Reflection Coefficient. ? Large errors can occur without proper matching. Even bends in a coax cable can cause microwave errors. ? There is no way to know if it will be damaged without knowing what amplifier device is used and its tolerance to reflected power, or, having specification to the unit. ? The amplifier cannot be tested thru the isolator. That is testing the sum of both characteristics. Yes, you can do the test, but the output is depending then on losses and reflections of the isolator as well. In that case, if the isolator can be swept and its graph known, it can be compared to the response of both.
11.07.2024, 18:19, "Erik Kaashoek" <erik@...>:
I do have a HP437B with a 18 GHz power sensor so measuring the power is not a problem. The issue is that it is not easy to disconnect the SMA connectors between the amplifier, isolator, high pass filter and YTM without disassembling a large part of the housing.
Any recommendation on how best to measure the amplifier output is recommended?
Is it possible to unscrew the amplifier from the bottom and lift it up?
Will you destroy the amplifier if the output is not loaded with 50 ohm?
Is it therefore better to measure after the isolator?
Can you bend the very thin rigid SMA coax between isolator and high pass filter easily so you can unscrew the SMA connectors?
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Re: HP 8566B - Can my high voltage transformer be faulty?
BTW, I removed and still have the HV section from an 85662A when I upgraded to an LCD. If you need parts... J.Kruth
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Re: Checking HP 8672A output level: are these drops normal?
I do have a HP437B with a 18 GHz power sensor so measuring the power is not a problem. The issue is that it is not easy to disconnect the SMA connectors between the amplifier, isolator, high pass filter and YTM without disassembling a large part of the housing.
Any recommendation on how best to measure the amplifier output is recommended?
Is it possible to unscrew the amplifier from the bottom and lift it up?
Will you destroy the amplifier if the output is not loaded with 50 ohm?
Is it therefore better to measure after the isolator?
Can you bend the very thin rigid SMA coax between isolator and high pass filter easily so you can unscrew the SMA connectors?
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Re: HP 8566B - Can my high voltage transformer be faulty?
The PDA supply MUST be stable and regulated or the size of the CRT image will keep changing, Also not a good idea to operate long term without load on high voltage winding of the HV transformer.
If it is impossible to find the correct HV multiplier it may help to look for a Tektronix CRT scope one, my guess and it is only a guess without measuring the HV transformer output is that it is a X6 one.
G Edmonds On Thursday 11 July 2024 at 15:52:48 BST, Dave Me <scope.project@...> wrote:
Idea. ? The flyback and HVM simply make a high DC voltage and low current (milli-ampere"?) ? Maybe this to replace a difficult to find HVM? Adjustable HV-DC output: ? amazon DOT com/Adjustable-Voltage-Electrostatic-Precipitator-Supply/dp/B0B4ZVG3B8 ? This would assume the sweep of the flyback is still working to drive the yoke - coils or deflection plates. ? 11.07.2024, 01:09, "saevar" <saevartj@...>:
Hi George,
I couldn't wait so I tested the method you suggested immediately and you were absolutely right. There appears a small green "window" visible (like a miniature image) on the CRT in the center and the fuse is not blown. I am thoroughly impressed.
Thanks so much!
Regards
Saevar
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Re: HP 8566B - Can my high voltage transformer be faulty?
Idea. ? The flyback and HVM simply make a high DC voltage and low current (milli-ampere"?) ? Maybe this to replace a difficult to find HVM? Adjustable HV-DC output: ? amazon DOT com/Adjustable-Voltage-Electrostatic-Precipitator-Supply/dp/B0B4ZVG3B8 ? This would assume the sweep of the flyback is still working to drive the yoke - coils or deflection plates. ? 11.07.2024, 01:09, "saevar" <saevartj@...>:
Hi George,
I couldn't wait so I tested the method you suggested immediately and you were absolutely right. There appears a small green "window" visible (like a miniature image) on the CRT in the center and the fuse is not blown. I am thoroughly impressed.
Thanks so much!
Regards
Saevar
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Re: Checking HP 8672A output level: are these drops normal?
I do not know this instrument. I assume the path of amplifier is 50 ohms?
A suggestion on "checking power level" is to use a microwave detector diode (of the type like BAT1504) and a short coaxial RG 174 cable to connect to an accurate DVM.
? The newer microwave diodes have extremely low capacitance (i.e. 0,3 pF and lower). Some in special packages have < 0,1 pF, with strip line terminations.
I would suggest to make a micro stripline of FR4 single side copper plane with 1/4 inch wide strip of also FR4 as the strip. Exact dimensions on Pasternack website micro stripline calculator. Put the diode on a cut in the strip (series).
The short RG 174 cable provides some 10's of pF for the output filtering. I also put a small ceramic trimmer of up to 40 pF for lower frequencies to tune the detector.
These diodes are very, very sensitive to reverse voltage, may be ~ 4 V.
Note to not test them with a DVM diode test which may be 10V O.C.
Put several diodes in series to increase reverse voltage and lower capacitance. These diodes have extremely low forward voltage drop at micro-ampere currents (i.e. 10s of mV).
Terminate the micro strip line in a microwave resistor. SMA connectors can conveniently solder to the micro strip line.
The micro strip configuration is inherently self shielding (but not perfect).
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Re: HP 8341B Firmware Questions
For the records:
I have an HP8340A with firmware rev. 23 of May 1985, serial prefix 2602A, which works flawlessly with my HP8510C firmware 7.14 of August 1998.
Tom
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Re: HP 8341B Firmware Questions
Hi,
My prefix is 2928A so later than that.
It mentions a "minimum of bugs" so I'm not sure which bugs the May
88 firmware might lead to, but I have not noticed any problems.
Best regards,
Job
On 11-07-2024 00:41, saevar wrote:
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Hi Job,
Thanks for the reply. That's great to hear, I was a bit worried
since I only have the May88 version as well.
FYI, I got this is info from the 8510C Service quick reference
guide (see the last paragraph):
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Re: Checking HP 8672A output level: are these drops normal?
Back to repairing the 8672A The indicator lights are now all repaired but the low output level problem is still there.? It would be nice to be able to check the output level of the power amplifier as I know the input level is good and if the output power is OK the problem must be in the YTM however the mechanical construction of the device makes it very difficult to disconnect at either points A, B or C  Is there any recommendation on how to check the output of the power amp?
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Re: HP 8341B Firmware Questions
Hi Job, Thanks for the reply. That's great to hear, I was a bit worried since I only have the May88 version as well. FYI, I got this is info from the 8510C Service quick reference guide (see the last paragraph): 
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Re: HP 8566B - Can my high voltage transformer be faulty?
Hi George,
I couldn't wait so I tested the method you suggested immediately and you were absolutely right. There appears a small green "window" visible (like a miniature image) on the CRT in the center and the fuse is not blown. I am thoroughly impressed.
Thanks so much!
Regards
Saevar
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Re: HP 8566B - Can my high voltage transformer be faulty?
FWIW, I had a very similar problem with my 3585B spectrum analyzer. I¡¯m my case the flyback had shorts. The circuits are very similar and the supply fuse (18V) would blow on power up. ?You can do a simple ring test with a signal generator and oscilloscope plus a few components (resistor/cap). You don¡¯t need a dedicated ring tester for a one off test. Mine had shorts and failed the ring test. Ended up having to find a replacement flyback from a parts unit. It might be worth to test if you haven¡¯t confirmed the HV multiplier and certainly before you buy replacement parts. You will have to remove the flyback from the unit to test it though.
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Re: HP 8566B - Can my high voltage transformer be faulty?
Hi again Saevar
I should add that if the HV multiplier has failed the oscillator will not be able to start and will draw a high current due to the load on it, it will then blow the safety fuse, just what you are seeing.
G Edmonds
On Wednesday 10 July 2024 at 21:38:06 BST, saevar <saevartj@...> wrote:
Hi all, Thanks for your valuable advice. George, what makes you conclude that the A1A11 is faulty? I am not that familiar with CRT circuitry and am therefore a bit lost as to how to test these various parts (without risking my health), i.e. ringing test and how to excite the main winding with an RF oscillator as Dave mentions. Any further advice is much appreciated. To make it more clear what is faulty is, the overview figure below shows the display circuits. On the far left is the A1A6 and in the center is A1A3 high voltage regulator. The HV oscillator does not oscillate and the fuse at the 23V supply is blown every time.?  The HV oscillator is shown in more detail in the images below with the Q7 transistor, who's collector and the 23V supply are connected to one of the primary transformer coils. The Base and the output of the OSC drive are connected to another transformer coil for feedback.  
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Re: HP 8566B - Can my high voltage transformer be faulty?
Hi Saevar
Experience, experience and experience. I have been repairing oscilloscopes now for almost 65 years. Rule one, the higher the operating voltage the more likely to fail also frequently the high voltage multiplier fails when an instrument is put back into use after not being used for some time.
The high voltage multiplier takes the high voltage from the HV transformer which is probably about 3KVAC and multiples it up to the PDA voltage of 18KVDC. It is actually a Cockcroft and Walton multiplier, Google this.
I am not familiar with this SA but you should find that the HV multiplier has three connections one of which will be a thick high voltage cable that goes directly to the CRT, a ground and an input from the HV transformer.
Locate the wire from the HV transformer and disconnect it from the HV multiplier. Well insulate this wire as it will have 3KVAC at a minimum on it.
Replace the fuse and switch the instrument on, if the fuse does not blow the problem is the HV multiplier. You may even get a CRT trace that is defocused .
Let me know what you find.
G Edmonds
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On Wednesday 10 July 2024 at 21:38:06 BST, saevar <saevartj@...> wrote:
Hi all, Thanks for your valuable advice. George, what makes you conclude that the A1A11 is faulty? I am not that familiar with CRT circuitry and am therefore a bit lost as to how to test these various parts (without risking my health), i.e. ringing test and how to excite the main winding with an RF oscillator as Dave mentions. Any further advice is much appreciated. To make it more clear what is faulty is, the overview figure below shows the display circuits. On the far left is the A1A6 and in the center is A1A3 high voltage regulator. The HV oscillator does not oscillate and the fuse at the 23V supply is blown every time.?  The HV oscillator is shown in more detail in the images below with the Q7 transistor, who's collector and the 23V supply are connected to one of the primary transformer coils. The Base and the output of the OSC drive are connected to another transformer coil for feedback.  
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Hi All,
To reseed the bubble memory on the HP3561A DSA, a special 'reseed module' is required. It was probably made by Intel.
Has anyone done this successfully and know where the reseed module can be obtained?
I asked this some time ago, but haven't resolved the problem.
Thanks,
John
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Re: HP 8566B - Can my high voltage transformer be faulty?
Hi all, Thanks for your valuable advice. George, what makes you conclude that the A1A11 is faulty? I am not that familiar with CRT circuitry and am therefore a bit lost as to how to test these various parts (without risking my health), i.e. ringing test and how to excite the main winding with an RF oscillator as Dave mentions. Any further advice is much appreciated. To make it more clear what is faulty is, the overview figure below shows the display circuits. On the far left is the A1A6 and in the center is A1A3 high voltage regulator. The HV oscillator does not oscillate and the fuse at the 23V supply is blown every time.?  The HV oscillator is shown in more detail in the images below with the Q7 transistor, who's collector and the 23V supply are connected to one of the primary transformer coils. The Base and the output of the OSC drive are connected to another transformer coil for feedback.  
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Re: HP 8566B - Can my high voltage transformer be faulty?
And 15,734 Hz in the US (NTSC).
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
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On 7/10/2024 7:57 AM, Dave_G0WBX via groups.io wrote: Or 15.625kHz in the UK.
Dave B.
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