Re: HP 1727A CRO: Problem with the vertical output amplifier.
Just my 2 cents here, but to me it looks like crossover distortion, so
you might want to check around the base polarization of a final
push-pull amplifier or a push-pull driver. Of course could be a
malfunctioning integrated (operational) amplifier.
I have the 1727A too btw
Frank IZ8DWF
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On Thu, Feb 24, 2022 at 8:43 PM Alex_03 <plant0300@...> wrote:
The input signal for the captures was not the calibrator, it was an external function generator. I chose triangle because it makes it easiest to see the distortion on the screen, sine shows it too and obviously square does not, hence the external function generator.
I completely forgot that I had my scope in AC coupling for those captures. new ones are attached along with pics of both sine and triangle on the screen, which I just realized I never attached to my original post, oops.
Attached in order of pins 3/6, 4/5, and 12/13 of U1(hopefully). I also captured the final vertical output(AC coupled so you can actually see something).
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Re: HP 1727A CRO: Problem with the vertical output amplifier.
The input signal for the captures was not the calibrator, it was an external function generator. I chose triangle because it makes it easiest to see the distortion on the screen, sine shows it too and obviously square does not, hence the external function generator.
I completely forgot that I had my scope in AC coupling for those captures. new ones are attached along with pics of both sine and triangle on the screen, which I just realized I never attached to my original post, oops.
Attached in order of pins 3/6, 4/5, and 12/13 of U1(hopefully). I also captured the final vertical output(AC coupled so you can actually see something).
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Reminds me of a saying...
It is better to don sandals than carpet the world.
What's next?? Demanding people wear certain things (that has nothing to do with covering indecent exposure) in public or face jail time and/or fines? Oh...wait...
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File /Above 10000 to 89999/50000 to 59999/54720A/54720A_FW_EPROM_DUMP.rar deleted
#file-notice
The following files and folders have been deleted from
the Files area of the [email protected] group.
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/Above 10000 to 89999/50000 to 59999/54720A/54720A_FW_EPROM_DUMP.rar
By: boddax@...
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On 2/24/22 04:50, Roberto wrote: hi to all I have for several years dvm hp3478a I think it is good to replace the battery I have read many posts on the forum I wanted some indication where I can find the 3v battery Greetings Roberto. The Panasonic BR-2/3AE5SPN is an exact replacement and is readily available from the standard electronics suppliers. I usually purchase them from either Mouser or DigiKey in the USA. NOTE WELL: If your current battery is not dead, your meter likely still has its calibration data. If you replace the battery without taking measures to preserve that data, it will be lost, and you will have to recalibrate the meter. Many people have posted instructions on how to do that; do a web search for that. Also, while you have it open, you would do well to replace the four Rifa capacitors before they explode. They area C720, C721, C765, and C766. These are also readily available, but you must take care to purchase the proper class of capacitor (Class Y safety capacitors) as these are connected directly to the AC line. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
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Re: How can I measure the bandwidth of an audio transformer with the HP8903B ?
From the advice, it would seem that the best approach would be to build a tube driver and output stage (or modify an existing one) in such a way that it is very easy to swap the transformer with another. On the secondary, use a large rheostat of perhaps 20 ohms or more, so that you can vary the reflected impedance over a wide range.
Then use your 8903B to really make useful measurements of performance, such as BW, distortion, and power.
It would be a really nice "transformer test jig"...
Pete
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The FW change does not affect the calibration constants nor options however you might end up with a black screen, the main issue here is that the 8753E and higher used a LCD rather than a CRT display, it therefore uses a different GSP which might cause a problem?
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On Feb 24, 2022, at 03:27, LeonP via groups.io <leon.pavlovic@...> wrote:
?Hi!
I'm running FW 7.14 on my 8753D Option 000 CPU upgrade. The FW 7.14 is the latest release for the 8753D.
However, it has been mentioned several times that this CPU board can use the 8753E firmware. If I try to load the 8753E's FW 7.48 or even the 8753ES' FW 7.74, what can possibly go wrong:
1. options are erased and will need to enabled them again using the unlock codes?
2. Internal HW calibration settings are gone (this would be a major disaster)?
3. nothing of the above, the FW installation will warn me that its incompatible and no damage shall occur?
The 8753D shows only two traces (channels) and I would appreciate it very much the 4 channel feature of the 8753E/ES :)
Thanks for the help!
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Re: How can I measure the bandwidth of an audio transformer with the HP8903B ?
Bonjour how Attillo
Very fine question
Audio output Transformers with a steel core are nonlinear, the induction, and parameters vary with frequency and voltage excitation.
Thurs a network or impedance Analyzer gives only the small Signal bandwidth. the powers excitation distortion,BW and losses must be separately measured.
The subject was deeply studied at BTL in 1920s..1950s, and better windings, magnetic materials and amplifier topologies led to very wideband, low THD transformers as used in classic high end 1950s..1970s valve audio amplifiers. Marantz, Ficher, HH Scott, etc.
Low frequency 3db d¨¦pends on the primary Magnetizing inductance, and core saturation, relation to volts x seconds integral, at primary.
The High frequency 3db is limited by interwinding capacit¨¦ and leakage inductance.
Most common audio output transformers bandwidth at say 1..5 W might be 30 Hz..15 kHz.
I hope this clarifies the complicated situation.
Bon chance
Jon
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Okay, well I can't find anything amiss with C7 on A20. It measures 10uF @ 0.5 Ohms in circuit (a *very* low ESR for a 10uF 63V cap!) so I don't see how replacing it would help at all, I'm sorry to say. The search goes on!
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Re: How can I measure the bandwidth of an audio transformer with the HP8903B ?
Thank you all,
it is understood that then in real operation it will be different from the measurements made only on the transformer, but I will be able to use the measurements for a first comparison between transformers.
I agree and thank Gary Johson, I will put a resistor in series to the primary for matching the impedance, and an 8 ohm resistor on the 8 ohm secondary.
Being a push-pull transformer there should be no problems related to DC current.
Jim Allyn, I only have these transformer data:
Push-pull transformer for EL34 valves.
Secondary impedances: 4 and 8 ohms.
Maximum power: 40W.
-- Cheers
??? Attilio
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Hi!
I'm running FW 7.14 on my 8753D Option 000 CPU upgrade. The FW 7.14 is the latest release for the 8753D.
However, it has been mentioned several times that this CPU board can use the 8753E firmware. If I try to load the 8753E's FW 7.48 or even the 8753ES' FW 7.74, what can possibly go wrong:
1. options are erased and will need to enabled them again using the unlock codes?
2. Internal HW calibration settings are gone (this would be a major disaster)?
3. nothing of the above, the FW installation will warn me that its incompatible and no damage shall occur?
The 8753D shows only two traces (channels) and I would appreciate it very much the 4 channel feature of the 8753E/ES :)
Thanks for the help!
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4145B Boot Disk, photo of original?
Hi all,
Does anyone have an original 4145B boot disk they can take a photo of the label?
I want to make my own labels, so wouldn't mind replicating the original disk label if possible.
Thanks!
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Re: How can I measure the bandwidth of an audio transformer with the HP8903B ?
You will need to match the source and load impedances to get an accurate result. Ideally you should also pass the same DC current through the core as the quiescent current of the amplifier as a DC current will tend to shift the B-H curve of the core, reducing inductance and therefore changing the frequency response. I've done similar with HF transformers in the past.
Thanks Gavin
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Re: How can I measure the bandwidth of an audio transformer with the HP8903B ?
Do you have any specs on the transformer?? Like input and output impedances?? What tubes will it be used with?? Output impedance 4/8/16 ohms?
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Re: How can I measure the bandwidth of an audio transformer with the HP8903B ?
To obtain a good measurement of BW in an impedance matching transformer like this, it does indeed need to be tested with correct terminations on both sides. Since the output of your generator is an accurate wideband 600 ohms, you can pad that up with a series resistance to match the transformer's primary. Then terminate the secondary with 8 ohms or whatever load you want. The measurement side of the instrument is hi-Z so it won't load that. If you don't know the impedance of the primary, you can determine that by measuring the open-circuit voltage gain of the transformer at 1 kHz, then take the square of that to get the impedance ratio. Of course, the real world is nothing like this test! Effective impedance at the plates of the tubes is neither flat nor purely resistive, and loudspeaker impedance varies all over the place. I've always considered such a test as a validation of the transformer specs, and it's also useful when making comparisons.
DC bias is of no concern since the push-pull topology applies B+ via a center tap, so the dc fields cancel.?
-Gary NA6O
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Re: HP 1727A CRO: Problem with the vertical output amplifier.
On Wed, Feb 23, 2022 at 06:05 PM, Alex_03 wrote:
pins 7 and 5 same as U1 pins 12 and 13.
U2 pin 6: 20V
U2 pins 2 and 3: 42V?
Should pin 6 be that high? obviously it is outputting current to the 15V rail, about 155mA, but I don't know.?
-------- These voltages look pretty much on target. Take a look at the voltages on 1725A schematic that uses the same ICs. I agree it is an interesting choice to back feed +15V supply. It saves some power by re-using the current but it is unusual.? Nothing looks off in DC sense. Your scope waveforms were with AC coupling, it is possible that there is was a large DC signal during the scope capture. What are you using as the input signal (if calibrator output why is it triangle shaped)?? I recommend looking at U1 pins 3/6, 4/5, 12/13 with DC coupling on your scope.? Ozan
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These days, with the huge pixel counts on "modern" smartphones, pics do often carry very few information compared to the size of the file.
A great tool is "ImageOptim". Its free. Just drop a pic on it, and its size can be reduced up to a factor of 10 or more, often without visible degradation to the pic.
cheers
Martin
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Re: How can I measure the bandwidth of an audio transformer with the HP8903B ?
I agree with Pete. You can make some estimates with small signal conditions, but the real answer lies in what it does in an actual circuit. I think it's safe to assume it will work according to its specs (if you have them), and it's probably not worth worrying about measuring and guessing based on it viewed as a lone component. If you actually build a PA with it, in a real circuit, then you can use all sorts of instrumentation to see how well it works, and tweak the design as required.
Ed
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Re: How can I measure the bandwidth of an audio transformer with the HP8903B ?
I don't know the real answer, but wouldn't it be necessary to drive the transformer from an impedance that matches the push-pull tube setup, including the source impedance *and* the DC current and such? And maybe the BW varies at different power levels also?
I could be wrong...
Pete
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Re: HP 1727A CRO: Problem with the vertical output amplifier.
pins 7 and 5 same as U1 pins 12 and 13.
U2 pin 6: 20V
U2 pins 2 and 3: 42V?
Should pin 6 be that high? obviously it is outputting current to the 15V rail, about 155mA, but I don't know.?
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Alex_03
Dave McGuire
saipan59 (Pete)
Froggie the Gremlin
Jinxie
Attilio
Jared Cabot
Jim Allyn - N7JA
Martin