Audio signal generators

Discussion in 'Amplitude Modulation' started by KC2ZFA, Jul 13, 2020.

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  1. KC2ZFA

    KC2ZFA Ham Member QRZ Page

    I'm at a stage where I need one, had a busted HP200CD, so I've been fixing it for the past month. Recently I obtained the last part I needed (the low frequency transformer) so I moved to its power supply section.

    Looking at the schematic below, is the silicon rectifier orientation shown Untitled.jpeg incorrect ? or is this the "old convention" ?

    I'm baffled.

  2. NQ8J

    NQ8J Ham Member QRZ Page

    That's not right! Must have been drawn on a Friday afternoon...
    KF0AKH and W2VW like this.
  3. K4KYV

    K4KYV Subscriber QRZ Page

    I think the band printed on the body has indicated "anode" on some diodes of the past, but not sure about the schematic. Maybe someone confused the SS diode cathode symbol with the plate of a tube type diode. Regardless, I always check polarity with an ohmmeter when using a diode pulled from the junkbox.
  4. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    The diodes as shown on the schematic are incorrect if you want a positive voltage at the top of C13, which it appears is what is wanted.

    You want the diodes to conduct on the positive going sinewaves at the Red leads to get positive voltages at the top of C13, so the diode orientation as shown is incorrect.

    I finally went with an Agilent SG after I sold the last of my tube generators because the Agilent is more accurate and more reliable.

    Last edited: Jul 14, 2020
  5. KC2ZFA

    KC2ZFA Ham Member QRZ Page

    I was baffled that a glaring error was in the manual of such a popular signal generator.

    Turns out after recapping the ps that the hv, listed as 215v on the schematic (and 225v in the text of the manual) measured out at 205v while the ct to ground measures -175v instead of the -155v per the manual.

    The funny thing is the manual says that “the difference between the negative and positive voltage should be 380 volts +/-75 volts” :)
  6. K5UJ

    K5UJ Ham Member QRZ Page

    The schematic symbol for the diode is yet another example of stupidity in my opinion, in the realm of radio and electronics. I can easily see someone who is new to all this thinking the bar that's perpendicular to the wiring would be the diode plate, or anode. And why not, it certainly resembles the electrode symbol for the anode in any tube diagram and a vacuum diode is just a tube without a grid. But no, in one of many conventions that's not intuitive, that would be wrong and the diodes would be reversed. And now, after decades, it's too late to change it. So now, one must remember to ignore the bar and observe the direction of the arrow, which points to the current flow direction which is opposite to electron transfer.

    This is probably one more reason why a lot of folks who attempt to understand how their gear works, throw up their hands in confusion and give up.
  7. WZ5Q

    WZ5Q Ham Member QRZ Page

    More then likely it was drawn on a Monday morning, lol.

    In both my professional career and my hobby, I have come across glaring errors in commercial, consumer, and military schematics/manuals over the years. Not so much in the military documentation, but it happened.
  8. N2DTS

    N2DTS Ham Member QRZ Page

    When I was a quality control inspector (just out of high school) I worked in a circuit board factory and they had a board come through with the diodes reversed.
    I told the production people and they said I was wrong, told my boss and he made them correct it.
    Only about 50 boards had been stuffed but not soldered.
    I forget if the diagram was wrong or the silk screening, or why they were backwards.
    The production people did not want to hear anything that caused more work, they would rather ship a defective product then take time to correct it.
    Very short sighted...
  9. WZ5Q

    WZ5Q Ham Member QRZ Page

    That is one of my major pet peeves. I cannot stand Incompetence and being unproductive. I spent far too many years in my career fixing other peoples mistakes as well as doing the job that they were being paid good money for in order to get the job done correctly and on time. Towards the end when I was in the higher positions, anyone that would not correct their "ways" I had fired or transferred.

    There is no excuse for laziness or incompetence.
  10. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Most likely a draftsman and or an engineer had not yet as yet reconciled conventional and electron current flow through a solid state diode.

    Just remember, electron current flow goes against the diode's arrow.


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