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  1. hevans1944

    Thermocouple RF Ammeter

    RF ammeters like the ones @Y2KEDDIE has, or the simple vacuum thermocouple attached to a heater wire as in the image I posted, are functionally obsolete, replaced by better technology. However, the first principle of measuring RF power by measuring the amount of heat it produces is always valid...
  2. hevans1944

    Thermocouple RF Ammeter

    It is a four-wire device. It is hard to see in the first image I posted, but there are two wires exiting the device on the left side. Each end of the two wires is bent 90 degrees in opposite directions, more or less perpendicular to the heater wire running top to bottom. There is a paint mark...
  3. hevans1944

    Thermocouple RF Ammeter

    @dorke: I have no idea how well it would perform at RF. It would certainly require some sort of matched attenuator to prevent it from "letting the smoke out" but, as I mentioned, I am reluctant to mess with it. The HP power meters used two thermistors, both DC excited in two separate feedback...
  4. hevans1944

    Thermocouple RF Ammeter

    Here is an image of a spiffy little "true rms" converter I acquired many years ago and have been a little bit afraid to play with. The two vertical wires are where you apply a current. The two little bent wires are thermocouple leads. Inside the glass envelope is presumably a vacuum. I have no...
  5. hevans1944

    Running high current electric solenoid using a H-bridge

    @Jimbo bob: Okay, what ARE you trying to DO? Do you ride a motorcycle? If so, what is the year, make, and model? Are you disabled and incapable of foot-shifting? Are you trying to help a disabled person who wants to ride? Do you want to power-shift with the clutch engaged by interrupting the...
  6. hevans1944

    Running high current electric solenoid using a H-bridge

    I did read the application note, but without opposing coils see no way to move the actuator to a particular position. Sorry, but that's just the way magnetic fields work, permanent magnets or not attached to the actuator.
  7. hevans1944

    Op-Amp selection for inverting source signal - Bench PSU build

    I don't remember when these first became available, but we were playing with something similar back in the 1970s before digital panel meters became so inexpensive it wasn't worth the effort. I almost SIMPed when I saw a two-and-a-half digit Asian DPM for less than two bucks on eBay yesterday...
  8. hevans1944

    Thermocouple RF Ammeter

    Please post a picture showing the type and brand of RF ammeter you have. Many of these have a built-in resistance and a thermocouple that directly drives a sensitive D'Arsonval meter movement. Here is a You Tube video showing the internals of such a meter. It doesn't really matter what the...
  9. hevans1944

    Op-Amp selection for inverting source signal - Bench PSU build

    One of the nicest dual power supplies I have ever used was the HP (now Agilent) 6227B. They were a bit pricey, in keeping with Hewlett-Packard's design philosophy of not building or selling junk, but they were also virtually bulletproof. And now sometimes available on eBay for much less than...
  10. hevans1944

    Op-Amp selection for inverting source signal - Bench PSU build

    A bench power supply just makes everything easier for the hobbyist and professional alike. Meters, separate enabling switches for each output voltage, and 5-way binding posts really help to move things along while prototyping, testing, or troubleshooting projects. Sure, you can grab a wall-wart...
  11. hevans1944

    Finding the smallest possible actuator, or a new solution. Help massively needed!

    Oooh! Those pins were great for making duplicate copies on multiple layers of paper, either with carbon paper between the copies or with micro-encapsulated ink on the copy's surface. I kinda liked the noise they made as they swooped across the pin-fed paper. They could make pretty decent...
  12. hevans1944

    Finding the smallest possible actuator, or a new solution. Help massively needed!

    I have to ask this: what are you trying to DO? I realize you think you need a micro-lift to press against something. And maybe you need three of these, spaced some unspecified distance apart, perhaps mounted on a tube or solid rod of some sort. Or perhaps you need a bunch of these, arranged in a...
  13. hevans1944

    Op-Amp selection for inverting source signal - Bench PSU build

    This is a very old problem, "easily" solved by using an isolated power supply to power the meter, as in the Nuts And Volts article... which is quite good BTW. I haven't used panel meters that also have a current function "built in" to the meter, but it would not be a big deal to add an internal...
  14. hevans1944

    Finding the smallest possible actuator, or a new solution. Help massively needed!

    Given the maximum dimension requirements, this will clearly be a custom design. Piece of (expensive) cake once we know all the design parameters... Could you provide information on the total stroke required, from fully retracted to full extended? How much force must the device exert on the...
  15. hevans1944

    IF choices

    Opps! I apologize for "stealing" your link. I must have opened it in a new tab while reading your post #9, read the article, then forgot how I "happened" to have it open. <sigh> My short-term memory is becoming worse every day that I age. Anyway, I hope the link and the responses from others...
  16. hevans1944

    12v 18650 power bank and a DC jack Trouble

    So how are you planning to safely re-charge that 12 V battery pack? Best bet is to remove the individual cells and re-charge them one at a time with an approved Li-ion charger.
  17. hevans1944

    differential charge amplifier

    Try lifting the common ground connection to the two Rs resistors and applying positive and negative bias voltages. Not sure why you would want differential connections to your capacitance transducer, since it does not appear from your description to have a balanced output. Just ground your...
  18. hevans1944

    IF choices

    Not sure about other IFs, but 455 kHz was used in about a zillion superhet AM broadcast receivers dating back to the early part of the 20th Century. The reason it became so popular was a self-fulfilling feedback from the number of receivers using it and the availability of "standard" IF...
  19. hevans1944

    IF choices

    The purpose of an IF is to allow tight control of the bandwidth and gain of the IF amplifier, thus improving the selectivity of the receiver. As @davenn mentioned, some receivers (especially higher frequency receivers) have two or more IF amplifiers because of the requirements of the local...
  20. hevans1944

    Electronics question!

    Is this homework?
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