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UREI BL-40 Modulimiter

Discussion in 'Amplitude Modulation' started by K4KYV, Jul 13, 2021.

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  1. W3SLK

    W3SLK Ham Member QRZ Page

    K4KYV said:
    I'm glad I'm not the only one that noticed this Don. Many times I left my parts jobber, (I love that name of electronic parts stores!), wondering if I asked for the proper wattage resistors!
  2. W8KHK

    W8KHK Ham Member QRZ Page

    Don, considering the miniscule current required by the output amplifier transistors, I believe you will find that it is possible to size the wattage of the resistors such that they are small enough to fail in an open condition if there is a fault that would risk the power supply components, but, at the same time, exhibit no noticeable heating issues under normal operation. It would require quite a large current to cause significant heating in these 10 ohm resistors.

    An example comes to mind, when I performed a foot-in-mouth error when I was testing the series modulator tubes in the widow-maker breadboard setup. I connected one of my HP function generators to the grid circuit of the modulator driver tube. I forgot there was a DC bias pot connected to the grid, and I neglected to use a coupling capacitor. Fortunately, there was a 600 ohm, 1/4 watt resistor within the enclosure, in series with the output terminal, providing a 600 ohm source impedance. The resistor was vaporized by the bias supply!

    I did not have a manual for that device, so, when searching online, I discovered a reference in an HP journal, discussing new features (at that time) in the article. The last few lines of text indicated the instrument was inexpensive enough to be used in educational institutions, and it intentionally included a 1/4 watt fuse for the same reason - bonehead moves like I committed!
    WA3VJB likes this.
  3. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    Definition of jobber: one that jobs: such as

    (1) : specifically : a wholesaler who operates on a small scale or who sells only to retailers and institutions

    Years ago I set myself up a "consulting service", simply by printing a batch of business cards and letterheads. Numerous times it has enabled me to purchase items or subscribe to publications from outfits, including electronic parts suppliers, that had a policy "not to sell" to individual customers.

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