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Discussion in 'Amplitude Modulation' started by K4KYV, May 25, 2019.

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  1. K4KYV

    K4KYV Premium Subscriber QRZ Page

    Another perfect example is the sheet-beam deflection tube, like the 7360. Those probably made the best mixer, converter and detector devices ever developed. They were sensitive and had very linear characteristics, producing minimal spurious intermodulation products, although 60~ a.c. hum could be a problem from the magnetic fields produced by the filament and nearby transformers. Eclipsed by solid state technology just as they were getting off the ground, and now hard to find and probably way too expensive for the typical homebrew project.

    Also, the subminiature tubes that began to appear after WWII, some with wire pins arranged in a circle to fit into a socket, while others had longer wire leads intended to be soldered in. There are still loads of those out there crammed away in junkboxes and no doubt many have been thrown away. One problem is that characteristics data on those tubes was always difficult to impossible to find and many were tossed because no-one could find information on them, although that has become more widely available with the advent of the internet.

    Those would likely have soon developed into the standard variety of tubes, just as 7- and 9- pin miniatures replaced octals, which in turn had replaced the older glass tubes with 4, 5, 6 and 7 pin bases. Solid state technology emerged before that was able to happen.
  2. N2EY

    N2EY Premium Subscriber QRZ Page

    I have used a 7360 as the receiving mixer in the Southgate Type 7 for more than 25 years. They are not rare; just expensive unless you get lucky.The 6JH8 and 6ME8 are less well known beam deflection tubes made for TV use.

    I got lucky at hamfests back in the 1980s and acquired a supply.

    How good the 7360 and similar tubes really are is somewhat debatable. One thing is for sure: their potential in receiving applications was never fully developed.

    The circuitry to use them in balanced applications is considerably more complex than, say, a Pullen mixer, making them less attractive to designers.

    They were originally developed for hearing aids but really came into their own in the proximity fuze of WW2. The proximity fuze was so secret that its story has only been recently told (really good ER article, years ago).

    Doubtful. The power handling limitations of submininiatures would be a major factor. Also cost.

    What really pushed silicon to the forefront IMHO was when the cost (both dollars and power requirements) became less than hollow state. This happened first in computers and portable/mobile applications, then gradually took over everything else.

    73 de Jim, N2EY
    Last edited: Aug 19, 2019
    WA7PRC likes this.
  3. K4KYV

    K4KYV Premium Subscriber QRZ Page

    Back in the 1970sI built up a balanced modulator using a 7360, feeding a 64 kHz asymmetrical passband telephone multiplexing mechanical filter in a SSB exciter project. It worked very well with negligible audible distortion listening with a VLF receiver. My intention was to further mix the 64kHz SSB signal to an intermediate frequency and then up to the amateur frequencies for a homebrew SSB transmitter, but got sidetracked with other projects and lost interest in the SSB project before it was finished.

    Some of the TV versions of the tube had the cathode or filament internally connected to one of the other elements, making it less useful for balanced applications, IIRC.

    A few years ago I found a batch of n.o.s. 7360s for about $10 on an internet forum. I ordered the whole lot, which he sent via Priority Mail in one of those USPS self-sealing flat-rate boxes. When the parcel arrived, the self-seal adhesive had failed, the box had opened in transit, and all I got was the empty box. He reimbursed my money, but I was very disappointed that the tubes got lost - a half-dozen fewer 7360s on the planet. I have 2 or 3 good ones in my junk box, but when I build anything with near-unobtanium I like to have more than that for spares.
  4. KM1H

    KM1H Ham Member QRZ Page

    A "small" detail often overlooked by the usual suspects. The 1959 released 7360 was specifically developed as a Special Purpose tube for use in SSB and DSB suppressed carrier applications, such as Balanced Modulator, Balanced Mixer, and Frequency Converter applications.

    The consumer grade ones mentioned, plus the 6AR8, have their own balance issues but are reportedly good as synchronous detectors. The 6AR8 was pulled from production due to the problems and show up very cheap still NIB for some applications,

    I replaced the 6BA7 mixers in my 75A4 in 1965 with 7360s and the reception improvement was an eye opener. Along with a 6GM6 in the RF stage the NF on 10M is around 6dB which opened up several new levels of signals along with far superior signal handling.

    I picked up a NIB sleeve of them some years ago for $10 total but so far the second set in the A4 from ~ 1995 are holding up well as the receiver isnt used as the main station radio any longer.

  5. KA4KOE

    KA4KOE Ham Member QRZ Page

    We miss you Paul over at AM Classic. We're almost at 3100 folks.

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