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4x 6AG7 Amplifier

Discussion in '"Boat Anchor" & Classic Equipment' started by NW2K, Feb 11, 2019.

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  1. KM1H

    KM1H Ham Member QRZ Page

    Ummm, more misinformation from you. The only miniatures to get a VT designation were a couple of battery tubes and the 9000 series. Geez, you really dont know your subjects but post anyway.

    You still are sadly mistaken.

    See Post 111 and 115

    The 6AG7 was developed in early 1939 as a video amp tube for USN use in 1939 as the US was ramping up to eventually enter the looming war in Europe. and received the VT 247 designation. The USN already had some radars in 1938 and they needed a better video tube. It also saw limited use in the commercial TV experiments but volume was low until after the war. I never made a claim WHEN the 6AG7Y was released BUT it was after the RMA VT designations were replaced by the JAN system in 1942. If it had been earlier it would have received a VT-247A designation.

    Try to stop making up things as you go along with your versions of history just to save face.

    I might even tell you why the J-310 was a poor choice if you behave.
  2. W9BRD

    W9BRD Ham Member QRZ Page

    I'm sure that the authors of Experimental Methods in RF Design would value the feedback. As this is an experimental receiver, I just grabbed the first JFETs I found in the junkbox, and they worked fine, as expected. Their high transconductance and just tacking them in place flying-mod style made them more regenerative at 3275 kHz than the 6AS6, but that was expected, and they're now out of the picture with the installation of the doubly-balanced diode DBM. Rather than use a double-tuned bandpass filter at the input to the DBM, because I enjoy peaking a front end for max as I tune around I'm using design's original input parallel-tuned circuit to drive the gate of a J310 source follower, the low-Z output of which drives the DBM RF port handily. Even with a 6-dB pad between the J310 source and the DBM RF port the set still hears to below the band noise at 80 and 30 meters, so it's a keeper.
  3. N2EY

    N2EY Ham Member QRZ Page

    All sorts of variants and special types - and numbering schemes. Note that the VT-x list is dominated by RCA, Eimac and WE types - I wonder if "General" Sarnoff had anything to do with that?

    The BC-191/375 transmitter used the 10 and 211 types, which were OLD in 1939, let alone 1945. Yet it was the standard transmitter in USAAF heavy bombers until the AN/ART-13 came along (which was mostly used in the B-29).

    I have read that, during the 1930s, the Japanese stockpiled vacuum tubes, particularly transmitting types, imported from the USA. Their own electronics industry was developing rapidly but they realized that they'd need more than could be produced for war, so they stockpiled. Thus at least some of their designs used rather "old fashioned" tubes.

    I assume you are familiar with my personal connection to ENIAC....

    Interesting! I wouldn't do it that way, of course, but my parts supply and operating are quite different from yours. And it's an experimental rx, meant to test out concepts. That's how the Southgate Type 7 got started....

    IF feedthrough is a common problem in receivers that don't have lots of tuned circuits and gain ahead of the IF. The JMD has a simple parallel-tuned trap in the antenna lead to reject 3300 kc., how well it works is an unknown.

    Which reminds me of a story.....

    Some time back, there appeared here on the Zed the strange case of a Drake 2-B in which the 40 meter band calibration was off - WAY off. Exactly 100 kc. off. All the other bands were fine.

    The 2-B is basically an 80 meter receiver with a crystal controlled converter in front of the 80 meter section, converting the other bands down to 80, resulting in good image rejection and the same stability and calibration on all bands. The Southgate Type 4 used a similar system, as did the Drake 2-A and 2-C, the Mosley CM-1, and several Handbook receivers such as the HB-67.

    Investigation revealed that the heterodyne crystal for 40 had been changed to one that was 100 kc. different from stock, resulting in the dial shift. But...why?

    The answer was: IF feedthrough. The 2-B heterodyne scheme uses an 11 Mc. crystal so that 7.o is received with the 80 meter section tuned to 4.0, and the band tunes "backwards" - 7.1 is at 3.9, etc.

    This works fine UNLESS you want to work weak 40 CW DX and there are strong local 75 meter folks near the top end - which will get through the selectivity of the front end. If the locals are S9+30 and the IF feedthrough rejection is 60 dB, they'll be S4.

    The classic solution is to add more RF selectivity ahead of the receiver (or get a different receiver!). But the quick and easy solution was to change the heterodyne crystal so the dial shifted exactly 100 kc.

    Speaking of which....

    The Mosley CM-1, mentioned earlier, is a neat little receiver that uses only 1 tube type (6AW8A) for all functions. Interesting design - but - one of its weaknesses is IF feedthrough, which is worst on 40 meters (only 37 dB on 40, improving to 44 dB on 20, 47 dB on 15 and 52 dB on 10.)

    I discovered the ARC-5 capacitor trick almost 50 years ago. Also the capacitor from LM/BC-221 freqmeters (the Type 6 uses ARC-5, the Type 7 BC-221).

    To me 20 kHz/turn is painfully fast, but then again, I like serious IF selectivity too. 5 kHz/turn is about my limit; slower is better.

    Which raises a question....

    Looking at receiver and VFO designs from Hq, they seemed determined to use only the classic separate-dial-and-tuning-capacitor type dials, with very little reduction. 6 to 1 reduction to cover the whole band was common. Only in the late 1960s did the Miller 2 speed drive (6/36) begin to appear. Yet, at the time, ARC-5 and BC-221/LM gear-driven capacitors and dial drives were all over the place for peanuts. Why were they not used?

    In the CQ compendium book "Command Sets", there is a "Low Cost VFO" by W2EWP which is made from a Command set tx that has been cut down to move the VFO section up to the front panel. I've used that concept to build "unit VFOs" of exceptional mechanical stability, without a lot of metal work. A suitable ARC-5 tx could be had for about the price of just a typical conventional dial, back then.

    Yet the idea never seems to have gone anywhere (other than to Southgate Radio).

    73 de Jim, N2EY
  4. KM1H

    KM1H Ham Member QRZ Page

    Who developed the tube is one thing, RCA had extensive resources, but who made them during WW2 is something else. VT second, third, etc, sources were many and included GE, Sylvania, Tung Sol, Raytheon, NU, Ken Rad, Amperex, United, Cetron, Hytron, Machlett, Westinghouse, Lewis & Kaufman, and others. Several produced Eimac designs. WE owned the telephone switching exchange and much of the audio market along with early radar tubes but many others produced them during the war.

    Many VT tubes were in military use long before WW2 and I doubt Sarnoff had any control over that. Zenith and Philco would not use RCA tubes, especially the metal ones, and had Sylvania develop the Loctal for them.

  5. KM1H

    KM1H Ham Member QRZ Page

    The ART-13 was preceded by the USN ATC which became the ART-13 under the JAN standards and were used thruout naval aviation and even aboard ship. In the USAAF it was in several twin and 4 engine bombers besides the B-29 and some late production B-17's.

    My own is the ATC

  6. KM1H

    KM1H Ham Member QRZ Page

    This does not support your latest version of reality below:

    Book authors are a dime a dozen as are individual writers of questionable competence and the 2003 publication is way late for this discussion.
    Try to stay on track.....again.

    The J310 was a severely downgraded plastic version of the metal cased U-310 due to cost so grading was all over the place. Poor balance is to be expected.
    Similar with what became the MPF-102 which could be considered floor sweepings from 2N5484, 5485, and 5486 grading.

    I still have enough of the better versions of both to keep me busy.
  7. N2EY

    N2EY Ham Member QRZ Page


    Sweep tubes, most notably the 6DQ6, were considered for use in various Southgate transmitters. However, the supply of good 807s and their ability to take 150 watts DC input easily decided the issue.

    A design element in the Type 6 and 7 transmitters is the use of VR tube regulation of the final screen voltage. This serves a dual purpose:

    1) it reduces the size of bleeder resistor needed. The VR tubes are set to about 30 mA key up, which is just right for the choke input filter used with the 866A rectifiers.

    2) it permits keying the driver stage only, with fixed bias on the final. With screen-grid tubes, the grid bias needed for plate current cutoff is held to a reasonable value if the screen voltage is regulated.

    The base jumpers of all the VR tubes are wired in series with the bias interlock/warmup time delay relay coil, so that if a VR tube is removed or the bias supply fails, the plate transformer cannot be energized.

    This concept has been in operation in various tx and PSUs for almost 30 years.

    Your website has lots of interesting information. Some of my projects are here on the Zed in various threads, including the workbenches built for almost nothing (see "This Old Shack" thread).

    There are some folks who talk a good game but don't show the goods. Like those who claim WAS or DXCC or big contest scores, but then don't have the certificates/ never sent in a log/etc.

    I remember one FD group that made a big noise about how great their setup was. Turned out they did a lot of unsafe stuff, bent the rules more than a pretzel, and their results weren't all that great.

    But it didn't matter because they never sent in a log. Or, rather, a summary sheet.

    73 de Jim, N2EY
    Last edited: Apr 29, 2020
  8. KM1H

    KM1H Ham Member QRZ Page

    At least the contest scores from this station plus several awards are verifiable:p
  9. N2EY

    N2EY Ham Member QRZ Page

    So I didn't go on FD with them again.

    The contest logs and awards I have done are verifiable, except one. A few years ago, the deadline for November SS was shortened up, and I missed it by a day.

    Won't make that mistake again.

    And none of it was done using guest operators, remotes, or borrowed stations.
  10. KM1H

    KM1H Ham Member QRZ Page

    With such a primitive station I doubt if guest ops would be beating on your door.

    My contribution was assembling the gear, always at least one generation behind and bought used. Making changes to suit the application, building and installing a real antenna farm and making the coffee.

    And let an under appreciated operator turn the ole boy community on its head and even set some records. Compared to many we beat it was a KISS low buck operation. Unlike many we werent given the latest PC controlled transceivers, amps, antenna switches, other gear and free software.

    I would never use a remote and have no use for those who do in order to gain an unfair advantage over others. Some detective work has already exposed a few and their scores did not count.

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