Smaller tubes with a lot of glow?

Discussion in 'Amateur Radio Amplifiers' started by KC8QVO, Dec 26, 2019.

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  1. WA4SIX

    WA4SIX Ham Member QRZ Page

    If you want a cool looking & operating amp, look up " 2 meter stripline amp " It's not your "Ideal" amp, but simple & very pretty.
    A great starter project.

    Ed
     
  2. AH7I

    AH7I Ham Member QRZ Page

     
  3. N8FVJ

    N8FVJ Ham Member QRZ Page

    Based upon your requirement of using what you have on hand, I like the idea of the four 807s at 815 volts plate. You can produce 200 watts PEP out on 80 meters, perhaps 150 watts on 10 meters. There are older designs out there using the 807 tube.
     
  4. KC8QVO

    KC8QVO Ham Member QRZ Page

    RX1AS 2m version with a GS35b tube:
    http://home.hccnet.nl/uffe.noucha/tech/rx1as/rx1as_org.jpg

    I came across that when I was looking up ideas for my bigger amp "idea". I have a GS35b to use, but I want to get power for HF first.

    The idea with the smaller tubes (in this thread) will probably come first as I think I can make do with more of the parts I have already and have less to acquire. We'll see where things go.
     
  5. AH7I

    AH7I Ham Member QRZ Page

  6. WS1MA

    WS1MA Ham Member QRZ Page

    i recently built an amp using 6CB5A TV horizontal output tubes. Grounded Grid the input is to the cathode. I used 4 in parallel and only run 400 volts and can get over .100 mili amps per tube i figure i get 160 watts plus the driving power. It took 2 nights from my junk box to build. I use it strickly on 80 meters when things get weak
     
    W2VW likes this.
  7. N2EY

    N2EY Premium Subscriber QRZ Page

    Some issues:

    1) How much drive is required? The OP says only 5 watts drive is available.

    2) What is the input impedance? The OP's driver wants a 50 ohm resistive load.

    3) Where does one get 1625s that can be modified as described in the article? Some brands can be modified, others cannot - and the most common ones cannot.

    4) How long can one expect 1625s to last in that amplifier when running digital modes?
     
    KD2ACO likes this.
  8. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    All right, Jim. Let's design the 4-125 with 866 recs and OD3 regulators for the screen. This (at least to me so far) is the obvious amp the OP needs to fulfill the idea of this thread. It's a no brainer! :p

    ... should probably pick a band or 2 to keep it under control. 80 & 40?
     
    AH7I likes this.
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'd want to know where one can get "working" 1625s at all these days?

    They were $0.25/each in the mid-60s at Radio Row in NYC, all WW2 surplus. That was going on 60 years ago. AFAIK, nobody's manufactured any since then.

    They were so cheap (807s were about $1.50 at the time, but 1625s were literally twenty-five cents) I probably should have bought 100 of them and stored them well.:p But I didn't, and even if I had, I sure wouldn't guarantee they're still good 75 years after their date codes.
     
  10. N2EY

    N2EY Premium Subscriber QRZ Page

    They're around. I used to have dozens, but then I sold/traded them off for 807s.

    Actually they were made well into the 1960s and probably 1970s - just not in quantity.

    Why would they go bad in storage? Seal leakage isn't a problem.

    The trick of using them in grounded-grid came from the fact that, during WW2, 1625s and other types on the JAN list were made by a variety of manufacturers, and some of them didn't exactly copy the RCA design, which had the beam-forming plates bonded to the cathode inside the tube. Instead, for some reason, some of the manufacturers brought the beam-forming plates out through a separate wire and connected them at the tube pin. With a bit of care, the wires could be separated so the beam-forming plates could be electrically isolated from the cathode - but only on tubes made by those manufacturers.

    ----

    When looking at old transmitter and amplifier designs, it is important to remember a few things:

    1) Safety wasn't always up to snuff. This is particularly true in designs published in non-ARRL publications.

    2) Signal quality wasn't always that good. In particular, IMD of "linear" amplifiers......

    3) It was common to push tubes and components way beyond published ratings, because they were cheap and plentiful. 25 cents per surplus 1625 was common; I've seen ads for them at 19 cents. At those prices, even allowing for inflation, if a set of tubes lasted 6 months, you were way ahead of the game.

    But it's not 1958 any more.
     

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