Smaller tubes with a lot of glow?

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

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  1. KC8QVO

    KC8QVO Ham Member QRZ Page

    Thanks for the discussion so far.

    A few thoughts to add:

    - I like the tube rectifier idea. I did not even consider that before but that is more appealing than a diode-based rectifier. I will look in to this a bit more.

    - The idea of decks/levels is what I had in mind, however I am not sure how to arrange the parts. I was originally thinking aluminum sheet metal to make the forms/boxes/decks out of. However, after looking at the W8CDX rack transmitter that looks very interesting and puts a real-world unit in view showing what can be done with "space" and parts placement - on wood decks. I like it a lot. I think a good place to start is with some particle board or plywood as a prototype base. Arrange parts on that then see how it all fits. Make changes. Then once the layout is good come up with a more permanent form to move everything to that is nicer looking = only drill the holes needed.

    - I want the design to cover all HF bands. 6 meters would be a plus. As for the single-band idea - that might work as a "proof of concept", or a starting point in the design, but I do want something that runs all bands. I'd say if I had to pick "one band" to start with it would be 40m.

    - I may have a lead on some 6146 tubes. I will investigate that and see what I can come up with there. It was only mentioned in passing. They don't fit my original idea of having all the connections/pins on the bottom, but I suppose I can loosen up on that a bit.

    - Low power drive was mentioned as being a "challenge". The idea is to boost QRP. The radios I have will do in the 10-15w range, but that isn't where I want to design to. I don't want the load on the exciter - I want to keep that low and leave the work to the amp. The idea here is to be able to run FT8, or other digital modes that have high duty cycles, without risk of burning up the finals in the exciters. Same goes for any other 100w rig I may want to run on the amp - if I can dial those back to 20w or so and have the amp crank out even more power that would be cool. As to overall limits - that is yet to be determined. The primary goal is to design around 5 watts drive to 150-250 watts out. Once that is determined - how much drive can it take safely? That will come later.
  2. N8FVJ

    N8FVJ Ham Member QRZ Page

    807 and similar multiple tubes would not work on 6 meters. I think four 6146 producing 200 watts would not work on 6 meters either.
    N2EY likes this.
  3. KC8QVO

    KC8QVO Ham Member QRZ Page

  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Wood for a permanent platform isn't a good idea, but for fooling around it might be. Particle board is heavy and if you screw something into it, then remove the screw and try the same hole again it usually won't hold; they're kind of a "drill and screw it once, and never remove that screw" material. A plank of real wood is better for this and may be lighter weight as well.

    But in any case, what I've done for decades is use real sheet metal (aluminum mostly, but galvanized or plated steel for supporting heavier stuff) and experiment with layouts on graph paper (and pencil for marking). Once the graph paper layout is sensible and everything fits neatly, I just use rubber cement to glue the graph paper to the chassis or whatever metal I'm working with and use that as the drilling/punching template. Once finished, the graph paper just peels right off leaving no trace it was ever there.

    "Pencil CAD.":)
    KC8QVO likes this.
  5. N8FVJ

    N8FVJ Ham Member QRZ Page

    100 watts output, did not poster want 150-200 watts out? The 4-125 is a perfect tube with 5 watts in producing 250 watts out including 6 meters. 2000 volts at 200ma and 2x 0B2 and one 0A2 for screen regulation of 350 volts.
    Last edited: Dec 30, 2019
  6. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    All the clues are still pointing towards the 4-125.
  7. AH7I

    AH7I Ham Member QRZ Page

    Harvey Wells TBS50, 807 final, all the way to 2 meters.
  8. N8FVJ

    N8FVJ Ham Member QRZ Page

    Errr, to produce 200 watts per the original post, it REQUIRES four parallel 807 tubes. The internal tube capacitance with four 807 tubes would struggle to make 120 watts power out on 10 meters let alone 2 meters. And, the TSB50 makes about 2 watts out on 2 meters vs 50 watts out on 80 meters! So, how does one tube directly compare to four tubes?

    BTW- if the original poster uses four 807s, it is necessary to mount the tube socket base below the metal chassis to isolate the input from the output. Then, add neutralization on plates or the amp may oscillate on 10 meters.
    Last edited: Jan 2, 2020
  9. N8FVJ

    N8FVJ Ham Member QRZ Page

    Four new RCA 807 for $48 from ERSC in FL. Poster states he has a power supply that produces 815 volts. A little high, but would work with 750 volt rated 807s. Tube data per tube:

    RF, AB1 Class
    VA: 750
    Vg2: 300
    Vg1: -35
    Ia: 15-90
    Ig2: 3ma
    Power Out: 72 watts
    Drive Power: 2.5 watts
    Last edited: Jan 2, 2020
  10. K6BSU

    K6BSU Ham Member QRZ Page

    Commercial amps tend to hide the tubes. I want them right out in front, so I had to design my own.

    This amp runs three 811A tubes (picture shows two, but later added another one.)

    "Radios that glo in the dark" 811 amp 004.jpg
    KC8QVO likes this.

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