Chinese "three lamps" vacuum tube transceiver -- experiences?

Discussion in 'Homebrew and Kit Projects' started by KX4QP, Mar 31, 2019.

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  1. KB2FCV

    KB2FCV Ham Member QRZ Page

    Yep I am going to build this as designed first and then probably move it into something like a paraset. I don't think it will be too difficult. I do have plenty of variable caps I can replace the supplied ones with. Ultimately it would be fun to take this thing portable for some of the outdoor qrp events.

    On another note.. I noticed this came with a second crystal after I soldered in the 7.023 crystal. There is also a supplied 7.050 crystal which I may change out and place in the radio instead.. I feel that could be a better frequency to use?
  2. KX4QP

    KX4QP Ham Member QRZ Page

    Tetrodes. Can't say I expected that. And what look like center tap filaments, so you could run them off a single dry cell (six filament halves in parallel, though, means you'd want bigger than a AA). The 220/6 transformer, however, looks like audio impedance matching, and much bigger than it needs to be (likely what's easily available in China).

    Edit: on crystals, I'd be very tempted to install a socket.
  3. KB5PWL

    KB5PWL Ham Member QRZ Page

    Has anyone mentioned the key is switching B+? When the T/R switch is in TX, the key will have +90V on it, when unkeyed. The only reason I can think of, for keying TX B+ instead of the TX tube's cathode is, it makes the wiring simpler. That's a retro-looking knob on the key, is it plastic?
  4. KX4QP

    KX4QP Ham Member QRZ Page

    From the photographs, it appears the entire moving arm of the key is some kind of plastic. There must be a wire to the contact, or a microswitch, or something, but the knob is attached to something that will pass for acrylic until I have it in hand to determine it's something else.

    I think it might be a really good idea to install a relay (running on the filament supply?) to keep that 90V off the key contacts, even so.
  5. KB2FCV

    KB2FCV Ham Member QRZ Page

    The key is made out of plastic. There are metal brackets that screw to the base and a nut/bolt that the key pivots on. There is a spring on the bottom and some sort of terminal on the key. There isn't really anything to connect wires up to (nor do any of the product photos show the key connected). In other words, I'll probably just connect one of my straight keys up to test it.

    Yeah as far as the +90V... definitely want to be careful. I forget the voltages across the key on some of the low powered tube transmitters I have built in the past...

    Still haven't found the time to continue with making the coils.. been busy with other things around the house. I have a few ideas on winding them on the pvc pipes.
  6. K3UJ

    K3UJ Ham Member QRZ Page

    New Egg version. I must be missing something, don't see coil information.
  7. KF5FEI

    KF5FEI Ham Member QRZ Page

    I saw a similar audio amplifer kit on Banggood for under $20, but it did not include a power supply.
  8. KX4QP

    KX4QP Ham Member QRZ Page

    @K3UJ also possible I'm missing something -- I just got mine in yesterday's mail, haven't opened the box yet. Seems to me KB2FCV indicated the kit includes magnet wire, but the coil isn't supplied already wound (one resonant coil for tuning, and a smaller tickler should be needed -- same form, for most regen receivers).
  9. K3UJ

    K3UJ Ham Member QRZ Page

    Seems the same. There are three coils to wind on two forms. Mag wire supplied coiled on the form, but not wound. Schematic as no info about number of turns nor inductance value.
    Can anyone else who purchased kit assist?
  10. KX4QP

    KX4QP Ham Member QRZ Page

    I recall from YouTube (on a completely different radio) a figure of around 80 turns on the main tuning coil and 15-20 on the tickler, for a 40m regen, though that's also dependent on wire size and spacing and coil diameter and distance between the coils on the form. KB2FCV had a friend translating the manual for him, perhaps he has the figures. Otherwise, I'll see if I can wade through and just pull the numbers out of the Chinese -- can't read a single ideogram, but I can sometimes deduce what numbers mean what by where they are in the order of things and relative to each other.

    BTW, I can't be the first to notice how much you look like Duke, from the early days of the Doonesbury comic strip...

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