10 Meter amp Question????????

Discussion in 'Amateur Radio Amplifiers' started by KK4DLU, Jul 16, 2013.

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  1. KK4DLU

    KK4DLU Ham Member QRZ Page

    Hi. I picked up a D&A Maverick 250 amp at a swap meet a few months back for $50. the guy said it wasnt working but it would power on. I hooked it up and it wouldn't key up which lead me to believe it may be a relay, haven't really checked it out too much yet though. but i was wonder if there is anyway I could use this amp on 10 meter without alot of interference going on. I know this amp is known for its use on 11 meter. But I don't want to splatter all over the band. Would it be worth the time and effort to fix it or should i just put it back in my project box and leave it?

    Any info would be appreciated

    Thanks
    73's KK4DLU
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Accident waiting to happen.

    It "keys" with RF drive, which of course requires an input signal. The keying amplifier is a 12AQ5 tube, maybe it's missing or dead. The drivers are four 6JT6s and the output tubes are four 6LQ6s. To use it "as designed" it will only handle 3-4W drive maximum, above that and all the smoke comes out.

    The relays RL1 and RL2 are 3PDT units with 110 Vdc coils. If I were to "restore" one of these, I'd change both relays to 12Vdc coils and add a "hard keying" line that when pulled to ground (by the transceiver) activates both relays. I'd probably get rid of the "RF sensed" 12AQ5 circuit altogether, as well as the 6JT6 drivers and just couple to the cathode input circuit of the four 6LQ6s, and also add voltage stabilization to the PA grid bias supply, which in the original design was completely unregulated at ~ -10Vdc (and this would vary with grid current, which varies with drive and loading).

    It's a truly terrible design.:p
     
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    It could be that someone already tried to drive it with a HF rig.

    The tubes are worth more than the amp if they are good.

    Especially if you have some old TVs to repair.


    Have fun.
     
  4. KK4DLU

    KK4DLU Ham Member QRZ Page

    Thanks for replies guys.... I tried to drive it with an hf rig, with transceiver rf power cut all the way back just to see if it would transmit and it wouldn't. Soooooo It wasn't me that fried it :D lol
     
  5. KM3F

    KM3F Ham Member QRZ Page

    The last guy I know who tried to use an 11 m amp on 10m was a load of distortion.
    I could not convince him it wasn't good but he eventually found out so all ended well.
    Good luck.
     
  6. KM1H

    KM1H Ham Member QRZ Page

    With a bit of work and patience that would make an excellent amp for about a reliable 400-500W on 10M SSB/CW. Not a beginner project but not a throwaway either.

    The 6LQ6 is a fairly rugged tube that has distortion levels compatible with most low-mid priced HF SS rigs. A muffin fan helps reliability.

    Carl
     
  7. VK4TI

    VK4TI Ham Member QRZ Page

    down the bottom
    http://forums.qrz.com/showthread.ph...the-final-on-a-Heathkit-VL-2280-Two-Meter-Amp
     
  8. W9GB

    W9GB Ham Member QRZ Page

    D&A Maverick 250 schematic -- CB Tricks (circa 1969)
    It was always sold as illegal CB sweep-tube amp
    http://www.cbtricks.com/Amp/d_and_a/maverick_250/graphics/mavrick_250_sch.pdf

    The 2 AC transformers, normally used, in these units can be repurposed for a
    DIY build of Heathkit HP-23 or other boat-anchor HV power supply.
    The sweep tubes have a market for the FT-101 and Drake transceivers that use them.

    w9gb
     
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