1. You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
    Dismiss Notice

Contex 500 Tube Amp

Discussion in 'CB and Export Equipment and Accessories' started by Shadetree Mechanic, Mar 4, 2018.

  1. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

    Joined:
    Oct 23, 2017
    Messages:
    772
    Likes Received:
    473
    Hey guys,
    I just bought a Context 500 for use on 11 meters in my new little shack. Does anyone have a manual for this or know where I can get one? I am looking for information on the tuning procedure for setting the drive and the load etc. I assume it would be the same as any other amp? It has five 6LQ6 tubes and appears to be recapped. I don't have it in my hands yet, just trying to learn all I can about it. There is surprisingly little information about it when Googled. Any and all comments welcome.

    This is not the actual unit, just a picture I found of one.
    [​IMG]


     

  2. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

    Joined:
    Oct 23, 2017
    Messages:
    772
    Likes Received:
    473
    Just got the amp and took the cover off. Looks fairly clean and looks like it is all there.

    IMG_20180306_195335255.jpg

    Looks like the big caps have been replaced at some point.

    IMG_20180306_195633815.jpg
     
  3. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

    Joined:
    Oct 23, 2017
    Messages:
    772
    Likes Received:
    473
    Can anyone tell me what the indicator light on the front is? Some kind of overload indicator? Just trying to get this thing going. Any help is appreciated, Thanks.


    IMG_20180306_200212465.jpg
     
  4. nomadradio

    nomadradio Analog Retentive

    Joined:
    Apr 3, 2005
    Messages:
    1,788
    Likes Received:
    1,194
    It is wired to the tubes' heater supply. Should be a 6.3-Volt pilot lamp like a #47 or #755.

    73
     
    Shadetree Mechanic likes this.
  5. dozerman

    dozerman hello, its me again

    Joined:
    Dec 16, 2013
    Messages:
    185
    Likes Received:
    29
    i had the little green 2 tube contex a long time ago. i had the manual with it. best i remember, it tunes to peak and thats it. the light in the front is a tuning indicator. the brighter it gets, the better tune it has. atleast thats how my context was. it think mine had jg6's in it.
     
    Shadetree Mechanic likes this.
  6. nomadradio

    nomadradio Analog Retentive

    Joined:
    Apr 3, 2005
    Messages:
    1,788
    Likes Received:
    1,194
    The tuning lights were kinda cool. If you didn't have a meter in line you could still peak the thing.

    This one is wired to pin 5 of the nearest tube socket. Heater on this tube is at pins 4 and 5.

    73
     
    Shadetree Mechanic likes this.
  7. jessejamesdallas

    jessejamesdallas Sr. Member

    Joined:
    Apr 4, 2005
    Messages:
    1,158
    Likes Received:
    421
    AM only? no SSB delay...so sad.
     
    Shadetree Mechanic likes this.
  8. nomadradio

    nomadradio Analog Retentive

    Joined:
    Apr 3, 2005
    Messages:
    1,788
    Likes Received:
    1,194
    Doesn't have any fixed grid-bias voltage on the tubes. The tubes will tend to draw excess current with a low drive carrier level, or on sideband where there is no carrier.

    The carrier from the radio serves to set the tubes' operating current. With zero bias, they will cherry up and smoke something.

    The SSB switch on a lot of older sweep-tube amplifiers is a borderline fraud to begin with. Could easily be labeled "Suicide Selector".

    73
     
    Shadetree Mechanic likes this.
  9. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

    Joined:
    Oct 23, 2017
    Messages:
    772
    Likes Received:
    473
    I will double check what bulb is in it, I plan on pulling the cover back off so I can study it some more. So this light should be lit the whole time the unit is powered up? Sorry for the Noob Questions, Thanks!
     
  10. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

    Joined:
    Oct 23, 2017
    Messages:
    772
    Likes Received:
    473
    I think I saw one of those on eBay too. That would be a neat little amp to have.
     
  11. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

    Joined:
    Oct 23, 2017
    Messages:
    772
    Likes Received:
    473
    The heater on the 6LQ6 is pins 4 and 5. Taking notes. I learned transistors In tec school but they didn't teach us tubes. I will have to find out what the plate and the grid are all about. Thanks.
     
  12. dozerman

    dozerman hello, its me again

    Joined:
    Dec 16, 2013
    Messages:
    185
    Likes Received:
    29

    it was. a splatter box for sure. no fan so after a while of ratchet jawing, you could fry eggs on the cover. wish i still had that thing
     
  13. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

    Joined:
    Oct 23, 2017
    Messages:
    772
    Likes Received:
    473
    I plan to run this on my AM rig (Sonar 2340) and it would be nice to have an SSB mode for when I get an SSB radio. Gives me an excuse to buy another amp. LOL
     
  14. dozerman

    dozerman hello, its me again

    Joined:
    Dec 16, 2013
    Messages:
    185
    Likes Received:
    29

    yeah thats what im doing too. i follow these tube amp posts closely. all the tube techs around my neck are gone or going, save one in memphis. i pester a few of the techs on here with questions.
     
    Shadetree Mechanic likes this.
  15. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

    Joined:
    Oct 23, 2017
    Messages:
    772
    Likes Received:
    473
    That's interesting to know that the bias is set with the carrier level. I plan on running this with a Sonar 2340 that has a 1.5w dead key swinging to 18w. Should I turn the dead key up a little so I don't kill the tubes?
     

: amp, tube, 6LQ6

Share This Page

  • About Us

    The WorldwideDX Radio Forum was originally established in 2001. We pride ourselves on welcoming Radio Hobby enthusiasts of all types, while offering unbiased, informative, and friendly discussion among the members. We are working every day to make sure our community is the best Radio Hobbyist's site.
  • Like us on Facebook

  • Premium VIP Member

    The management works very hard to make sure the community is running the best software, best designs, and all the other bells and whistles. Care to buy us a beer? We'd really appreciate it!

    Donate to us!