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Thread: modulation pots

  1. #21
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    Triple deuce you are a godsend! Thanks for your insight and more importantly your patience!!!
    Gasman

  2. #22
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    No worries man, I will try to help as much as I can!! I am no expert, but do dabble a bit! I am stepping my game up as I go along. Next up, ICOM 7200 a real HF radio. Can't wait!! But anyway again no worries ask away! Have a great one and god bless.

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    gasman (07-11-2014)

  4. #23
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    Ok. Checked swr. Ch 1 dead key is 1. Channel 20 also is at 1. Channel 40 is 1.1. This is with both the cobra and connex. I know it shouldn't change between radios and it didn't so that's good. Cobra mic gain was turned all the way up. With this new meter dead key is 2w swings to 6w on ch 1, 8w on ch 20 and 10w on ch 40. Is this normal? Connex with mic gain @ 1 o'clock is also 2w. Swings to 20w on ch 1, 25w on channel 20 and 30w on ch 40. Again, normal? Now for the 2 golden questions: 1. When speaking into the mic the swr needle swings, is this indicating the ref power? And 2. My Palomar 225, if I use my connex on this amp do I need to cut the power off in order to not burn it up? We'll start with this and maybe later we can get into why high voltage can't hear me on the cobra with the amp on at a stones throw away. Thanks.
    Last edited by gasman; 07-12-2014 at 03:50 PM.
    Gasman

  5. #24
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    modulation pots

    To properly check swr, turn mic gain all the way down, no modulation. Calibrate meter and take readings. Your dead key on the radio should be around 3-4 watts , mic gain all the way down. And don't worry about the needle moving while taking, that is normal, like I said, swr readings require that no modulation be used. Only a carrier. Your dead key should be above 2 watts, 3-4 watts dead key is normally what is needed. Check the specs on the meter you have. If possible look at the directions or google it and try to find some directions. Here is a page about checking swr as well. http://www.cbtricks.com/members/toban/swr.htm
    And yes for that amp, you want the amp to have a 1:4 ratio carrier. So if the amps total output is 200 watts, you want the amp to have a carrier of 50 watts. These amps don't require much dead key, normally between 1-2 watts and pep of 12-15 watts is about max. I would keep using the cobra 25 with it and get your dead key down to 1-2 watts. This can be done with a cap and resistor mod or a TIP120 mod. Check out Cbtricks for more info as well. Good place to get info for the 2 radios you have. Hope this helps and god bless.
    Last edited by 222DBFL; 07-12-2014 at 06:00 PM.

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    gasman (07-15-2014)

  7. #25
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    Hello again. So I went to the Sussex ham fest and I purchased a Texas star 250hdv. I did a temp hook up to check it out. It powers up, pre amp works but I am not seeing any power increase on my meter on tx. The meter built into the amp does not move either. Did I do something wrong or did I get goonched? Is there any way I can check the 2 2289 finals with a multi meter and if so am I looking for dc voltage or ohms?
    Last edited by gasman; 07-15-2014 at 03:31 PM.
    Gasman

  8. #26
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    You need an external swr/watt meter. Radio shack has a decent one for mobile use. And make sure the radio you are using has the am carrier set to 1-2 watts max. Do not stick a volt meter in that box, you can burn the transistors. They need to be taken out to be tested properly. But first if would get a watt meter and place it in line after the amp. So it will go, radio to amp, amp to watt meter, watt meter to antenna. And what radio are you using? What is the dead key set to? I would not run more than 2-3 watts dead key into that amp. You want the amp to key up at about 1/4 the total output. So a 250 watt amp would key up around 50-60 watts. Then let it swing from there. Use a single final radio as well and the amp will last a very long time. Over driving the amp will send it to the grave early. But anyway. Check all these things and if in doubt send the radio and amp to a good tech and have them match the radio and amp. This way it will definitely work properly. Have a great one and god bless.

  9. #27
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    I used an astatic 600 swr/power/modulation meter hooked up as specified. Running my connex 3300hp with power turned all the way down its 2w d.k. This was how I checked the amp. I seemed to get nothing out of it. I will hook it up properly when it stops raining and try again.
    Gasman

  10. #28
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    Does the amp have a variable knob or is it the button type. The variable knob is a weak point on those amps. How much you have in it? Might be worth it to send it off to a good tech.

  11. #29
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    Yes it is a variable power amp. Bought it Sunday for $80. Any ideas how to tell if it's the v control? I'm pretty confident I could change that myself. The issue I have is trouble shooting the thing. I can read a diagram/schematic, can even find info on the part specifics. Just not sure where to start. If only I knew the sequence of operation and what parameters to check the specific components for.
    Gasman

  12. #30
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    Is the variable power device like a potentiometer? Can I just jump it out to check it or will I fry everything? I know once you let the smoke out, no matter how hard you try, you're never able to put it back in.
    Gasman

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