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I've obviously hit a streak...

Discussion in 'CB and Export Equipment and Accessories' started by 144inBama, Feb 5, 2021.

  1. 144inBama

    144inBama Electricity doesn't kill you, ignorance does.

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    Yesterday morning, (or possibly the night before) I blew a transistor on my Donkey Stomper 1X4. Apparently, SSB is a real killer on this type of amp, especially when driving it with 40 watts. I spoke with Chad and will be sending it back to him Monday and having bias added. It has the "delay" but as you know, that's just to keep the relay from chattering. From my understanding, biasing keeps voltage on the transistors at all times, but why is that important in SSB? And would switched biasing be ideal since I am on AM more than SSB most of the time?


     

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  2. S&W357

    S&W357 $upporting Member N.C. WDX-556

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    Yikes...sorry for your problem. Hope you get some good answers. :barefoot:
     
    144inBama likes this.
  3. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Yes, most Amps from years ago used to offer that, at least ones worth their salts...

    The current ones seem to want you to pop open the hood and install or remove jumpers as you make the choices on what you want the amp to do. (RM-Italy)

    Kinda' takes away the fun of why you have such a "delay" feature in the first place.

    But, in most cases - the Switched applies the voltage all the time - yes, but its; supposed to provide only enough to allow SSB signals to get thru that "knee" of Bias that makes a typical Class C amp sound "crunchy" in SSB modes.

    And can blow up those Amps due to their dynamics in both signal and it's volume range...(PEP level and RMS Level of Compression voice applies to the RF side of the SSB signal - it's the Drive).

    So only use Bias when in SSB or as needed.

    For Swing modes in AM that would otherwise chatter the signal from the Relay cutting in and out. Just Use The Relay Delay - else AM signals provide a lot of power in their Carrier - if you apply BIAS to the amp at the same time - the Amp will certainly operate LINEARLY and possibly Clip (Fuzz-up Pinching Audio) because your amps new bias is ADDING power to be amplified (the lengths of ON-time in the RF cycle is NOW LONGER DURATION OF TIME) right at the base of the transistor - DIRECTLY.
    • - sure its' DC but hey, it turns on at lower level signals now because of it
    • - so it takes in a lot more signal and CONSUMES a LOT more power in it's output.
      • Read this as HEAT production - Power Yes, Clean Yes, but LOTS MORE HEAT
    • May not be what you want to see - but it does...

    Hope this picture can speak the volumes I would otherwise have to post...
    upload_2021-2-5_10-59-18.png


    The choice to go AB in SSB is great, you will sound better but that amp can't run like that all the time - so when in AM (Or FM) - run Class C...

    In both cases - SSB needs ALC to work, to keep it's PEP output from the Radio below the Critical Warp Core Breech in progress moment...

    upload_2021-2-5_11-4-30.png
    I see this in the back of my mind lots of times -
    Fixed a lot of them due to the Operators not remembering to turn off SSB mode​

    Same thing for the AMC on AM - you don't want to overdrive the amp with OverSwing the radio will try to put thru that amp. Too much of a good thing - usually is...See Above...
     
  4. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    Andy is right on top of this one.

    I also want to note that 40W peak is way too much input for a 1 x 4. That configuration runs best with a single final radio at ~20W peak output, no more. Anything beyond that can cook the driver transistor, or can overdrive the 4 transistors and cook one of them, or take out both the driver and a final transistor.

    When you get it back, I highly recommend running 20W peak max into the amp for prolonged life and cleaner output. Having proper SSB biasing on the transistors will help with cleaner output also.

    ~Cheers~
     
  5. AudioShockwav

    AudioShockwav Extraterrestrial Admin
    Staff Member

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    What he said above.


    73
    Jeff
     
    144inBama and Slowmover like this.
  6. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Anyone ever modulate the output transformer ferrites with a rattling that sounds like talk back? :whistle:
     
  7. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    There was a guy that was local to me years ago, that ran a "comp" 4 pill, when he'd modulate through it, you could see the ferrites on the output transformers actually rotate counter-clockwise. It was the most insane thing I'd ever seen, and I remember it to this day. Couldn't even imagine how much saturation those output transformers were experiencing! It kind of defied the laws of physics in a way, but I saw it with my own eyes.


    ~Cheers~
     
  8. Dmans

    Dmans Sr. Member

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    If it were mine, I would change the "SSB/Delay" switch to add another pole that trips a relay to add bias when in SSB only.And only drive it with 20 watts peak or remove the driver and make it a straight 4 pill.

    73
    David
     
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  9. Onelasttime

    Onelasttime Sr. Member

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    Yes class C biasing is to a transistor what running a John Deere 2 cylinder is with out a flywheel is and attempting to put a load on the engine!

    This is why I have always thought it was criminal or the same as having an IQ bellow 73 to even build and sell an amplifier on the market with out at the minimum class B biasing and delay. All ham HF rigs have SSB and a good many CB radio's do as well. The only person a class C amplifier is fit for is someone that likes to key up and say "AUDIOOOOOOOO" or play 1970's hard rock on the radio in a drunken stupor. Oh and those idiots on channel 6!

    For the record I have been known to get on the internet drunk or under the influence of sleeping pills but never the radio! Some things are sacred! LOL......

    Oh now I am all good for an amp with variable biasing that selects it's bias based on radio mode.

    Just like I love the idiotic idea of driving 4 transistors with 2 like or similar output transistors! LOL Mo-Pow-Aw.....LOL
     
  10. Onelasttime

    Onelasttime Sr. Member

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    We learn sooner or latter. I am glad I had a mentor to set me straight in high school!
     
    144inBama likes this.
  11. 144inBama

    144inBama Electricity doesn't kill you, ignorance does.

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  12. nomadradio

    nomadradio Analog Retentive

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    I tell folks using AM linears for sideband to expect half or two-thirds the peak power they see on AM.

    If they want to sound right. AM forgives overdriving an amplifier much more than sideband.

    Cutting the radio's drive level in half or less tends to improve the audio quality in a big way.

    Then again, if the radio's limiter is cut for sideband, reducing the drive level will make it sound better barefoot.

    If a radio delivers forty Watt peaks on AM and the sideband limiter is cut, the 'wide open' average sideband power could be over thirty Watts. Try turning up the AM carrier to 30 Watts and see how long it takes the amplifier to pop.

    The radio really needs that limiter for sideband, even if you cut it loose for AM only. Average wattmeter readings might seem disappointing, but sideband audio just does not forgive overdriving.

    Sideband is the "Turn the wattmeter to face away" mode.

    73
     
  13. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Looks good to me too, I like how he is using the small relay to switch both the delay and the bias power. Clean straight forward design. I have an XForce 4 pill that has the bias power going through the keying relay with some extra coils and caps for isolation. I dont know why they went through the trouble to do it that way. Enjoy!
     
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  14. 144inBama

    144inBama Electricity doesn't kill you, ignorance does.

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    I've never had a complaint about how the radio sounds on SSB, only compliments....except for 2 times when I'd forgotten I had the echo on....one guy up north instantly "diagnosed" the cause of the offending noise, turned the echo off and all was right in the SSB realm again (BTW, echo on SSB seems to almost be punishable by death). I'm doing 40 watts AM and around 30-35 SSB. I don't think anything has been clipped, but I don't want to break his seal to check either. Using a monitor radio, it sounds crisp and clear, it doesn't have that...."crunchy"(?) or "tinny" sound to it like most radios I've heard with the clipped/cut super dooper mods. I'd like to see if he can add a Hi/Lo power switch, maybe where the OFF/SWR/RB switch is, with low around 20 watts or so in hopes of lowering the abuse on SSB.
     
    Shadetree Mechanic likes this.
  15. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    On sideband, I would run on high power. Then use mic level to adjust power out.
     

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