Help with Amplifer

This topic contains 6 replies, has 3 voices, and was last updated by  KU1V 1 year, 7 months ago.

Viewing 7 posts - 1 through 7 (of 7 total)
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  • #6613

    Ernest Swersky
    Participant

    I’m trying to connect an Ameritron AL-80A to my TS-850SAT. (I just got the relay cable today). When I follow the procedure specified in the instructions I’m unable to increase the grid current past 25mA. Increasing the power output of my radio has no effect. The amp keys with the radio and the XMT light comes on. Could this be a tube failure mode? I’m stuck.

    #6615

    Jeff Millar
    Participant

    Hi Brian…

    Is this a new or used amplifier?…sounds like used.  It may have a few quirks to work out.

    Low grid current could be…

    • input network problem limiting drive to tube
    •    bad bandswitch
    •    bad input network tuning
    • input match to amplifier limiting power output from the transceiver
    • excessive ALC limiting transceiver output
    • excessive plate load limiting plate voltage swing

    What’s going on with the plate current?  It should increase with increasing drive.

    What’s going on with the plate tuning?  There should be a distinct dip in the plate current when changing the tuning knob.  Do this test with the plate loading capacitor fully meshed (minimum load).

    Grid current is caused by the grid intercepting some of the electrons coming off the filament (cathode).  When the plate voltage is high, the electrons are pulled to the plate and grid current is low.  When the plate voltage is low, the electrons move more slowly and more get intercepted by the grid.

    At full load, the plate voltage swings from near zero to near 2X the DC supply voltage.  If it spends too much time near zero, the amplifier is lightly loaded and grid current soars.  If the amplifier is too heavily loaded, the plate voltage can’t develop enough swing, the minimum never gets near zero and the grid does not intercept too many electrons.

    jeff, wa1hco

     

    #6630

    Ernest Swersky
    Participant

    The radio was bought from Jahnke so I know it’s working properly.  The person from whom I bought the amp says it was working properly the day before he shipped it and I believe him.  I’m positive that my problem is an I D ten T problem as in ID10T.

    Well, it appears that the ALC was limiting the output.  I’m still stuck trying to tune the amp.  The instructions say to set the ALC on CW which, to my mind, makes no sense.  That’s just the beginning of my confusion.  What input do I use to set the amp, as in a tone, voice?  As an electrical genius I make a decent retired doctor.  Anyone wanna waste some time pointing me in the right direction?  I’m near Nashua High School North.

    #6636

    KU1V
    Participant

    Hey Brian,  To start I am somewhat tech challenged with most of these elec issues so use a few grains of salt with my experiences with tuning my Kenwood TL 922. I also use an al-80B with tuning similarity.

    As to tuning in CW I do not have an answer why, but seems when going to SSB from CW tuning, the amp may not be properly tuned. I received distortion complains from tuning in CW and was suggested to tune in SSB.

    Here is what I do,  make sure amp band and trans freq. match then select SSB.   Use load/output power meter in line.     Amp load/plate to known value or suggested per manual.    Drive 5-10 watts and key down. Watching output power move amp load control to max output — then adjust plate to max output.  Then increase drive and repeat for max power or until you have output power you want.

    I do watch Ig and Ip during initial operations for correct parameters, but always seem OK.

    Here is a link for tuning 922 and he does start in CW but finishes in SSB.

    73  Mike

    #6637

    KU1V
    Participant

    Brian, I should have added I have ICOM radio and use RTTY for drive while tuning amp.

    73 Mike

    #6638

    Ernest Swersky
    Participant

    Once I get past the first steps I’m supposed to increase the radio’s power from minimum to get a grid reading of 50mA.  That’s the point where the grid current doesn’t increase with an increase in power from the radio.  I’ve tried it with the ALC control at various levels and there is no change.

    Ernest

    KC1GIR

    #6639

    KU1V
    Participant

    I would disconnect the ALC

    Mike

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