Callsign
ad: radiowavz
Results 1 to 4 of 4

Thread: sb200 problem

ad: L-HROutlet
ad: l-assoc
ad: l-Waters
ad: l-rl
ad: l-AmericanRadio
ad: l-innov
ad: l-gcopper
ad: l-BCInc
ad: l-tentec
  1. #1

    Default sb200 problem

    I bought a used sb200 and I have a problem with very low output.
    I have good hv shown on the meter
    both tubes filiments light up.
    with the amp off rf passes through easily and the built in swr meter works
    when you turn the amp on the exciter sees swr at infinity, only tried on 40 meters.
    using the exciters built in automaticd tuner will correct the missmatch.
    driving with at least 60 watts I get almost no output. tune and load controls do seem to work. plate current is very low and grid current is too low for the meter to read. I have cleaned the tr relay and input band switch that was no help. Can the tubes be so bad that all this happens? I use an external relay to protect the ts2000. I do not have the alc connected. the unit is running on 230vac.
    there are no known mods to the amp.

  2. #2

    Default

    Clean the bandswitch including the input and output to the amplifier.

    Check the actual antenna changeover relay in the amplifier and make sure that when it is in the engaged position that the input from the exciter is actually connected to the 572B tube input circuit.

    If you end up "giving up" on the linear, bring it up to Richardson to me.

    Glen, K9STH

  3. #3
    Join Date
    Oct 2003
    Location
    Middle Georgia USA
    Posts
    7,722

    Default

    Quote Originally Posted by WB5OXQ View Post
    I bought a used sb200 and I have a problem with very low output.
    I have good hv shown on the meter
    both tubes filiments light up.
    with the amp off rf passes through easily and the built in swr meter works
    when you turn the amp on the exciter sees swr at infinity, only tried on 40 meters.
    using the exciters built in automaticd tuner will correct the missmatch.
    Try more than one band, otherwise it is a toss up between bad tubes or a tuned input problem. If it acts up on all bands, it is probably tubes. It virtually 100% is NOT the relay by your descrition.

    driving with at least 60 watts I get almost no output. tune and load controls do seem to work. plate current is very low and grid current is too low for the meter to read.
    Could be tubes, could be bias, could be input circuit. Try more bands.

    I have cleaned the tr relay and input band switch that was no help.
    I don't understand why it is so common to clean relays. That's almost never a good thing to do for problems like high input SWR, and relays almost always are cleaned in a harmful way. The only time a linear amp relay needs cleaned is when the receive is erratic through the amplifier.
    Can the tubes be so bad that all this happens?
    Yes. Relays can't, but tubes can. Could be a bad tuned input on 40, could be bad bias components. Try more than one band.

    I use an external relay to protect the ts2000. I do not have the alc connected. the unit is running on 230vac.
    there are no known mods to the amp.
    Good.

    73 Tom

  4. #4

    Default

    Do you at least get idle current when in TX?

    Its a rare case when a tuned input causes zero output, its usually just very low output and a high input VSWR.

    Common SB-200 problems are arced bandswitches, open grid resistors and an open plate choke.

    Carl

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •