Ameritron AL80B AL811H AL572 Amplifier Trouble Shooting

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Power line voltage jumpers in AL80B mainframe. This includes the AL572 and AL800 series.

E to F and 1,2,3 concern buck-boost, to fine adjust the voltages. The pictured setting is for 115/230 volts, without any buck or boost. These pictures ONLY concern the jumper wires. The board used for photo has no transformer connected to transformer pads.  






Supplemental Trouble Locating Hints


TROUBLE SHOOTING guide below generally applies to many types of amplifiers with suitable part number changes.

(In order of most common occurrence)


1.) Test on SSB using MOX or push-to-talk with no mic gain. With no RF drive power, but the amplifier keyed, the amplifier’s grid current meter deflects about the same as the plate current meter. This is a common problem

  • D16 shorted (811), D117 in AL80 series mainframe, including AL572. This will also cause the plate and grid current meter to track each other, and indicate false grid current
    • This problem is almost always from a defective tube or tubes that have flashed over internally, generally from excessive internal gas
    • This problem occurs after HV has been shorted, arced, or discharged to chassis
    • In older AL811H and AL572 amplifiers, grid circuits using resistors should be modified to current production

2.) Grid meter moves backward, and Ip meter reads forward, with no drive and amplifier in standby

  • Tube has a filament-grid short from shipping damage or tube manufacturing defects 
    • A shorted grid-filament shows as little or no RF output power, and high transceiver SWR
      • Try removing all tubes, then insert tubes one in at a time, to find bad tube
  • Tube has or had an internal arc from gas or air leakage
    • If a tube arced, a filament circuit component may have shorted to the chassis. This could be a MOV on the filament winding of the transformer, or a gas protection clamp tube under the sockets
    • A defective bypass capacitor may be shorting the filament or the filament center tap line to ground
  • A backwards moving grid meter that never goes forward is always an indication of a filament to ground shorts, either inside or outside the tube  

3.) Amplifier blows fuses when power switch is turned on (always use proper 250V fast-blow fuses), blows step-start in other amplifiers

  • Check for shorted tubes 
    • Remove the plug from outlet, remove the cover, and remove the top white anode connectors from all tubes. Do not let the white ceramic plate caps touch anything; lay them carefully on the tube glass. Replace the fuses and cover, plug the amplifier in, and turn the power on. If the amplifier powers up with tube plate caps disconnected, a tube is shorted
    • You can inspect the tubes for a silver area on the plate (sign of overheating), or reconnect tubes one at a time until the problem reoccurs to find the bad tube. Never connect the amplifier to power lines with the cover removed
    • If the problem is not tubes, defer service to someone experienced with high voltage circuits

4.) HV/Plate Current meter reads flakey, tapping or rocking switch while in Ip position makes meter jump around (AL811 series only)

  • Dirty contact in rocker switch
    • This is caused by switch manufacturer defects
      • Flood switch with WD40 and rock switch several times
      • If cleaning does not restore, replace switch

5.) Low Power Output

  • This is normally weak tubes, ALC, or improper tuning (see Tuning Supplement Sheet)
    • Normal RF power gain is about 12 times input power. If drive power is 40 watts, the AL811H should produce 400-500 watts into the antenna and 600-700 mA plate current
    • Weak tubes also often cause high input SWR on all or most bands
    • Grid current should normally be 1/3 of plate current when properly tuned near full output
  • Be sure your RF output meter is good (see Tuning Supplement Sheet)
    • Check your radio power through meter with amplifier off. Radio should be 100 watts using high power scale of meter

6.) Noise in receiver and/or erratic amplifier meter readings on standby

  • Bad tube or tubes
    • Test as in step 2, problem similar to step 2
  • Bad parasitic suppressor connection, resistor, or inadequate parasitic suppressor inductance, this illuminates gas tubes on filament transient suppressors       
    • This problem only occurs on some bands, with some PLATE control settings. It can be made to disappear by changing bands or PLATE settings.
    • Squeeze suppressor inductors turns closer to increase inductance
    • Ideal turns are now 6-7 turns for 811 tubes
  • Alter biasing system. This is a new mod effective Mar 21, 2012
  • Defective GDT (gas discharge tube) or defective MOV


7.) Audible popping noise and/or clicking noise

  • Faint sharp ticking, might show in receiver as noise 
    • open RF safety choke on loading capacitor allowing load cap to charge up and arc. Choke should be less than 40 ohms
  • Hollow louder muted click, might not appear in receiver       
    • Open bleeder/equalizer resistor across filter caps
    • Bad filter capacitor
    • Bad connection on filter cap area of power supply
  • Open or poorly soldered plate choke winding connection
  • Fan blade hitting something
    • Speeds or slows with fan

8.) No receive or weak receive

  • constant transmit light on amplifier
    • Unplug relay line from amplifier
    • If light goes out and receive restores, cable or radio connection bad
      •  If light remains on, problem inside amplifier
  • bad connection in antenna system, tuner, or feed line
    • try a different antenna system  to see if it restores receive
    • try moving cables or tuner switches to see if it restores receive
  • no transmit light on amplifier but still no or weak receive
    • Unplug relay line at amplifier
      • if receives, problem in radio or relay cable
    • Turn amplifier power switch off
      • if receives, problem in amplifier
    • Transmit through amplifier with amplifier power or standby switch off
      • if SWR high, remove amplifier and substitute double female barrel connector in place of amplifier. Make no other changes
        • if SWR now low, problem inside amplifier
      • if receive restored
        • bad or dirty relay in amp
        • bad or loose antenna system connection


9.) No or very little transmit power with amplifier on, OK on bypass

  • If amplifier transmit light does not light, short relay line to ground
    • If transmit light works, problem in radio or cable
    • If transmit light does not light, problem in amplifier
  • If amplifier transmit light lights but no transmit
    • High exciter SWR
      • Output and input cables reversed
      • Bad jumper cables
      • Bad tubes, also see step 5
    •  ALC too high or bad tubes. Also see steps 2 or 5
  • If grid current is very high and there is no plate current
    • No HV to tubes
    • If HV is normal on HV meter, open plate choke or plate supply wire to tubes
  • If plate current is very high, grid current very low, tank circuit problems
  • If plate current is very low, grid current very high, open blocking capacitor, or tank circuit connection open  

10.) VSWR goes intermittently high on the RF power output meter(s) when tuning

Plate or grid meters jump around with a steady carrier while VSWR changes

  • This is almost always some type of cable, antenna tuner, or antenna system problem

o     Try tuning the amplifier into a dummy load with any antenna tuner in bypass or direct

§      If the amplifier tunes up ok with the dummy load connected, you have a tuner, feed line or antenna problem

o     Change tuner output to a dummy load, and tune into the dummy load with amplifier in standby.  Now try the amplifier 

§      If the VSWR reads ok with the amplifier, you have an antenna system problem

§      Wiggle cables behind amplifier to see if connector or cable loose or bad

o     Check center pins of connectors to be sure poor soldering or bent pins have not ruined connectors

§      Too much solder on male pin will ruin female connector

§      Unsoldered male or improperly assembled male will cause poor connection

§      Some import cables and connectors are manufactured wrong size. Try different cable for better fit


11.) Transmitter or transceiver SWR too high through amplifier, should be under 1.5:1

  • Bypass SWR (amp on standby) also high, see step 9.
  • Bypass SWR low, SWR only high when amplifier on operate
    • Amplifier TUNE and LOAD improperly adjusted can slightly affect SWR
    • Incorrect band selected
    • Jumper cable between radio and amplifier defective
    • Remove switches or devices between amplifier and exciter. Be sure nothing other than a good coaxial cable is installed between amplifier and radio
    • Radio's internal antenna tuner should be off
    • Weak tubes cause a high input SWR on all or most bands. see 1, 2, and 5

12.) Grid meter pins with low drive power

  • No plate current
    • Open RF plate choke or no high voltage
  • Low plate current that does not change with tuning
    • Open tank circuit feed, open blocking capacitor
  • Normal plate current and output, but grid meter pins hard
    • Open grid shunt R8 1.5 ohm
      • Can be caused by filament to grid/ground short or tube forced in socket wrong
  •    Low RF power output
    • Loading control too far meshed, load capacitor shorted, or antenna system bad
  • Also see 1 and 2

13.) Amplifier does not appear to key, or does not release

  • Disconnect from the radio. Ground the center pin of the relay line to the amplifier.
    • If it works this way, you have a radio connection,  radio configuration, or radio component issue
    • If it doesn't work this way, try a new relay line
    • If the new relay line does not fix it, you probably have an amplifier problem




2011 Oct 07