AL-80 Hi Voltage problem.

[AC2FO]

Hello Have a al-80 when I turn it on the plate volts normally go up to 2500 volts, but now it seems the meter is pegged in the corner. I turned the amp on it's side and the volts went back to 2500, if I sit it as normal it reads plate volts in the corner, twist the chassis/frame the voltage goes back to down 2500. Poked around a little bit didnt see, loose, burnt etc. Fuse has blown a few times, this isn't my amp I am trying to get it working for a fellow ham. Obviously it sounds like a HV problem but where would be a good place to assume the problem lies. Diodes, transformer? HV Caps, metering circuit? Thanks for any help. Other than that amp see to work fine.

[KE3WD]

Bad connection to ground somewhere is the first suspect. Likely in the meter shunt circuit. Looking for it is dangerous to the uninitiated and could prove fatal. In other words, don't go poking around in there unless you know what you are doing and have experience troubleshooting less lethal equipments.

73

[W8JI]

I answered this in the other forum.

[KC7QNM]

UNPLUG AND put meter select Plate Volt Position, MAKE SURE NO METER INDICATES ANY ...0 VOLTS ...NO meter reading..DO NOT REMOVE COVER UNLESS PLATE VOLTS HAVE BEEN ALLOWED to DRAIN FLAT! Remove cover, Do not trust as the power supply can kill you and Packs A BITE . A shorting tool is made with a 6 ohm ,2 watt resistor and a plastic handled screwdriver. Resistor protect's componets from damage (1n4005 diode, Look at left side of amplifer outer edge of board above filter caps)..notice the most foward post that is the hold down hardware ...At the BASE OF and attached is the dark wire from the meter board going to ground ...Tighten the screws on underside of amplifer.. As the filter mounting componets also are ground mounting for METER CIRCUT GROUND WIRE. A good job of tightening the large screws on power supply filter board and the hardware used has repaired same meter issue on my AL 80A..

[KM1H]

The 2500V is too low to start with. The likely causes are leaky filter caps placing a heavy load on the transformer or the transformer itself has shorted turns which is rather common. I just finished rebuilding one with a toasted transformer for a customer.

Remove the HV leads (2 red ones) from the PS board and try again, if the fuse blows you know the answer. If not measure the voltage and see if it computes to the correct DC.

Ameritron sells the AL-80B transformer with a cheat sheet to do the swap. One error is that the new xfmr has a 24V winding and the 80A uses 12V. Rewire with just one yellow wire and the Black/yellow stripe one, tape up the other yellow.

Carl

[W8JI]

The 2500 volts could NEVER come from power supply loading, bad diodes, or anything like that. If it did, something would be on fire. The only possibilitly to be electrolytics would be if they have opened or gone really low in capacitance. In that case the amp would hum and have extremely poor regulation.

Ameritron does not have a transformer that fits the AL80.

The AL80 should be nominally around 2700-2800 volts. The small error to 2500 is most likely the fact the meter multipliers are 30 years old, especially if they came from a "transition unit" prior to Prime's ownership.

On units built by Amp Supply or that had parts bought them, many parts were surplus. Where ever they got the resistors used in the multipliers, I think Electronics Surplus in Cleveland, they were very unreliable.

Units after SN300 had all new parts and different wiring.

His problem sounds like a loose spacer, a bad meter switch, or perhaps a bad multiplier resistor. What to look at really depends heavily on the AL80 serial number.

73 Tom

[KM1H]

The 2500 volts could NEVER come from power supply loading, bad diodes, or anything like that. If it did, something would be on fire. The only possibilitly to be electrolytics would be if they have opened or gone really low in capacitance. In that case the amp would hum and have extremely poor regulation.

It blows fuses

Ameritron does not have a transformer that fits the AL80.

My fault, I see few of those early models and always think 80A was meant.

The AL80 should be nominally around 2700-2800 volts.

Yes its a rather different amp than the later ones and many of the early production were updated by Ameritron or elsewhere to correct design problems.

Carl

[AC2FO]

I answered this in the other forum.

Thanks Tom

[AC2FO]

UNPLUG AND put meter select Plate Volt Position, MAKE SURE NO METER INDICATES ANY ...0 VOLTS ...NO meter reading..DO NOT REMOVE COVER UNLESS PLATE VOLTS HAVE BEEN ALLOWED to DRAIN FLAT! Remove cover, Do not trust as the power supply can kill you and Packs A BITE . A shorting tool is made with a 6 ohm ,2 watt resistor and a plastic handled screwdriver. Resistor protect's componets from damage (1n4005 diode, Look at left side of amplifer outer edge of board above filter caps)..notice the most foward post that is the hold down hardware ...At the BASE OF and attached is the dark wire from the meter board going to ground ...Tighten the screws on underside of amplifer.. As the filter mounting componets also are ground mounting for METER CIRCUT GROUND WIRE. A good job of tightening the large screws on power supply filter board and the hardware used has repaired same meter issue on my AL 80A..

The 2500 volts could NEVER come from power supply loading, bad diodes, or anything like that. If it did, something would be on fire. The only possibilitly to be electrolytics would be if they have opened or gone really low in capacitance. In that case the amp would hum and have extremely poor regulation.

Ameritron does not have a transformer that fits the AL80.

The AL80 should be nominally around 2700-2800 volts. The small error to 2500 is most likely the fact the meter multipliers are 30 years old, especially if they came from a "transition unit" prior to Prime's ownership.

On units built by Amp Supply or that had parts bought them, many parts were surplus. Where ever they got the resistors used in the multipliers, I think Electronics Surplus in Cleveland, they were very unreliable.

Units after SN300 had all new parts and different wiring.

His problem sounds like a loose spacer, a bad meter switch, or perhaps a bad multiplier resistor. What to look at really depends heavily on the AL80 serial number.

73 Tom

Replaced the filter caps as well as tightend the spacers and it works like a champ. I suspect the poor grounding problem because when the chassis was moved or twisted the volts would read correctly. But the caps were the old silver can type so I replaced them.

Thanks for all that have replied, I value all your opinions and the ideas for a fix will get copied to a file for future repair use. You dont find this type of knowledge in the manual.

[W8JI]

Replaced the filter caps as well as tightend the spacers and it works like a champ. I suspect the poor grounding problem because when the chassis was moved or twisted the volts would read correctly. But the caps were the old silver can type so I replaced them.

Thanks for all that have replied, I value all your opinions and the ideas for a fix will get copied to a file for future repair use. You dont find this type of knowledge in the manual.

You never gave the serial number, and that is critical with the AL80. There are several mods that MUST be done if you want long service life for some serial numbers. If you amp is in the 300's or above, it has all the mods. The units of concern are the "Twinsburg engineered" amps under SN 300.