AL80B AL572 AL800 AL800H Correction Kit (AL8X Kit)

Note: I also have AL80 and AL80A/SB1000 parts.

I designed the AL80B and other AL8X frame amplifiers in the early 1990s. These amplifiers have a long history of reliable service but could still use updates. The AL8X kit contains all parts required to correct and update the AL8X frame amplifiers, which include the AL800, AL800H, AL572, and AL80B amplifiers.

See this link for the latest update details on the AL572, AL80B, AL800H and AL800

This kit supplies all the parts required for any generation of this amplifier. This kit is $25 shipped to any USA postal system address.

Kit contents:

  1. one 1N4739A 9.1V 1-watt Zener (EBS correction)
  2. one 2.2K resistor (relay keying correction)
  3. one 1N752A 5.6V Zener (relay keying threshold correction)
  4. one .33uF to .47uF timing capacitor to replace C152 (C52)
  5. two 1N5335B 3.9V 5W low voltage supply correction diodes
  6. two 1N5408 meter protection diodes
  7. braiding for ground grids in some early AL572
  8. two 230V GDTs for tube filaments
  9. PTC fuse for 12V aux line to replace 10-ohm fuse resistor

Warning! If your amplifier has pink colored bleeder resistors, they should be replaced. The pink resistors were pulled from production because of high failure rates. When a resistor fails, it takes out all of the filter capacitors. MFJ, when they ran out of good resistors, started using the bad resistors again. This means any year might have the old defective resistors.  If you need these resistors we can supply reliable substitutes. Regardless of the replacement source, you must change the 50K 7 watt pink-color bleeder resistors out.

Parts ORDERS or parts questions go to

About This Kit
This kit’s corrections include:

(For units with small enclosed relays, rather than large open frame relays)
1.) Restoring relay operating time from the current 20-30mS closure time to time<8mS (by removing C152)
2.) Correcting relay sequencing errors
3.) Correcting relay line impedance sensitivity, which cause premature loss of receive

(for later production year units after a transformer vendor change)

4.) Correcting grossly excessive 12Vdc line voltages, which damage the metering op-amp. This was caused by a transformer ordering error

(for all units of all years)

5.) Improvements to the auto-bias circuit
6.) GDTs to improve radio and amplifier protection in the event of a tube arc

I strongly suggest owners of the AL80B, AL800, AL800H, and AL572 read this link:

AL80B AL800 AL572 Link to Updates and Error Corrections

About the AL80 History

I was responsible for the AL80 series starting in 1983 until MFJ took over. The first AL80 was a Twinsburg design Prime Instruments inherited. Ameritron-Prime recalled all known AL80s and remanufactured them to Ameritron-Prime standards. Remanufactured units were assigned S/N 300 and up. Revised new units were S/N 500 and up.

The larger and higher-performance AL-80A was the first full Prime design, replacing the AL-80 in the mid-1980s. I sold the kit rights, with some modifications, to Heathkit as an SB1000.

The AL80A ran until replaced by the AL-80B. The AL80B frame and main circuit board, with a different transformer, were also used in the AL-572, AL-800, and AL-800H.

The AL80B had a larger transformer and more features than earlier AL80 amplifiers, including true peak-reading directional coupler wattmeters and a very special design ALC circuit. The AL80B and other amplifiers in this mainframe, including the AL572, AL800, and AL800H all have grid current derived ALC. The Ameritron solid state amplifiers and the AL80B style mainframes are the only amplifiers I almost insist on being used.

Unfortunately, once designs were turned over to MFJ pretty much anyone, whether they understood circuit function or not, would randomly change things. Instead of improving reliability and performance over the years, which is the normal direction designs should go, amplifiers deteriorated.