Ameritron 811 and 811H Upgrade Kits

Link to pdf file 811KP (protection) and 811KS (supply) instructions:

AL811 and AL811H Upgrade Kit Manual (Rev2)

These kits include all the parts to bring your Ameritron AL811 and AL811H amplifier up to date. We also sell quality 572B, 811A, and 3-500 tubes  and almost any other RF parts you might need.

The following is a list of critical production problems:

Inadequate Cooling


Instructions for fan replacement kit:

Fan Mod AL811 AL811H (Rev 1) PDF file

Warning: All AL811 and 811H amplifiers sold with the pictured Cooltron fan have far too little airflow. Measured airflow is about 1/2 to 1/3 of required safe airflow for four 811 tubes in normal SSB and CW operation. With this fan, internal temperatures will have two to three times the safe thermal rise.

We offer a drop-in 12Vdc fan kit that flows adequate air for normal amplifier use.

This is the recent very bad fan, but not the only weak fan they used. Proper airflow results in a noticeable air movement a foot or so away from the vent holes by the tube. A crude test is a BIC lighter should blow out about a foot away from the vents:

Bad Ameritron/MFJ Fan

This fan must be replaced!

Fan Kit AL811 and AL811H Fan Kit page

AL811H AL811 Ameritron Parasitic Suppressor System


Instructions for installing parasitic suppressor board:

AL811 AL811H TPS3 TPS4 parasitic suppressor upgrade instructions pdf file

The original tuned suppressor is supposed to be 5-turns wound on a .375″ rod, spread to hole distances. There is also supposed to be a thick washer under the board to prevent shorting the 100pF resistor resonating capacitors near the choke. The resistor is supposed to be a known internal inductance, not non-inductive.

This suppressor was developed when non-inductive resistors were in a shortage, but it does have superior performance when built correctly.

See this link for operation of suppressors:

The CTR Engineering TPS4 for 811H and TPS3 for AL811 are vastly improved layouts that reduced chances of shorts from incorrect hardware. These boards provide more reliable parasitic suppression and are less critical for mounting.

This system measures to be vastly superior to hairpins and a much better layout than the OEM Ameritron parasitic board. The TPS3/TPS4 system has faster resistance slope with increasing frequency, and more suppressor series equivalent resistance at 811 problem frequencies of just below the FM broadcast band and 225MHz.

TPS4AC full with anode connectors $41.95
TPS3AC full board with anode connector $34.50


Ameritron Parasitic Suppressor 811 Amplifier

Comparison to stock board, bottom view OEM on left, CTR right

Note how easy it is for the MFJ factory board (on the left) to accidentally short some of the 100pF capacitors when the proper choke stacking spacer is accidentally left out. The TPS3/4 AL811 amplifier parasitic suppressor boards have a large pad and attached spacer greatly reducing or eliminating the accidental short so common at the choke top. A shorted capacitor will almost quadruple resistor heat on ten and fifteen meters. Our board also has heat dissipating pads and moves the resistors apart.

AL811H Parasitic Suppressor Board replacement

Improved AL811 Ameritron Parasitic Suppressor Top View OEM left, CTR right

This is the correct inductor and resistor layout. The resistors, which are the correct style resistors, also have heat spreaders on the circuit board. This board has more than enough suppression series resistance on critical frequencies but less resistance on ten meters, where we do not want any resistance.

811KS Power Supply kit $49 plus shipping Order now

(Power Supply rebuild kit)

1.) four better capacitance size much longer life 105c rated 500Vdc electrolytics
2.) four new bleeder/equalizer resistors
3.) one large 6A grid and plate meter HV fault protection diode to replace small OEM diode (or keep as spare)
4.) two or four meter HV scale multiplier resistors. These resistors also correct a slight meter error, depending on parts supply chain issues, you may get two 1M 1kv rated resistor or four 499.9k 1kV rated resistors

811 amplifier power supply

Ameritron AL811 Power Supply Upgrade Kit

811KP $29.95 plus shipping Order now

(Protection Kit) 811KP
1.) three application tested GDT tubes
2.) one large 6A meter protection diode to replace the small OEM diode (or keep as spare)
3.) one 100k 2-watt resistor
4.) two 3.9V 5-watt Zener diodes to reduce tube heat
5.) 10-ohm 9-watt CCS 10,000 volt rated fault resistor to reduce arc currents

AL811 protection GDT kit

Amplifier GDT Protection Kit

Add on:
811R200K $18 plus shipping Order now

200-ohm 25-watt non-inductive load resistor, ceramic capacitor, with all necessary stainless hardware for Ameritron AL811 amplifier. This more closely matches AL811 drive power to 100W rigs like the ICOM IC7300, reducing overshoot issues, improving IMD, and increasing stability. All AL811 amplifiers were supposed to have this resistor from the factory. If you have a rig with overshoot issues, like the ICOMM 7300, it is a good idea even in the AL811H.

AL811 200 Ohm resistor kit