AL811H and 811 tuning supplement
Supplemental Tuning Instructions 10/05/2011
Please take time to read!
Occasionally, first-time amplifier owners have difficulty understanding manual tuning instructions. Reading all manual tuning steps and “dry practicing” (without actually transmitting) all manual tuning steps will make initial operation much easier and safer.
We wish amplifier-tuning instructions could be shorter. Unfortunately, every step is necessary for proper amplifier operation, and we have carefully removed all unnecessary steps. This procedure omits as much as can possibly be omitted and still properly tune the amplifier. Some previous supplemental procedures issued do NOT properly tune the amplifier. Previous supplemental instructions can result in re-tuning when it is not necessary. Previous supplemental instructions also result in improper tuning, that while increasing tube life, also increase splatter.
Short of using a tuning pulser, there is no easy correct two-step or three-step tuning process. Tuning takes some practice but is something we must learn if we want good amplifier life and a clean signal. Eventually tuning becomes easy.
Easiest Possible Tuning Steps with Tuning Pulser
Make sure the pulser has the shortest possible pulse duration or “weight” for your radio. If you use dots on a keyer, make sure weight is 35% or less if possible. The shortest possible pulse is one that is just longer than the value that reduces peak output power. It is not necessary to use any special ratio of on-time to off-time in the pulser, perhaps as an attempt to simulate relative duty-cycle of voice modulation. It is also not necessary, nor is it generally advantageous, to use an audio injected pulsed tone. The only duty-cycle requirement is the exciter reach full peak power. Use the shortest possible pulse that allows full power. CW pulsers and audio-injected pulsers are equal in results.
Note: Do not attempt to force amplifier meters to these values on SSB voice, or pulsed tuning conditions. These are maximum currents shown accurately by meters only in steady carrier modes, although any carrier should be brief.
Easiest Possible Tuning Steps using a closed CW key, FM (push to talk), or AM (push to talk) Tuning
Note: Do not attempt to force amplifier meters to this value on SSB voice or under tuning-pulser conditions.
As a final adjustment, moving the LOAD control very slightly clockwise of maximum produces a cleaner SSB signal. Move the LOAD no more than ½ of a number position clockwise. It also helps to reduce the transceiver’s power a few watts from tune power.
The amplifier’s meters are not fast enough to follow SSB voice (or normal Morse code) signals. Never increase the transceiver’s power after tuning the amplifier to make amplifier meters go higher. The transceiver power control setting used in the last tuning procedure adjustment must be the same or less for normal operation.
A good, accurate peak meter will show a voice RF outputs about 10-20% higher than obtained with FM, RTTY, or CW carrier tuning methods. This is because amplifier high voltage on voice is closer to no-load voltage.
Depending on your voice and the amount of speech compression or ALC you use, amplifier front-panel meters will indicate about 1/5 to 1/2 of actual peak current. This is also true with average reading RF wattmeters.
There are two types of RF power, average power and peak envelope power. Both average and peak powers are envelope power, although we rarely hear the term average envelope power. Average power is the longer time average of envelope power, while PEP or peak envelope power, is the highest short-term peak of envelope power.
There is no such thing as “RMS power”. Audio marketing people created RMS power, along with other useless fictitious power types.
RF wattmeters reading true peak envelope power (PEP) generally require a power source of some kind to make the peak system work. Cheap PEP wattmeters often show only 50% of actual PEP when operating voice SSB. If a PEP meter is working properly, the meter will show more power on SSB voice than a steady, clean whistle or CW carrier indicates. The AWM-30 Ameritron is a very good peak reading meter, as are meters in Ameritron tuners. Many other meters do not accurately read peak envelope power.
Cheap or poorly designed RF power meters may read half or less of actual PEP on SSB voice.
Normally the amplifier will match up to a 2:1 VSWR or higher. You must use an external tuner between the antenna and the amplifier if your antenna’s VSWR is too high for proper amplifier loading. When tuning or operating the amplifier, be sure VSWR does not change. Do not use your transceiver’s internal tuner when using an amplifier.
ALC Adjustment and Operation
Never use ALC as a primary power control. The ALC control is another way to reduce the transceiver's output power. Unless connected to the radio, ALC has no effect.
Increasing the transceiver’s power control beyond this set point should not increase meter readings on the amplifier. This will verify the ALC is controlling the transceiver. We do not recommend depending on simple basic ALC systems for operating power control. It is only a safety measure.
2012-03-21 new rev 1 (clarified some wording)