Acom 1500 Manual page 13

Adjust amplifier tuning when you change the band or between CW and SSB segments within the same
band. Readjust it each time when you change the antenna, even in the same band, as well as
periodically, even though you may have not changed band or antenna. A significant change in the
environment, such as snow, ice, new or removed large metallic objects, alien wires nearby etc., can
cause significant changes in the antenna impedance and an increased VSWR.
If you use more than one antenna per band, it is necessary that you select the proper antenna
BEFORE the next step. Retune after selecting a different antenna for the same band, since the
impedances may differ substantially (unless their VSWRs are excellent, i.e., below 1.2:1 for
both).
Do not switch the BAND switch knob while transmitting with the amplifier! Such hot switching
will eventually destroy the band switch, and this is not covered by the warranty!
When tuning, do not apply continuous drive longer than 3 minutes and after that pause 1-2
minutes for tube cooling.
We recommend that you tune-up at the center frequencies of the preferred frequency band. First,
select the band switch and the correct antenna number (never with RF applied!). Then, use table 4-1
in order to achieve an approximate preset for both TUNE capacitor and LOAD capacitor knobs:
b) Selecting the plate-load True Resistance Indicator (TRI) tuning aid.
You may select the TRI scale in three different ways:
- By briefly pressing simultaneously the PREV+NEXT buttons. This will insert a 6dB attenuator
between the driver and the amplifier's input (the ATT LED will light), removing the need to reduce the
drive power during tuning. Press PREV+NEXT buttons momentarily again to switch the attenuator out
of the input circuit and to return to the earlier screen. If you use any of PREV or NEXT buttons, the
attenuator will be switched off too, but the information screen will change.
- By pressing repeatedly either the PREV or NEXT button until you reach the TRI scale. This will not
insert the attenuator, so you must be careful to use less than 20W drive (unless the amplifier is near
correct tuning); otherwise the next step will be executed automatically:
- By simply applying a normal (60-85W) drive level while the amplifier is not yet tuned. This will
automatically invoke the TRI tuning aid and will insert the input attenuator (the ATT LED will light) after
one second. The attenuator will be switched off, and the old screen will be returned automatically,
after PTT is released. If near-optimal tuning is achieved, the attenuator will not be inserted again. If
the old screen was unchanged (TRI, selected manually earlier), it will be possible to precisely tune the
N O T E
C A U T I O N
C A U T I O N
Table 4-1. Approximate tuning presets
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