DAMAGE RESULTING FROM USE OF A FUSE OF INCORRECT SIZE OR TYPE WILL
NOT BE COVERED UNDER WARRANTY AND MAY VOID THE WARRANTY.
PLATE OVERCURRENT RELAY — This relay will quickly turn off the amplifier in the
event of grossly excessive plate current or fault in the high voltage circuitry. The relay will
not prevent tube or other damage due to either short or long term overdrive or improper
tuning. It is the operator's responsibility to ensure safe tuning, drive, and general operating
conditions. Should the overcurrent relay trip and remove AC power from the amplifier, determine and
correct the cause of the trip before turning the 91/3 on again.
IDLING PLATE CURRENT AND ELECTRONIC BIAS CONTROL (EBS)
Idling plate current of the ETO 91/3 is approximately 350 to 400 mA during transmission. A
detector senses RF drive, and reduces plate current to 30-50 mA during pauses in speech and
key-up intervals, thus substantially reducing average power supply loading, heat generation,
and wasted energy.
ARC & MISTUNING PROTECTION
FID'S exclusive circuit senses the beginning of any RF arc in, for example, a TUNE or LOAD
variable capacitor and automatically switches the 91/3 to standby within a few milliseconds.
This system has virtually eliminated RF arc damage in current ETO amplifiers. The system
similarly detects severe mis-tuning of the 91/3, and if drive exceeds about 15 watts switches
the amplifier to standby. The 15 watt threshold permits safe tuneup at low power levels
using the TUNE indicator, without aggravating and unnecessary trip-outs.
PREVENTIVE MAINTENANCE - The amplifier interior, particularly high voltage areas,
should be cleaned with a vacuum cleaner and a soft bristle brush frequently enough to
prevent visible accumulation of dust. In extremely dusty conditions it may be advisable to
secure a thin air filter of the type used for window air conditioners across the air intake on the
rear panel. The ETO accessory cooling fan also should be installed to insure adequate cooling
airflow.
There are no user-accessible lubrication points in the amplifier. Do not apply oil or grease to
any of the components. The exterior of the ETO 91/3 may be cleaned with a mild household
liquid detergent such as Formula 409 or Fantastik. Do not use chemical solvents, as these may
severely damage the front panel or cabinet finish. Never use an abrasive cleaner.
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