1) RELAY (T/R) control cable from transceiver is shorted.
2) Transceiver locked in transmit.
I) Plate current indicated when amplifier is in STBY or receive.
1) 4CX800A/GU74b tube heater-to-cathode leakage or short.
2) Tube bias supply or T/ R bias switch faulty.
P Distorted SSB signal; possible severe television interference.
1) Excessive RF drive from transceiver and/or insufficient amplifier loading.
2) Coaxial connector, coax feedline, antenna feedpoint balun, tuner, or antenna trap
arcing on voice peaks.
3) RF feedback from antenna into transceiver via the transceiver power cord, micro
phone or key cable, or other unshielded station patch cables.
4) Poor station RF ground.
K) Low frequency audio hum on transmitted signal.
1) Defective microphone cord (especially, broken ground lead).
2) Dynamic (magnetic) microphone located within about two feet of
91/3
power
transformer. All dynamic microphones pick up some magnetically-coupled hum from
the external field of nearby power transformers. In cases where objectionable hum is
experienced while using the
91/3
and popular microphones such as the Heil series,
the problem usually can be resolved by keeping the microphone at least 18 to 24
inches from the front of the amplifier and insuring that transceiver mike gain (speech
processing) and internal drive (ALC) levels are not adjusted to exceed 10 dB. In rare
cases it may be necessary to use a ceramic or condensa- type microphone.
16
Summary of Contents for ETO 91B
Page 4: ...C21 C24 C20 C26 under Power Supply Board PS J1 J2...
Page 5: ...L4 BL1 HV Crowbar Vacuum Relay Power K2 Relays P1 XFMR T i S3 Interlock Figure 1 9ip Top View...
Page 10: ...FIGURE 5 91B REAR PANEL...
Page 22: ...91fi SCHEMATICS 19...
Page 25: ......
Page 26: ...B R E A K D 23 T G U N LO C K 10 M E TE R S FIGURE 7 91 CONTROL BOARD...
Page 28: ...FIGURE 8 91 S DISPLAY BOARD...
Page 29: ...er FIGURE 9 91 POWER SUPPLY BOARD...
Page 30: ...R13 J1 FIGURE 10 91 3 HV FILTER SCREEN SUPPLY...
Page 31: ...FIGURE 11 91 INPUT BOARD...
Page 32: ...FIGURE 12 91 OUTPUT RF WATTMETER FIGURE 13 91 MULTIMETER SWITCH...
