SECTION TWO
GENERAL DESCRIPTION OF CONTROLS
(1) BIAS ADJUST Allows convenient front panel adjustment of the 304TL’s negative grid voltage; normally set at approximately 140mA plate current with no audio signal applied.
(2) FILAMENT Energizes all filaments, HV power supply rectifier filaments, LV power supply and plate supply time delay relay.
(3) READY Indicator lamp illuminates after an approximate one minute time delay for proper warm-up of the HV plate power supply rectifier tubes.
(4) PUSH-BIAS ADJ. Allows checking for proper idle bias current without having to key the transmitter.
(5) PLATE ON Visual indication that high voltage plate supply is energized.
(6) PLATE Energizes high voltage plate supply.
(7) METER Indicates 304TL plate current.
(8) AUDIO GAIN Adjusts audio input level (both MIC and LINE)
(9) CW / PHONE This switch shorts the output of the modulation transformer when placed in the CW position. WARNING: THIS SWITCH SHALL BE PLACED IN THE PHONE POSITION ANYTIME THE MODULATOR IS IN SERVICE. FAILURE TO DO SO COULD SERIOUSLY DAMAGE THE MODULATOR. The switch may be placed in the CW position when the RF amplifier is used as a SSB Linear Amplifier, in which case the modulator is switched off. See SSB OPERATION section for details.
(10) GRID CURRENT Measures RF amplifier 4-1000A grid current. Normal is about 25mA in AM mode.
(11) SCREEN CURRENT Measures RF amplifier 4-1000A screen grid current. Normal is about 100mA in AM mode.
(12) PLATE CURRENT Measures RF amplifier 4-1000A plate current.
(13) PLATE VOLTAGE Measures RF amplifier 4-1000A plate voltage.
(14) LINE VOLTAGE Measures AC line input voltage. Ideal is 240 volts +/- 2.5%
(15) TEMPERATURE Measures 4-1000A ambient air cabinet temperature in degrees Fahrenheit.
(16) GRID BIAS Allows for proper 4-1000A grid bias adjustment for SSB operation. Turn fully CCW for AM Exciter drive.
(17) KEYING When in PTT mode (grid-block keying), the modulator, RF power amplifier, REC MUTE jack (item 50), EXCITER KEY jack (item 51) and antenna T/R relay are remote controlled via KEY PTT jack (item 49), located on rear panel. When in PLATE mode, all items described above are keyed when PLATE ON (item 20) is depressed after a one second time delay.
(18) SCREEN BIAS When in HIGH position (normal), maximum screen voltage is delivered from the screen supply to the 4-1000A screen grid. LOW position reduces the screen voltage and cuts the amplifier’s output power approximately in half. It is suggested to use the LOW position for tune-up.
(19) FILAMENT Enables the 4-1000A filament and negative grid bias supply.
(20) PLATE-ON Enables 4-1000A plate and screen supplies. Also keys devices in item 17, depending on position of KEYING switch.
(21) PLATE-OFF Trips 4-1000A plate and screen supplies and drops KEYING relays.
(22) TUNE Plate tuning vacuum variable capacitor.
(23) LOAD Load tuning vacuum variable capacitor.
(24) INDUCTANCE Inductance (L1a) roller inductor.
(25) 20/40/80/160 Output inductor (L3) band selector switch.
(26) 20/80-160 Output Inductance (L1b) band selector switch.
(27) SSB / AM Screen grid inductance selector switch. Places a 15 Henry choke in series with screen supply circuit when switch is placed in AM mode. WARNING: DO NOT PLACE IN SSB POSITION WHEN 304TL MODULATOR IS IN SERVICE! IMMEDIATE ARCING AND POSSIBLE DAMAGE TO EQUIPMENT MAY RESULT WHEN AUDIO IS IMPRESSED ONTO MODULATION TRANSFORMER. This switch should only be placed in the SSB position when the RF deck is being used as a stand-alone SSB Linear Amplifier or Low Level AM Amplifier. The 304TL modulator should be switched off and CW-PHONE selector switch placed in the CW position.
(28) 160/80/40/20a/20b Input band selector switch.
(29) INPUT TUNING Tune for maximum drive from exciter. (25mA nominal on grid)
(30) MODULATION METER Measures percent modulation, positive and negative or average RF power depending on switch 32 and 33 setting.
(31) CALIBRATE Allows calibration of the modulation meter to full scale when switch 32 is in the RF position.
(32) AF / RF Indicates percent modulation when in the AF position. RF position is for calibration of the modulation meter.
(33) POS / NEG When switch 32 is in the AF position, POS indicates POSITIVE modulation. When in the NEG position, NEGATIVE modulation is indicated on the meter.
(34) MODULATOR Indicates AC power to the 304TL Modulator.
(35) PLATE VOLTAGE Indicates plate voltage is present in the 4-1000A RF deck.
(36) AMPLIFIER Indicates AC power to the 4-1000A RF deck.
(37) PLATE VOLTAGE ADJUST Allows adjustment of the 4-1000A plate voltage.
(38) MOD POWER Main AC circuit breaker for 304TL modulator.
(39) AMP POWER Main AC circuit breaker for 4-1000A RF deck.
(40) MIC Dynamic microphone input, Lo-Z, 600 ohms
(41) SELECT Toggles audio input between MIC and LINE XLR input jacks.
(42) LINE Line level input XLR jack, 600 ohms, balanced.
(43) PTT KEY Modulator PTT jack. Enables 304TL bias grid current when keyed.
(44) DC INPUT Filament, Low Voltage DC, Grid Bias power supply connector plug.
(45) GROUND
(46) FUSE 5A
(47) FUSE 3A
(48) FUSE 15A
(49) PTT KEY External PTT key. Keys transmitter when grounded.
(50) REC MUTE Mutes receive when transmitter is keyed.
(51) EXCITER KEY Keys exciter when transmitter is keyed.
(52) PTT RELAY
TUBE COMPLEMENT
MODULATOR TRANSMITTER
6SJ7-mic preamp 4-1000A-RF Deck
6SN7-phase splitter
6SN7-pre driver
5881/6L6GT-driver (2ea)
304TL-output (2ea)
TRANSMITTER POWER REQUIREMENTS
240 VOLTS AC, 3-WIRE SINGLE PHASE PLUS GROUND, 20 AMPS, 60 HERTZ. LINE VOLTAGE: +/- 2.5%