Kenwood TS-830 Survival Manual

Also see for TS-830: Instruction manual

Contents

136.13 Peak-distortion in the RX audioCause: This is usually caused by one or more problems in the product-detector [PD] on the IFUnit. These problems are: 1. Unmatched PD mixer-diodes, and/or 2. Too-much 455 KHzinjection-voltage at the local-oscillator {LO} port of the PD. 3. No terminating-resistor is usedat the LO-port of the PD. This allow the IF-signal to modulate the LO, which adds distortion.Fixes: Replace the PD diodes, D20, 21, 22, and 23, with 1N6263, Hewlett-Packard HSCH-1001, or similar Schottky-diodes. {D20-24 are on the IF Unit, about 4 cm in front of the left-rearcorner}. Add a approx. 100 Ohm, approx. ¼ W resistor from the junction of R75 and R76 (470Ohms each) to circuit common. If you have an oscilloscope or an RF-voltmeter, the correct LO-voltage, measured across the added 100 Ohm terminating-resistor, should be approx. 600 mVpeak to peak on both USB and LSB. This voltage can be set by alternately adjusting L19 andL20, which are about 3 cm northeast of connector-11.Note: This test point is also available, from the component side of the board, on pin 4 ofconnector-11, to circuit common.6.14 Poor, transmit, SSB carrier-suppression after alignmentCause: Unmatched balanced-modulator diodes.Fix: Replace the original, Germanium diodes, D29 thru D32 with 1N6263, Hewlett-PackardHSCH-1001, or similar Schottky diodes and re-null the carrier with TC3 and VR4 on the IFUnit.Note: HSCH-1001 diodes are hybrid-type Schottky diodes, which have a lower noise-figure ataudio frequencies than ordinary Schottky diodes. Ordinary Schottky diodes will also do the job.6.15 Power-output falls off when the key is held downCause: This is usually the result of electron emission from the screen-grids in the 6146Bs.Screen-emission is caused by operating the filaments of the tubes with excessive filament-voltage for many hours. The excessive filament-voltage overheats the cathode, which causes thecathode's electron-emitting barium coating to slowly evaporate and stick to the screen-grid.When the contaminated screen gets hot during key-down operation, the barium particles on thescreen emit electrons in the wrong direction, toward the cathode, which causes the anode[plate]-current, and power-output, to fall-off.Fix: Replace the 6146B’s with new tubes and insert, for 120 VAC or 240 VAC operation, a0.51 Ohm nominal, 2 W, Metalfilm [MF] resistor in series with the Final Unit PCB-end of theviolet-colored wire, that connects the heater switch to the PCB {that the 6146B sockets aremounted on}. The added voltage-drop in this resistor will decrease the filament-voltage, at thetube-sockets, to approx. 6.1V and will greatly prolong the life of healthy tubes without alteringtheir power-output or IMD.6.16 Premature 12V pilot lamp burnoutFix: Reduce the pilot lamp operating voltage. Put a suitable resistor in series with the wire thatsupplies power to the pilot lamp terminal strip on the bottom of the radio, near the VFO. Startwith approx. 20 Ohms, 0.5W. For optimum life, the pilot lamps should be operated at roughly8-9 V. Reducing the voltage to the meter pilot lamp requires a separate resistor of roughly68 Ohms.Note: inexpensive replacement lamps are available at hobby shops that sell miniature trains.