March 31, 1966 SB-400 Bulletin No: SSB Transmitter SB-400-1D Resistor Overheating Replace R-71 with same value with wattage rating of 1 watt. ----------------------------------------------------------------------------------------------------------------- May 23, 1974 SB-400 Bulletin No: SSB Transmitter SB-400-1 SB-400 & SB-401 Driver Stage Trouble Shooting Guide It is assumed that the basic steps such as making DC voltage measurements, checking tubes and reviewing soldering have been completed. Normal drive to the grid of the 6CL6 is 1.5-2.5V RF on all bands. In some cases it will be higher. 1. Check to see if the blocking bias is being removed from pin 2 of the tube during the key down or tune conditions. The bias is about -15VDC in a key up condition; in the key down condition it is about -.5VDC. 2. Check the cathode resistor to be sure it is of the correct value [SB-401 -- 150 ohms], [SB-400 -- 100 ohms] and correctly installed. 3. Check the wiring of [SB-400 - C90, A, B, C, D], [SB-401 - C4, A, B, C, D], to bandswitch decks BS3R and BS4R. If two of the sections are interchanged, peaking of the coils will be incorrect and very low drive will be present. 4. Incorrect adjustment of the 8MHZ trap can cause suck out on one or more bands. To adjust the trap correctly complete the outlined steps in the manual. 5. Check the screen and plate voltages for the 6CL6 in the key down position. If 50V or better low, check the following components: SB-400; R-93, R-94, RFC-92, C-164, C-97 AND C-99. SB-401; R-4, R-5, RFC-4, C-8, C-7 AND C-58. 6. The capacitors mounted on the driver coils should have as short leads as practical. All leads from the coils to the andswitch should not be any longer than necessary. 7. Bypass capacitors shold have short leads and be placed as close as practical to the chassis. 8. Check the ground of the shield for the shielded cable used in teh plate circuit of the 6CL6. 9. Check the value of [SB-40 R-94] [SB-401 R-5]. The value should be 6.8K and 1W. This resistor determines the drive to the final amplifier stage. This is accomplished due to the RF voltage drop across the resistor. 10. Retighten hardware at the tube sockets, terminal strips and shields. ------------------------------------------------------------------------------------------------------------------ May 23, 1974 SB-400 Bulletin No: SSB Transmitter SB-400-2 SB-400 & SB-401 Hum Trouble Shooting Guide 1. Disconnect one lead of the low voltage filter choke and measure its resistance. Its normal resistance is 120-140 ohms. If the resistance is below 100 ohms the choke is shorted and should be replaced. 2. Check the following capacitors for leakage: SB-400 SB-401 C180 C183 C78 C403 C181 C184 C79 C404 C179 C147 C81 C402 C182A C185 C77A C106 C182B C77B 3. Check terminal strip and terminal board grounds. 4. Retighten hardware at tube suckets, terminal strips, circuit boards and shields. 5. Check the tubes for heater to cathode leakage. 6. Check the grounds for the shield lead of each length of shield cable. 7. Recheck all solder connections. Be sure that the [C79 SB-401], [C181 SB-400] mounting lug is securely soldered to the metallic mounting wafer. ------------------------------------------------------------------------------------------------------------------- May 23, 1974 SB-400 Bulletin No: SSB Transmitter SB-400-3 SB-400 & SB-401 CW Vox Trouble Shooting Guide It is assumed that the basic steps such as making DC voltage measurements, checking the tubes and reviewing the soldering, have been completed. The following information was compiled using SB-400 and SB-401 transmitters in the 80M CW key down condition. The AC signal voltages have been measured with a VTVM throughout the CW Vox circuit and are as follows. Note: The voltages may vary some from transmitter to transmitter. SB-400 SB-401 Pin 11 of V13 .5VAC .5VAC Pin 9 of V13 25VAC 20VAC Pin 9 of V12 1.6VAC 1.2VAC Pin 10 of V12 90VAC 70VAC Pin 11 of V12 1.7VAC 1.5VAC Pin 2 of V12 45VAC 45VAC Pin 7 of V12 18VDC 21VDC By tgracing the AC signal from stage to stage the point of trouble can be isolated and steps taken to correct it. Check for bias removal at pin 9 of V12 when the key is closed. If the bias voltage is not removed check the wiring of FIR LUGS 11 ans 12. Also check for continuity from the key jack to R127 through FIR. A change in VOX delay after operating for a period of time can be caused by leakage in diode [SB-400 D-2] [SB-401 D105]. The other possibility is a change in value of capacitor [SB-400 C123] [SB-401 C141]. Either component could experience a change in operating characteristics due to heat. In such a case mount the two parts on the bottom of the circuit board to correct this condition. -------------------------------------------------------------------------------------------------------------------- July 24, 1978 SB-400 Bulletin No: SSB Transmitter SB-400-4 LMO Drift; Intermittent Frequency Shift Check for a dirty or corroded phono connector on the rear of the LMO. Clean if necessary. -------------------------------------------------------------------------------------------------------------------- August 7, 1978 SB-400 Bulletin No: SSB Transmitter SB-400-5 Loading Capacitor Turns as Plate Capacitor is Rotated This problem can be cause by: - Insufficient friction in the loading capacitor or - Excessive friction between the plate and load tuning shafts. If the problem persists after freeing and lubricating the shafts, install a rubber grommet [PN 73-3] on the loading capacitor shaft between the pulley and the RF cage. Apply slight pressue to the grommet as the pulley setscrew is tighted. This will add enough friction to keep the loading capacitor still while tuning the plate control. Use only as needed. ------------------------------------------------------------------------------------------------------------------- January 21, 1980 SB-400 Bulletin No: SSB Transmitter SB-400-6 Driver Plate Resistor Overheats + + + + Information not yet available + + + + -------------------------------------------------------------------------------------------------------------------- March 7. 1980 SB-400 Bulletin No: SSB Transmitter SB-400-7 Will Not Work with HDP-1220 BW Clipper + + + + Information not yet available + + + + -------------------------------------------------------------------------------------------------------------------- That's all I have for the SB-400 that covers 1966-89. Enjoy! 73 de Joe W7LPF/4 [NNN0KUU] QWCA - SOWP - NCVA - FISTS - RCC Gordonsville, Va 22942 [Orange Co] Wanted: SB-644[A]