(K-MOD0) TROUBLESHOOTING SUPPLEMENT ON BASS TREBLE VOLUME OFF MOD 0 TUBE AMP KIT Use this supplement to help: Measure voltage test points to identify major discrepancies and locate problem areas. (Keep in mind that the voltage measurements will vary slightly from amp to amp. The voltages you measure should be in the same ballpark, but do not expect to get the exact same value.) www.modkitsdiy.com Copyright 0 by modkitsdiy.com
SAFETY Tube amps operate at high voltages that have the potential to injure and kill. Please remember the following when troubleshooting this project. Only work on the amp when you are wide awake and sober. Do not plug the amp in until you have gone through all of the instructions, checking and re-checking each step. Do not turn the amp on until you have connected it to a speaker cabinet or dummy load. Be aware that tubes become very hot when the amp is on and can take up to 0 minutes to cool down after power is turned off. Always follow the one hand rule when working with an amp that is connected to power or may have voltage present. (Any amp that has been plugged in at one time, may have high voltage present). The one hand rule (pictured below): is a safety precaution for working on an amp that is plugged in or could potentially have high voltages present. Using alligator clips with your DMM, clip the ground side to the chassis and use the other side to probe at various test points with one hand. This prevents a fatal shock which can result from current passing through the heart. (Many people even put their other hand in their pocket or behind their back). DANGER HIGH VOLTAGE MAY BE PRESENT ON FILTER CAPACITORS DO NOT TOUCH! Test point sections included in this supplement include: Page FILTER SECTION 3 POWER TUBE ELECTRODES PREAMP TUBE ELECTRODES
Test Point DC Voltage AC Voltage HV B B VDC. VDC. VDC 0. Give the power tube at least 30 seconds to warm up before taking voltage measurements. FILTER SECTION T µf 30V µf 30V µf 30V T 00 0K K HV B B 3
POWER TUBE ELECTRODES Test Point V (pin ) V (pin ) V (pin ) V (pin 3) Name V plate V screen grid V control grid V cathode DC Voltage VDC VDC 0 VDC. VDC K.K 3 W 00 Ω 00µF 00V V PREAMP TUBE ELECTRODES Test Point Name DC Voltage V (pin ) V plate VDC V (pin ) V grid 0 VDC V (pin 3) V cathode 0.0 VDC V (pin ) V plate VDC V (pin ) V grid 0 VDC V (pin ) V cathode 0. VDC V 3 µf 0V
SPEAKER(S) FUSE HOLDER cold wiper hot cold wiper hot cold wiper hot 0KA 0KA MA M BASS TREBLE VOLUME 0 00V INPUT.K.0µF 00V.µF 00V T Treble and Bass controls set to max. Volume control set to a measured resistance of 0kΩ from wiper to ground. µf 30V T3 TP.0 00K T V 3 µf 30V µf 30V µf 0V 00K 0.0 TP3 0.30 TP µf 0V 00K T T 0K 00 K.0 TP.0µF 00V 0K T K.K 3 W 00 Ω 00µF 00V.0 TP Measured at Output Jack connection to the black wire. 0.0 TP V
AC Voltages measured with respect to chassis ground. Treble and Bass controls set to max and Volume set to a resistance of 0kΩ from wiper to ground. Signal: Mexican Strat played with open E strumming. All controls at max and set to Neck pickup (position ). V socket measurements with no tube installed: Pin (plate) = 0 VDC Pin (screen grid) = VDC Pin (control grid) = 0 VDC Pin 3 (cathode) = 0 VDC Pin (filament) =. B 0.0 INPUT M 0.30 TP 00K µ V 3 VDC 0.0 VDC 00K 0p.µ.0µ.0 TP 0KA TREBLE 0KA BASS 0.0 TP3 MA VOL 0kΩ µ 00K VDC V 0. VDC.0µ 0K.0 TP.K K W.03 @ 3 V. VDC max volume 00µ VDC 00 W VDC TP BLU,000 Ω TR Ω.0 TP OUTPUT.K B B TR N00 0.. 0. VDC VDC VDC A FAST BLO /YEL 0 HV 00 W B K W B V = AX / ECC3 V = EL/BQ TR = EX TR = P-T3 0 0 HZ BLACK WHITE GRY N00 0 0K W µ µ µ GREEN POWER WHT 0.03 *. *the filament winding end connected to V pin 3 should measure less than 0.0 with respect to ground. V V EX Resistance Measurments Red() Red(): 0 Ω Red() Red/Yel: Ω Red() Red/Yel: Ω www.modkitsdiy.com Copyright 03 by modkitsdiy.com K-MOD0 Schematic
Open Circuit (No Load) Resistance Measurements EX Primary DCR measurements WHT GRY:.3 Ω WHT : 3. Ω GRY:. Ω V GRY V /YEL Secondary DCR measurements - : Ω /YEL: 3 Ω/3 Ω - : 0. Ω WHT Open Circuit (No Load) Voltage Measurements EX Power Outlet N L L Primary measurements WHT GRY: 0. WHT :. V GRY V /YEL Secondary measurements - : 03 /YEL: 00 0 E GRY:.3 - :. N WHT