Mod K-700 Instructions Manual

Bass to tremolo conversion kit

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BASS TO TREMOLO CONVERSION KIT (K-700)

220k

50k-

INTENSITY

.01

100k

Use these instructions and your vintage Fender guitar amplifier to learn:

How to convert the "Bass Instrument" channel of a Bassman amp into a tremolo

effect for the "Normal Channel".

www.modkitsdiy.com

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Summary of Contents for Mod K-700

Page 1 BASS TO TREMOLO CONVERSION KIT (K-700) 220k 50k- INTENSITY 100k Use these instructions and your vintage Fender guitar amplifier to learn: How to convert the “Bass Instrument” channel of a Bassman amp into a tremolo effect for the “Normal Channel”.
Page 2: Table Of Contents
Table of Contents Safety ……………………………………………………3 Parts List ……………………………………………4, 5 Tools …………………………………………....6 Soldering Tips ……………………………………7, 8 Preliminaries ……………………………………………9 Test Points …………………………………………...10 Bass to Tremolo Modification …………………...11 – 24 Style A …………………………………………...12 – 17 Style B ……………………………………………18 – 23 Schematics …………………………………………...12, 18 Terminal Strip Mounting Tips …………………...24...
Page 3: Safety
HIGH VOLTAGE MAY BE PRESENT DANGER BE CAREFUL! STANDBY UNPLUG Safety “Caution: to prevent electrical shock, do not remove chassis or metal cover attached to chassis. No user serviceable parts inside. Refer servicing to qualified personnel only.” -the back of an amp We have quoted the back of an amp to stress the importance of putting safety first when working on this type of equipment.
Page 4: Parts List
Parts List Part Number Quantity Description C-MD1-630 0.1 F capacitor .1 F 630V C-MD01-630 0.01 F capacitor .01 F 630V C-MD022-630 0.022 F capacitor .022 F 630V C-ET22-50 22 F polarized capacitor 22 F 50V R-A100K 100k , ½W resistor 100K brown black...
Page 5 Parts List (continued) Part Number Quantity Description R-B1D5K 1.5k , 1W resistor 1.5K (This value is used in amps with shared preamp tube cathodes only – Like Bassman 100) brown green gold R-VOP1020 Optocoupler R-VC50K-RA 50k potentiometer (reverse audio taper) R-VC3M-RA 3M potentiometer (reverse audio taper) W-SC-11...
Page 6: Tools
Tools 1. Digital Multi-Meter (DMM) – a meter for measuring voltage, current, resistance, and sometimes capacitance. 2. Alligator Clip Test Leads – connect to your DMM for hands free measurements. These are useful when setting the power tube bias and for safety when taking electrical measurements.
Page 7: Soldering Tips
Soldering Tips (circuit boards) Work in a ventilated area with a fan to blow the smoke from your face. Allow the soldering iron to heat up to the point where the solder melts quickly when touched to the iron's tip. Clean the soldering iron's tip by wiping it across a wet sponge before applying solder to it.
Page 8 Soldering Tips (solder lugs) Bend the component lead or wire ending and wrap it around the connection point. Make sure it is not too close to a neighboring component which could cause an unintended connection. Wrap the component lead so that it can hold itself to the connection point. Touch the soldering iron to both the component lead and the connection point allowing both to warm up just before applying the solder to them.
Page 9: Preliminaries
Preliminaries Please make sure you do the following before opening your amp: Unplug the power cord. Turn the power switch off. Turn the standby switch off (down position). Give the power tubes 10 minutes to cool down. STANDBY COOL UNPLUG Make sure the power tubes have cooled down enough to touch.
Page 10: Test Points
NORMAL BRIGHT Jewel MASTER Lamp TREB BASS VOLUME Holder Inside View of Amp Chassis - not all components are shown POWER STANDBY TP(3) TP(4) TP(1) TP(5) TP(2) Test Points If there is a high voltage present at any of these test points, there may be something wrong with your amp.
Page 11: Bass To Tremolo Modification
Bass to Tremolo Modification Step 1: Determine which style of Bassman you have. (STYLE-A) Circuit Board To Phase Inverter To “Normal” Input To “Bass” Input 7025/12AX7 POWER TUBE 12AT7 7025/12AX7 STYLE A (follow pages 12 – 17) We define this style of amp as having the following characteristics: a) The amp has 3 preamp tubes including two 7025/12AX7 tubes and one 12AT7 tube.
Page 12: Schematics
Bass to Tremolo Modification Schematic (STYLE-A) Here is a schematic representation of this mod for style A amps. It is not necessary to be able to read the schematic in order to complete the mod. 375 VDC 100K 100K BRIGHT...
Page 13 DEEP BASS BASS TREB Step 2: Disconnect the “Bass” channel front panel controls and wires. Depending upon which amp model you have, the layout of components may vary slightly. The main idea of this step is to remove the bass channel controls so that we can mount the tremolo controls.
Page 14 TREB DEEP BASS BASS Step 3: Remove the bass channel controls from the front panel. 1) Deep switch 2) Volume pot 3) Treble pot 4) Bass pot Step 3 (MID version): If your bass channel has a mid control, leave the last of the four pots mounted, but completely disconnect it from the circuit.
Page 15 .022 F 630V BASS FOOTSWITCH Step 6: Remove unnecessary circuit board SPEED components. INTENSITY Each instruction line number here corresponds to the numbers on the drawing where missing components are outlined. 375V Power Supply Line 1) Remove the cathode bias components connected to V1 pin 3.
Page 16 Step 8: Mount the three terminal strips. .022 F 630V BASS FOOTSWITCH See Terminal Strip Mounting SPEED INTENSITY Section (p. 24) Fasten the three terminal strips to existing screws in the chassis as shown and in similar locations. 1) Mount T1 on a screw near the footswitch jack. 2) Mount T2 using the fiber board screw.
Page 17 .022 F 630V BASS FOOTSWITCH bias diode – not shown in actual location SPEED INTENSITY 10 F 100V Cathode Anode power tube socket – not drawn to scale or in actual location 100K 22 F 50V .1 F 630V 1.5K Step 10: Wire it up.
Page 18 Bass to Tremolo Modification Schematic (STYLE-B) Here is a schematic representation of this mod for style B amps. It is not necessary to be able to read the schematic in order to complete the mod. 400 VDC 500p 100K 100K...
Page 19 DEEP BASS BASS TREB Step 2: Disconnect the “Bass” channel front panel controls and wires. Depending upon which amp model you have, the layout of components may vary slightly. The main idea of this step is to remove the bass channel controls so that we can mount the tremolo controls.
Page 20: Style B
BASS TREB DEEP BASS Step 3: Remove the bass channel (STYLE-B) controls from the front panel. 1) Deep switch 2) Volume pot 3) Treble pot 4) Bass pot Step 3 (MID version): If your bass channel has a mid control, leave the last of the four pots mounted, but completely disconnect it from the circuit.
Page 21 .022 F 630V BASS FOOTSWITCH Step 6: Remove unnecessary circuit board SPEED components. INTENSITY Each instruction line number here corresponds to the numbers on the drawing where missing components are outlined. 400V Power Supply Line 1) Remove the cathode bias components connected to V1 pin 3.
Page 22 .022 F 630V BASS FOOTSWITCH Step 8: Mount the three terminal strips. SPEED INTENSITY See Terminal Strip Mounting Section (p. 24) Fasten the three terminal strips to existing screws in the chassis as shown and in similar locations. 1) Mount T1 on a screw near the footswitch jack. 100K 2) Mount T2 using the fiber board screw.
Page 23 .022 F 630V BASS FOOTSWITCH bias diode – not shown in actual location SPEED INTENSITY Anode Cathode 100K power tube socket – not drawn to scale or in actual location .1 F 630V 1.5K “sleeve” Step 10: Wire it up. “tip”...
Page 24: Terminal Strip Mounting Tips
(STRIP MOUNTING) Terminal Strip Mounting Tips We will be adding extra circuit components by mounting them on three terminal strips. The cap cover and circuit boards are held in to place by several self-tapping screws which give us a way to mount the terminal strips without drilling new holes in the chassis.