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Adding Bias Tremolo to the 5F6A Bassman
Adding Bias Tremolo to the 5F6A Bassman
Why is there no tremolo for the Vintage Bassman?
Why is there no tremolo for the Vintage Bassman?
The 5F6A Bassman is a classic amp and much has been enhanced and modified in this amp and it's clones. Rob Robinette has compiled a great summary of many mods and other useful info about the Bassman. However, none of the mods add a good tremolo to the chassis.
The 5F6A Bassman is a classic amp and much has been enhanced and modified in this amp and it's clones. Rob Robinette has compiled a great summary of many mods and other useful info about the Bassman. However, none of the mods add a good tremolo to the chassis.
Substantial barriers have to be overcome to add tremolo. First, the chassis is rather cramped and there is little room (and significant work) to add another tube and additional circuits. Secondly, although bias tremolo sounds great and is a huge success in the Tremolux, Princeton and similar smaller amps, a bias tremolo for a 40-50w 6L6 output stage is not a simple matter. Because of that, few 6L6 or EL34 high-power amps use bias tremolo. Most employ a LDR (light dependent resistor) instead, which produces a different tremolo tone. This article explains the various tremolo approaches. A chapter in this book also explains bias tremolo operation and why it sounds so good.
Substantial barriers have to be overcome to add tremolo. First, the chassis is rather cramped and there is little room (and significant work) to add another tube and additional circuits. Secondly, although bias tremolo sounds great and is a huge success in the Tremolux, Princeton and similar smaller amps, a bias tremolo for a 40-50w 6L6 output stage is not a simple matter. Because of that, few 6L6 or EL34 high-power amps use bias tremolo. Most employ a LDR (light dependent resistor) instead, which produces a different tremolo tone. This article explains the various tremolo approaches. A chapter in this book also explains bias tremolo operation and why it sounds so good.
With all the impediments, pedals have been the only practical tremolo option for Bassman. But pedal effects have limitations since they are so early in the signal chain, and it's relatively difficult and expensive to implement a true tube bias tremolo in a pedal. One example is the Kingsley Bard, which sounds great, but almost all other tremolo pedals use an LDR or similar technology. In an ideal world, the classic Bassman deserves a classic tube bias tremolo. That's just the way it should be.
With all the impediments, pedals have been the only practical tremolo option for Bassman. But pedal effects have limitations since they are so early in the signal chain, and it's relatively difficult and expensive to implement a true tube bias tremolo in a pedal. One example is the Kingsley Bard, which sounds great, but almost all other tremolo pedals use an LDR or similar technology. In an ideal world, the classic Bassman deserves a classic tube bias tremolo. That's just the way it should be.
What is the Amp-Aid tremolo module?
What is the Amp-Aid tremolo module?
Amp-Aid is proud to offer the BMTrem2 module. This is a new bias tremolo system that is designed and optimized for the 5F6A chassis. The module fits within the 5F6A chassis, replacing the un-needed ground switch with a concentric control so tremolo speed and depth are both accessible from the front panel. No chassis rewiring is needed, in fact only 3 wires connect the module to the existing Bassman circuits.
Amp-Aid is proud to offer the BMTrem2 module. This is a new bias tremolo system that is designed and optimized for the 5F6A chassis. The module fits within the 5F6A chassis, replacing the un-needed ground switch with a concentric control so tremolo speed and depth are both accessible from the front panel. No chassis rewiring is needed, in fact only 3 wires connect the module to the existing Bassman circuits.
Only high quality components are used, including a sealed concentric potentiometer for scratch-free control of tremolo speed and depth. Installation is literally done in a few minutes.
Only high quality components are used, including a sealed concentric potentiometer for scratch-free control of tremolo speed and depth. Installation is literally done in a few minutes.
You won't find anything like the BMTrem2 system in use today. The BMTrem2 is a completely new approach to bias tremolo. The BMTrem2 module overcomes the barriers mentioned above, and more importantly, it sounds thick and rich, a perfect complement to the Bassman character. The bias tremolo sound is unique in its harmonic richness - it's not just a volume modulation. It adds a harmonic character to the amp tone that varies with the tremolo rate and depth.
You won't find anything like the BMTrem2 system in use today. The BMTrem2 is a completely new approach to bias tremolo. The BMTrem2 module overcomes the barriers mentioned above, and more importantly, it sounds thick and rich, a perfect complement to the Bassman character. The bias tremolo sound is unique in its harmonic richness - it's not just a volume modulation. It adds a harmonic character to the amp tone that varies with the tremolo rate and depth.
If you're looking for a single addition to make your Bassman unique and more versatile, this is it. The price is right, it's the perfect use for that useless ground switch panel position, and the sound is great - its literally unlike anything a Bassman has produced before and it creates a whole new tonal dimension to explore.
If you're looking for a single addition to make your Bassman unique and more versatile, this is it. The price is right, it's the perfect use for that useless ground switch panel position, and the sound is great - its literally unlike anything a Bassman has produced before and it creates a whole new tonal dimension to explore.
Here is a just a sample of what it sounds like.
Here is a just a sample of what it sounds like.
How do I get it?
How do I get it?
The BMTrem2 module is available assembled or a kit. If you're not comfortable building circuits, consider asking a qualified amp technician to do it for you. Amp-Aid is pleased to announce it has a distribution agreement with Kendrick Amplifiers. Contact Gerald Weber at 512 932 3130 or gerald20@earthlink.net. Kendrick is taking orders and shipping now.
The BMTrem2 module is available assembled or a kit. If you're not comfortable building circuits, consider asking a qualified amp technician to do it for you. Amp-Aid is pleased to announce it has a distribution agreement with Kendrick Amplifiers. Contact Gerald Weber at 512 932 3130 or gerald20@earthlink.net. Kendrick is taking orders and shipping now.
How do I build and install the tremolo module?
How do I build and install the tremolo module?
Instructions for assembly and installation are below. Module assembly takes about 30-45 mins and installation into a Bassman chassis is 15-30 mins.
Instructions for assembly and installation are below. Module assembly takes about 30-45 mins and installation into a Bassman chassis is 15-30 mins.
How do amp techs offer the BMTrem2 installation to clients?
How do amp techs offer the BMTrem2 installation to clients?
Amp-Aid supports amp technicians who offer BMTrem2 installations to their clients. Amp techs are in the best position to deliver a quality build and installation.
Amp-Aid supports amp technicians who offer BMTrem2 installations to their clients. Amp techs are in the best position to deliver a quality build and installation.
Contact Gerald Weber at 512 932 3130 or gerald20@earthlink.net
Contact Gerald Weber at 512 932 3130 or gerald20@earthlink.net
Can the BMTrem2 module be added to other amps?
Can the BMTrem2 module be added to other amps?
The BMTrem2 kit is designed for the 5F6A and its clones. However, other amps can use this kit with minor component value changes. The BMTrem2 module can be adapted to work with almost any tube amp using a long-tail phase inverter. Of course you'll need to verify physical chassis and panel space too.
The BMTrem2 kit is designed for the 5F6A and its clones. However, other amps can use this kit with minor component value changes. The BMTrem2 module can be adapted to work with almost any tube amp using a long-tail phase inverter. Of course you'll need to verify physical chassis and panel space too.
Contact Gerald Weber at 512 932 3130 or gerald20@earthlink.net for more information.
Contact Gerald Weber at 512 932 3130 or gerald20@earthlink.net for more information.
BMTrem2 build and installation instructions
BMTrem2 build and installation instructions
The Amp-Aid BMTrem2 kit contains the following:
The Amp-Aid BMTrem2 kit contains the following:
PCB1 the module PC board
PCB1 the module PC board
C1 .68uf capacitor
C1 .68uf capacitor
C2 .68uf capacitor
C2 .68uf capacitor
C3 .68uf capacitor
C3 .68uf capacitor
C4 47uf/16v capacitor
C4 47uf/16v capacitor
D1 1N5252B 24v 1/2w zener diode
D1 1N5252B 24v 1/2w zener diode
P1 Burns sealed dual concentric pot w/switch
P1 Burns sealed dual concentric pot w/switch
Q1 2N3904
Q1 2N3904
Q2 2N3904
Q2 2N3904
Q3 KSP44
Q3 KSP44
Q4 2N3906
Q4 2N3906
Q5 ZTX560
Q5 ZTX560
Q6 ZTX560
Q6 ZTX560
R1 510
R1 510
R2 100k
R2 100k
R3 150k 2w
R3 150k 2w
R4 180k
R4 180k
R5 560k
R5 560k
R6 27k
R6 27k
R7 56k
R7 56k
R8 5.1k
R8 5.1k
R9 51k
R9 51k
R10 100k
R10 100k
R11 22k
R11 22k
R12 39k
R12 39k
R13 22k
R13 22k
R14 150k
R14 150k
R15 150k 1w
R15 150k 1w
R16 150k 1w
R16 150k 1w
Metal (black) dual concentric knobs
Metal (black) dual concentric knobs
Module Assembly
Module Assembly
Assembly is straight forward by following the component layout shown below. This diagram shows the top-side PCB traces and the component outlines.
Assembly is straight forward by following the component layout shown below. This diagram shows the top-side PCB traces and the component outlines.
Start by identifying each component to make sure there is no confusion about them. Note that there are four 150K resistors. They differ in that R15 and R16 are metal film 1w resistors, R3 is a 2w metal film resistor and R14 is a carbon film resistor. Make sure you distinguish these correctly.
Start by identifying each component to make sure there is no confusion about them. Note that there are four 150K resistors. They differ in that R15 and R16 are metal film 1w resistors, R3 is a 2w metal film resistor and R14 is a carbon film resistor. Make sure you distinguish these correctly.
R1-R16 and C1-C3 can be installed in any orientation. However, C4, D1, and Q1-Q6 must be installed with the indicated polarity/orientation. Stop right here and seek professional assistance if you're not perfectly clear on how to proceed.
R1-R16 and C1-C3 can be installed in any orientation. However, C4, D1, and Q1-Q6 must be installed with the indicated polarity/orientation. Stop right here and seek professional assistance if you're not perfectly clear on how to proceed.
When all the components are installed and soldered, check the board for orientation or placement errors and check the solder joints for suspect (cold) joints and errant solder bridges. High voltages are applied to the board during operation, so take your time and get it right. This is a case where it takes 10x as long to fix a problem than it takes to avoid one in the first place.
When all the components are installed and soldered, check the board for orientation or placement errors and check the solder joints for suspect (cold) joints and errant solder bridges. High voltages are applied to the board during operation, so take your time and get it right. This is a case where it takes 10x as long to fix a problem than it takes to avoid one in the first place.
This image shows a bare board and a partially assembled board with all the resistor and capacitors installed. Note the orientation of C4. Leave a small (1mm) gap under R3 as this resistor gets warm during operation and a gap improves airflow and prevents PCB damage.
This image shows a bare board and a partially assembled board with all the resistor and capacitors installed. Note the orientation of C4. Leave a small (1mm) gap under R3 as this resistor gets warm during operation and a gap improves airflow and prevents PCB damage.
This image shows all the resistors, capacitors, and semiconductors installed. Note that all the transistor flat surfaces face the same direction.
This image shows all the resistors, capacitors, and semiconductors installed. Note that all the transistor flat surfaces face the same direction.
Finally, this last image shows all the components installed. The module is ready for chassis installation.
Finally, this last image shows all the components installed. The module is ready for chassis installation.
Chassis Installation
Chassis Installation
Once the PCB is assembled, chassis installation can begin. The exact chassis appearance may vary, but most 5F6A chassis are similar. Again, make sure you are completely comfortable with the outlined sequence of steps before you begin.
Once the PCB is assembled, chassis installation can begin. The exact chassis appearance may vary, but most 5F6A chassis are similar. Again, make sure you are completely comfortable with the outlined sequence of steps before you begin.
Get a tech to help or do the install for you if you have any doubts or questions about any of this. It's not worth electrocution - whatever it is - it's not worth it.
Get a tech to help or do the install for you if you have any doubts or questions about any of this. It's not worth electrocution - whatever it is - it's not worth it.
1 - There are high voltage hazards in the amp so make sure you unplug it and discharge all capacitors before proceeding. Get professional tech help unless you know what you're doing and you understand the risks involved.
1 - There are high voltage hazards in the amp so make sure you unplug it and discharge all capacitors before proceeding. Get professional tech help unless you know what you're doing and you understand the risks involved.
2 - Remove the back cover to reveal the chassis internals.
2 - Remove the back cover to reveal the chassis internals.
3 - If your amp has a 3 prong power cord, remove the ground switch. It's probably already disconnected and just filling the hole. If your amp has an old 2 prong cord. Stop here and get a tech to replace it with a 3 prong cord and disconnect the ground switch. A tech knows how to do this safely. Even if you don't do anything else to the amp, have a tech replace that 2 prong cord with a 3 prong cord.
3 - If your amp has a 3 prong power cord, remove the ground switch. It's probably already disconnected and just filling the hole. If your amp has an old 2 prong cord. Stop here and get a tech to replace it with a 3 prong cord and disconnect the ground switch. A tech knows how to do this safely. Even if you don't do anything else to the amp, have a tech replace that 2 prong cord with a 3 prong cord.
4 - Once you have a 3 prong cord properly installed, and the now useless ground-switch removed, clear the area below the ground switch panel hole. You may have wires running through that area and you'll need to reposition them to make room for the module. Below is a photo of an installed module. You'll need to make room for it. A 5F6A chassis should not have anything in that area except for some wires that can easily be moved aside.
4 - Once you have a 3 prong cord properly installed, and the now useless ground-switch removed, clear the area below the ground switch panel hole. You may have wires running through that area and you'll need to reposition them to make room for the module. Below is a photo of an installed module. You'll need to make room for it. A 5F6A chassis should not have anything in that area except for some wires that can easily be moved aside.
Here is a picture of a Weber clone 5F6A before installing the module. Notice the ground switch to the left of the fuse and a bundle of unused transformer wires below that.
Here is a picture of a Weber clone 5F6A before installing the module. Notice the ground switch to the left of the fuse and a bundle of unused transformer wires below that.
The next picture shows the module in final position with knobs attached. The tremolo controls stick up through the panel, and below the control the BMTrem2 PC board is visible. (Ignore the white box to the left of the PC board, it has nothing to do with the tremolo system). Make sure the PCB itself is clear of all contact with the chassis or tube sockets. No part of the PCB should touch the Bassman metal surfaces or connections.
The next picture shows the module in final position with knobs attached. The tremolo controls stick up through the panel, and below the control the BMTrem2 PC board is visible. (Ignore the white box to the left of the PC board, it has nothing to do with the tremolo system). Make sure the PCB itself is clear of all contact with the chassis or tube sockets. No part of the PCB should touch the Bassman metal surfaces or connections.
5 - Now that you verified that the module will fit properly, remove the module and prepare the wire harness that connects it to the Bassman circuits.
5 - Now that you verified that the module will fit properly, remove the module and prepare the wire harness that connects it to the Bassman circuits.
There are 3 wires that run from the pads labeled on the PC board. B+ and Gnd are connections to the Bassman power supply at the points marked in the figures below. The Mod wire connection is made to either pin 3 of the phase inverter socket, or the point marked on the board in the figure below (whichever is more convenient). Use good quality 26 or 24 gauge hookup wire (not supplied). A 3 conductor shielded cable can also be used, although shielding isn't really necessary.
There are 3 wires that run from the pads labeled on the PC board. B+ and Gnd are connections to the Bassman power supply at the points marked in the figures below. The Mod wire connection is made to either pin 3 of the phase inverter socket, or the point marked on the board in the figure below (whichever is more convenient). Use good quality 26 or 24 gauge hookup wire (not supplied). A 3 conductor shielded cable can also be used, although shielding isn't really necessary.
Avoid excess wire length, although a bit of slack makes installation of the module easier. The wires can be twisted together or not, whatever makes the installation easier. The figures below show the connections of the wires to the Bassman circuit.
Avoid excess wire length, although a bit of slack makes installation of the module easier. The wires can be twisted together or not, whatever makes the installation easier. The figures below show the connections of the wires to the Bassman circuit.
The first image is derived from a Mojotone layout drawing, the second is from a Weber clone layout figure. Both show exactly the same 3 connections so there should be no confusion about where the 3 wires connect.
The first image is derived from a Mojotone layout drawing, the second is from a Weber clone layout figure. Both show exactly the same 3 connections so there should be no confusion about where the 3 wires connect.
Lastly, as a sanity check, here is a schematic with the same points marked. Solder the three wires to both the PCB pads and the amp circuits. Nothing is removed and nothing is cut. You only add these three wires and connections to the existing circuit.
Lastly, as a sanity check, here is a schematic with the same points marked. Solder the three wires to both the PCB pads and the amp circuits. Nothing is removed and nothing is cut. You only add these three wires and connections to the existing circuit.
The next image shows the module with wire harness attached, ready for final mounting.
The next image shows the module with wire harness attached, ready for final mounting.
6 - Now that the wire harness is soldered to the module, it can be mounted permanently. Fit it into the ground switch hole and fasten the nut on the control bushing. A washer is used since the switch hole is slightly oversized for the control.
6 - Now that the wire harness is soldered to the module, it can be mounted permanently. Fit it into the ground switch hole and fasten the nut on the control bushing. A washer is used since the switch hole is slightly oversized for the control.
Tighten the nut carefully to avoid stripping. Inspect all the wires and connections again to make sure nothing is broken or misplaced and there is no contact between the module and surrounding metal.
Tighten the nut carefully to avoid stripping. Inspect all the wires and connections again to make sure nothing is broken or misplaced and there is no contact between the module and surrounding metal.
This image shows the module in final position, ready for attaching the knobs.
This image shows the module in final position, ready for attaching the knobs.
7 - Attach the knobs to the BMTrem2 controls. Replace the back cover of the amp. Before turning it on, turn the depth control (upper control) CCW until a switch click is felt. With the depth control at minimum, a switch completely disconnects the module from the Bassman circuit signals. The tremolo is completely disconnection in that position so it's impossible for the module to impact the amp's original behavior.
7 - Attach the knobs to the BMTrem2 controls. Replace the back cover of the amp. Before turning it on, turn the depth control (upper control) CCW until a switch click is felt. With the depth control at minimum, a switch completely disconnects the module from the Bassman circuit signals. The tremolo is completely disconnection in that position so it's impossible for the module to impact the amp's original behavior.
8 - Turn on the amp (with the depth control still fully CCW). Verify that it works and sounds as it always has. The BMTrem2 module has no impact on the amp tone or behavior with the depth control set to min.
8 - Turn on the amp (with the depth control still fully CCW). Verify that it works and sounds as it always has. The BMTrem2 module has no impact on the amp tone or behavior with the depth control set to min.
When ready, turn the depth control CW and after about 1/4 turn, you should begin to hear the tremolo effect. The tremolo speed is changed with the bottom knob. Note that the speed reduces as the knob is turned CW. This may take some getting used to, but it is a small artifact that arises due to the limited space (and options) for controls. Think of it as a "feature".
When ready, turn the depth control CW and after about 1/4 turn, you should begin to hear the tremolo effect. The tremolo speed is changed with the bottom knob. Note that the speed reduces as the knob is turned CW. This may take some getting used to, but it is a small artifact that arises due to the limited space (and options) for controls. Think of it as a "feature".
That's it - you can now explore and enjoy the new bias tremolo tones coming from your Bassman. We hope you're as pleased with the outcome as we are proud to make it possible.
That's it - you can now explore and enjoy the new bias tremolo tones coming from your Bassman. We hope you're as pleased with the outcome as we are proud to make it possible.
We're happy to hear from techs and/or players. Send your questions, comments, and reactions to ampaid16@gmail.com or Gerald gerald20@earthlink.net
We're happy to hear from techs and/or players. Send your questions, comments, and reactions to ampaid16@gmail.com or Gerald gerald20@earthlink.net
Lastly, you may wonder, what's the Ped connection on the PCB for? As you probably suspect, it's for a pedal to turn tremolo on/off. If a jack is available in the chassis, run a wire from the Ped pad to the jack pin. When Ped is left floating, tremolo is active. Grounding Ped to any convenient ground point (including chassis) will disable the tremolo.
Lastly, you may wonder, what's the Ped connection on the PCB for? As you probably suspect, it's for a pedal to turn tremolo on/off. If a jack is available in the chassis, run a wire from the Ped pad to the jack pin. When Ped is left floating, tremolo is active. Grounding Ped to any convenient ground point (including chassis) will disable the tremolo.
DISCLAIMER: Amp-Aid is not liable for any damages or injuries in connection with this kit or with any amplifier. The customer must determine suitability of this product, and be responsible for its construction, installation, and use.
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