File Size: Kb Number of Views: After downloading, the file may take a moment to open in the browser. Fender – Bassman 5f6a -Schematic Thumbnail. The Bassman 5F6-A preamp contains two voltage amplifiers, one for the bright inputs and one for the Fender Bassman 5F6-A schematic of first two stages. 5F6A Amp Kit Item Code: 5f6a_c_kt We provide a layout and a schematic (on the Technical Details tab), but we do not include step by step assembly.
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If you need more room on the hot side then increase the k resistor to k or k. At about you get the normal 5F6A mid voicing. You simply replace the master volume pot with a resistor on a switch.
List of Mods
When using tube rectification they share the load with the tube rectifier and protect the amp from a rectifier tube short. Run the level at minimum volume when schemmatic using the line out. Be careful, it’s noisy over there. Next the signal moves into the V2A preamp for another gain boost. Preamp tube current is so low it isn’t necessary to actually calculate the value so we can simply estimate it at 3. Rectifier Socket mounted Backup Diodes and 0. The amp’s clean and overdrive tones are a little different in triode mode so this mod opens the amp’s tonal pallet.
The Presence Control cap should have the marking on the ground side. We must also remove the cathode jumper from pins 3 to 8 on the V1 tube socket. DC current load on the power supply is 1.
Since it must be offset to the preamp side of the amp it will actually help balance the weight of the amp. The 27k NFB resistor and 5K schemqtic pot form a voltage divider for the NFB signal so cutting the presence resistance in half also cuts the NFB signal voltage in half which would thicken the clean tone and slow the already lazy transition from clean to dirty tone.
It’s mounted on the preamp side to clear the transformers and actually helps balance the amp’s weight. Disconnect the bottom of the Normal channel k mixing resistor.
Many of the mods on this page apply to the Bassman Reissue. Blue LEDs drop around 3.
Run a jumper wire from the output of the Normal Channel’s k mixing resistor to V1 pin 7. Differences from the original Fender 5F6A layout: You can see how the mid scoop is flattened and what a huge boost in signal you get with the Raw Switch On tone stack ground disconnected even with all three tone pots at max. The upper triode in the schematic above has a dual function.
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But the Cathode Follower does much more than feed xchematic tone stack. Heater current in amps: You could also use two ohm 2 watt resistors in parallel to get the same voltage drop because they are the equivalent of a single 60 ohm 4 watt resistor.
Many people put the bias pot in one of the unused speaker jack holes.
The Cap Board is schemxtic located outside the chassis in a ‘dog house’ next to the choke but it will 5f6q between the power transformer and main circuit board. The first step for this mod is to separate V1’s cathodes so we can use different value bypass capacitors on each channel. So we would install two 0. The “Lead” channel gets a k 1 watt load resistor, 2. This positive signal voltage is also present in the lower cathode because the two cathodes are directly connected.
For more information on screen grid voltage 5c6a overdrive tone see Tube Guitar Amplifier Overdrive. You simply connect both 6.
I did this mod to my 5F6A Bassman and it works great. Tap your center tapped power transformer to create a 50v bias tap.
Note that when we separate the cathode resistors we have to double their value to retain the same bias so V1 pin 8 my unmodified channel needs a 1.
Install ‘ Backup Diodes ‘ on the rectifier tube socket to extend the life of the rectifier tube and protect the amp from a rectifier short failure. This mod will tighten up the overdrive tone and bottom end and make your 5F6A more pedal friendly.
The added resistor also quickens the action of the presence control by changing the pot’s taper from linear to slightly logarithmic. V1’s cathodes are separated using two cathode resistors and two bypass caps.
The voltage drop of an LED is about 1. I was surprised to see the power tubes V4 and V5 are actually hotter than the rectifier tube V6. Guitar Amplifier Preamps2nd Edition.
Notes on the tweed Bassman schematic.
At 50k it will offer a wide range of adjustment and since it’s a multi turn trim pot it is very precise too. The ‘No Feedback’ position makes the amp break up early kind of like a 5E3 Deluxe.
R34 is a standard bias resistor and creates a 1. These modifications reduce midrange scoop for less insertion loss. It adds very little weight to the head cab. I ordered my head cab with about one extra inch in height to fit the taller KT88 tubes. It’s mounted on the preamp side to clear the transformers. Dropping the value of the grid stoppers to 16k or even lower can add some top end sparkle.
The resistor is physically located on the back of the presence pot and is connected from pot input terminal to ground. When evaluating this mod be sure and try a boost pedal to get the gain and distortion up–this is when this mod really shines. You can do this by simply installing a 5Y3 rectifier tube. A KA audio or log pot is wired as a variable resistor in the tone stack ground wire coming out of the Middle tone pot’s terminal 1.