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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For an interior access only bias pot I highly recommend this Bourns 50k multi-turn trim pot part YLF. The power tubes amplify the mirror image signals and while one tube plate is “pushing” the signal through the output transformer primary winding coilthe other power tube is “pulling” it.

Build a 3 tube Bassman Micro 2 watt practice amp: My Tung-Sol power tubes biased at AC from the power transformer: Click here for a hi 5ff6a pdf. LTSpice model of the standard 5F6A bias circuit. Guitar Amplifier Preamps2nd Edition. You can use this circuit that’s loosely based on the Marshall JCM to create an adjustable bias tap without using a power transformer with a dedicated 50v bias tap.

Grid stoppers zchematic help prevent blocking distortion and protect your power tubes from damage when driven hard into overdrive when grid current begins to flow.

Ground switch is deleted3-Prong power cord, balanced 6. I like to 5fa the resistors on one of the power tube’s socket as shown below. Tighten up and modernize sschematic channel’s clean and overdrive tone. It is much more difficult to add to an existing amp so for modding an existing amp I recommend the Type-3 master volume. Add power amp stability and decrease blocking distortion.

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EngineeringMusic. The calculator shows a DC plate-to-cathode voltage of V. When each wire carries an 5f6q AC voltage 60Hz hum will be cancelled out by twisting the heater wires together. A dual gang KA pot one shaft turns both pots, audio or log taper replaces the two k power tube grid leak resistors. This modification separates the V1 cathodes, increases the “Lead” channel’s load resistor, cathode resistor, reduces its bypass capacitor and reduces the coupling capacitor.


The jumper does not affect 6L6 or 6V6 or any schemafic tubes. You can install a 2-way toggle switch on the 5F6A to flip between normal fixed and cathode bias.

A pair of KT88 ‘s biased at If we were worried about running a valve rectifier too close to its maximum Va rms [AC voltage rating], we could place one or more silicon diodes having a much higher peak inverse voltage in series with each anode, as protection elements.

A GZ34 will drop 10 to 15 volts more than solid state and the 5Y3 will drop around 60v more than solid state. V1’s extra caps and resistors can get a little crowded on the circuit board so it’s a good idea to raise the hot cathode resistors higher off the circuit board than the coupling caps to 5c6a cooling and minimize heat transfer from the resistors to the caps. You can also fatten up the clean and overdrive tone by intentionally mismatching the two tubes’ bias which increases harmonic distortion.

Prowess Amplifiers – Fender – Schematics – Bassman 5f6a – Schematic

These resistors are not required if your power transformer has a 6. For more info on channel jumpering schemaric this. It’s also a good idea to turn schematjc bias down some before installing a new set of tubes and then bias them immediately upon power up. A 22M to 44M resistor and. Preamp tube V1B gives the Bright channel guitar signal its first gain boost. There’s a 6″ Eminence H hemp coned practice speaker behind the grill. Negative lobe cutoff clipping will also occur earlier than the positive lobe which gets clipped much schematid by saturation.

If you end up needing a cooler bias than the circuit provides you can increase the 47k resistor try 51k or 56k for more room on the cool side of the adjustment range. Diode polarity is important, install the diodes with their stripes to the tube plates.


The normal value for a preamp cathode resistor is 1. In the right position the 2. R36 is the tail resistor that creates the relatively high voltage 34v DC in the Bassman needed for the cathode follower function of the upper cathode. Place the diode’s stripe cathode end on the power outflow side pins 4 and 6.

The 15K and 56K resistors in the original bias schfmatic form a voltage divider to reduce the voltage coming out of the bias rectifier diode. I recommend using a 1 watt resistor to reduce resistor hiss.

Notes on the tweed Bassman schematic.

Bias voltage is plotted in light blue, transformer voltage is green, diode output is dark blue and red is the junction of the pot set a 29k and 27k resistor 56k total resistance. Socket mounted V2A Load Resistor. Note the 5 volt 3 amp heater current requirements for some of the tubes.

Protect your Bassman from expensive damage. Why would anyone do this–bolt a full bridge rectifier to a tube rectifier? A cut control allows you to trim off very schemxtic ice pick highs without removing all the high frequency overdrive harmonics.

Schematoc no added coupling capacitors to change the amp’s voicing. The Vox Cut Control connects the two power tube grids with a k audio pot and 4.

See the section above if your amp has a center tapped power supply.

All of my tube sockets are military grade along with the output tubes being military grade. V1B’s cathode resistor is bypassed with a huge uF bypass cap which increases gain for all frequencies including low bass guitar freqs. The hemp cone tames the brittleness of the standard E and it just sounds freakin’ great.

If you don’t want to deal with splitting the V1 cathodes just installing the 0. The extra feedback makes the cleans cleaner and tightens up the boundary between clean and overdrive which can make it easier to control overdrive with finger technique.