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 find you run out of room and need to get a hotter bias then decrease the value of the resistor. The Long Tail Pair LTP Phase Inverter also called the cathode-coupled phase inverter is the most popular phase inverter in guitar amplifiers due to its large output voltage schematkc and sweet overdrive tone.

Here’s the schematic schemati layout to locate the components:. Diode polarity is important, install the diodes with their stripes to the tube plates. The Fender 5F6A schematic shows v as the bias voltage for tubes which would yield a significantly cooler bias. You can run the amp in standard fixed bias mode or flip the switch to a more 5E5 Pro vibe with a more ‘tubey’, round, warm and compressed tone due to it’s fluctuating cathode bias. To maximize a grid stopper’s effectiveness it should to be mounted directly to the tube’s grid pin.

Upgrade the two tiny 8uF bias circuit filter caps to 50uF to reduce 60Hz hum. The only thing I have not done is to varnish the tweed like Fender does. When I went out to look at one, I ran into the amount they cost! Preamp tube V1B gives the Bright channel guitar signal its first gain boost.

Tone Stack Fender’s 3-knob tone stack architecture is perhaps the most copied electronic circuit in music electronics.


List of Mods

V1’s cathodes are separated using two cathode resistors and two bypass caps. The JTM45 used a beefier power transformer so there’s a little less voltage sag. Less output power, small bottle tone with more power tube distortion.

The Presence control R35 and C21 removes a variable amount of high frequency from the negative feedback signal. According to Ohm’s Law, the resistance needed to create the same cathode voltage doubles when only one tube is used, so the equivalent resistance for one triode is 1.

I put a k 2 watt resistor across the standby switch Merlin mod to prevent pop and inrush current so I left off the. If you choose to modify the bright channel into the lead channel I recommend you remove the bright cap to keep the overdrive tone from getting too spikey.

It works by mixing the two phase inverter output streams together and they cancel each other out. Connect the cut capacitor from pot terminal 3 to the middle switch terminal. A 50k linear pot or trim pot offers lots of adjustment range so this circuit can bias everything from the 6V6GT to KT88’s and it isn’t picky about the AC input voltage level. There’s no added coupling capacitors to change the amp’s voicing.

The diode also drops 1. Remove the power tube grid leak resistors shown ghosted in layout above. You can even run a 6V6 and a 6L6 power tube together and bias each tube properly.

Considerations before building a 5F6A.

The ‘No Feedback’ position makes the amp break up early schematiic of like a 5E3 Deluxe. The greatest treble attenuation due to Miller capacitance occurs with the volume control set to maximum.

Signal flow shown with red arrows. If it is connected to the mid pot you will need to give the presence pot its own connection to ground. A tube rectifier will drop more voltage than a solid state rectifier. Another option to consider is changing the Normal channel’s. A solid state rectifier will only drop about 1. Another option is to add a 50KL pot between the bypass cap and ground so you can vary the amount of bypass boost with the pot. It gets great reviews and gives probably the most authentic tweed Bassman tone.


At first blush I was going to recommend not using this mod on the first stage of amplification because if the cap fails as a short it could inject high voltage into the guitar circuitry but even if this does happen the large value feedback resistor will limit the current to 18 micro amps. Heater current in amps: You simply connect both 6.

Negative AC voltage passing through the cap pushes electrons against the 56k resistor and through the diode creating a negative DC voltage at the diode’s output. You can even do this before installing the sockets in the chassis.

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

We must also remove the cathode jumper from pins 3 to 8 on the Schejatic tube socket. It’s also a good idea to turn the bias down some before installing a new set of tubes and then bias them immediately upon power up.

Click here for a hi res pdf. A speaker must be attached to the amp’s speaker jack when using the Line Out jack to prevent output transformer damage. The very nice custom lacquered tweed cab with 6″ baffle was made by John Mergili of www.

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Unfortunately, this means you can’t get the full experience. There’s a 6″ Eminence H hemp coned practice speaker behind the grill. Fender also added a 4. When the switch is closed the diodes’ low voltage drop bypasses current schematiic the tube rectifier.