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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Turn on the Power Switch then wait around 15 seconds for the tube heaters to come up to temp and for the pop resistor to charge the filter caps enough to prevent a current inrush which is what causes the pop. Gain at 82Hz is down by less than a tenth of a dB. The complexity of Weber kits ranges from very simple to extremely complex. When a positive voltage signal arrives at the upper grid the reduction of blocking negative electrons on the grid allows electrons to flow from its cathode, through the grid, to its plate.
The mod connects a preamp’s second or third gain stage plate back to its grid through a 22M to schemaitc resistor and.
Prowess Amplifiers – Fender – Schematics – Bassman 5f6a – Schematic
Chart is from the Duncan Tone Stack Calculator. It is much more cshematic to add to an existing amp so for modding an existing amp I recommend the Type-3 master volume.
It crosses the knee of an imagined curve green for a V screen and a 0V grid.
It indicates that the grid voltage can swing from 0V to -8V, so the bias is warm and input headroom is 2. Consider using metal film resistors if you don’t care if the circuit board does not look period correct.
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. For more detail schemtic how amps and tubes work see the How Tube Amps Work page. This schsmatic little circuit cannot load the transformer properly to run speakerless. This mod is an extremely easy to add local negative feedback loop that can be used to tune the overdrive tone of any high gain preamp.
My amp’s heater circuit measures 6. Voltage sag is the dynamic voltage drop that varies with current demand and causes compression of loud and quiet notes.
The cab is a 5E3 combo but it’s vented and sized so it can also be used as a sealed back extension cab scuematic can’t seal the back and run the 5E3 due to heat buildup. High voltage AC from the power transformer enters the circuit at the.
Many Fender tweed amps use a 25uF bypass cap which will still boost all guitar freqs. I schematci this mod to my 5F6A Bassman and it works great.
When the switch lever is pushed inward the scematic tubes are in normal, high power pentode mode. If at full 56fa pot movement max hot bias you still need to bias hotter then reduce the value of the 27k resistor–try 24k or 20k. Less output power, small bottle tone with more power tube distortion.
The ‘No Feedback’ position makes the amp break up early kind of like a 5E3 Deluxe. This grid voltage is generated by the R36 tail resistor. This size bypass capacitor is rare but it does not need to be an electrolytic. Why would anyone do this–bolt a full bridge rectifier to a tube rectifier? See more tube amplifier safety info here. This prevents a current surge when you close the Standby Switch. You can use this circuit that’s based on the Marshall JCM to create an adjustable bias tap without using a power transformer with a dedicated 50v bias tap.
I really shouldn’t call this section “mid-production” because these circuit tweaks seem to have been made early in the 5F6A production run because they are seen in almost every original tweed Bassman and Twin chassis photo available.
List of Mods
Connect the cut capacitor from pot terminal 3 to the middle switch terminal. The input resistor on the Hi input jack sets the amp’s input impedance and acts as the V1B grid leak resistor. No power tube cathode resistor bypass capacitor was installed. Higher wall voltage can lead to high amp voltages. These modifications reduce midrange scoop for less insertion loss. KT88’s like more plate voltage than the and 6L6 so plugging in a solid state rectifier into the rectifier tube socket will raise the plate voltage by about 10 to 20 volts and put the big tubes closer to their sweet spot.
The larger resistors will run cooler which will make them generate less hiss.