Extra Bias Filter Cap Mod Reduce hum from the bias circuit. Add a Presence Control Use this late-in-the-circuit tone control to tame ice pick and tweak your tone. 5k resistor for "Light" NFB (half of normal NFB). Firm Up the Deluxe and Deluxe Reverb's Loose Low End Make it sound more like a Twin Reverb. Twist the leads of two 220k 1/2 watt resistors together (new mixing resistors) and solder the twisted end into the empty eyelet. Deluxe reverb tremolo not working on my. Richard Kuehnel, Vacuum Tube Circuit Design: Guitar Amplifier Power Amps.
Best defense against ham fisted drummers. Both channels have a coupling cap and mixing resistor feeding the reverb circuit and the V4B preamp stage. Deluxe reverb tremolo not working on laptop. Disconnecting the Mid resistor will completely remove the tone stack from the amp circuit. Since current into the output transformer is cut in half we need twice the load on the transformer secondary to compensate. This mod is already done in the 68 Custom Deluxe Reverb.
The 68 CDR is not a silverface amp, it is an almost exact copy of the 64 Deluxe Reverb Reissue with just a few valuable tweaks. The mid scoop is also flattened out. In reality this switch changes the 6V6 power tube from a pentode (5 electrodes: cathode, control grid, plate, screen grid and suppressor grid) to a tetrode (4 electrodes since the screen grid is deactivated) but by convention we call it a pentode / triode switch. Vibrato stopped working on Deluxe Reverb Reissue. It's true the Vibrolux and Vibroverb have an 8 ohm output transformer secondary where the Band-Master has a 4 ohm but that will make no difference if you connect a matching speaker. After getting these voltages I powered the amp through a bucking transformer to bring down all the voltages. It does not affect the stability of power section and no special bias considerations are necessary. Photo and mods by BobbyZ.
047uF coupling cap to the new Normal channel 220k mixing resistor installed in Step 1. It's actually pretty easy to add a Presence Control to any blackface or silverface amp with a long tail pair phase inverter. Note how V7 and V8 share the blue output transformer wire--they are in parallel so we can turn off V7 with the cathode switch. Deluxe reverb tremolo not working on youtube. The resistors are mounted next to the Bass tone pots. SPST (single post single throw) switch between the Volume pot and Input jack. In the Low position input impedance is 62k (1M in parallel with 66k) and grid stopper resistance is 33k. Now you plug it in with a 3.
Click the image to see the full size version. 7k Presence resistor mounted on the Presence pot. If present, remove the capacitor in parallel with the 10 meg ohm resistor (old modification). The tremolo circuit has three disk capacitors. Power tube screen grid is connected to either the plate in the triode mode, or the B+2 screen power supply in the pentode mode.
RCA Corporation, RCA Receiving Tube Manual, RC30. Run 6L6 Power Tubes in a 6V6 Amp A tone change with little power gain. All of the AB763 mods on this webpage apply to silverface amps that have been blackfaced. 02 Mid cap and an extra 18k resistor between the Bass pot and Mid resistor.
These work by cutting on and off the actual signal within the amp. When an AC audio signal enters a capacitor there is a slight delay as the cap fills and drains. Take a measurement with the normal 6V6 tubes so you have a baseline temp to compare to how hot it gets with the big tubes. With the switch to the right you get Normal NFB with an 820 ohm resistor. 047uF coupling cap and both channels guitar signal flow through the Vibrato Channel's. I now recommend you leave resistor R35 at far right in place (Vibrato Channel Mixing resistor). The frequency response graph on the right will change as you alter component values or move the Bass and Treble pot sliders (at bottom left).
8k Mid resistor is used in amps without a Mid pot (usually a 10KA pot). The small board at far left adds a soft start thermistor and Class X RFI noise cap to the mains line. For a big bottle amp with a 4 ohm output transformer secondary we need to connect an 8 ohm speaker. Running 6L6 tubes will stress the transformers so I don't recommend it but if you want to give it a try then you should make a change to the speaker load to compensate for the different power tube impedance. Note the cap polarity, positive + to ground because the circuit deals with negative voltage. For amps with a 100 ohm NFB Tail resistor we use 820 / 100 = 8.
To convert the Band-Master into a Vibrolux or Tremolux you need to replace the Band-Master's 4. Switch OFF = no master volume at all, ON = bedroom volume. 7k resistor here, you can chose any resistor value between the original value and 4. Disk cap numbers 1, 2 and 3 match the numbers in the schematic above. In fact, solid-state oscillator circuits tend to have a wider range. The Cool Mod adds a local negative feedback loop to the Normal Channel's second gain stage (V1B). 5k resistors for factory or "Normal" 820Ω of NFB resistance. The downside is it slightly limits how low you can set the bass. Replace the 2-Prong AC Receptacle with a 3-Prong. Set the trim pot to maximum resistance before installing so the bias will be set to coolest. 'AB763' was Fender's internal model designation for the 1963 blackface circuit. 3v heater voltage and make sure it's not 10% lower than spec (lower than 5.
For the mod you increase the V1A cathode resistor from 1. 8k Mid resistor to the center-left push-pull terminal and connect the ground to the bottom-left terminal. Like most amplifier negative feedback loops this mod will reduce distortion, tighten the transition from clean to dirt and slightly reduce gain. Blackface AB763 tone stacks with their large. However, both of these types have technical draw backs. Robert C. Megantz, Design and Construction of Tube Guitar Amplifiers. Hence, you will achieve preamp distortion earlier. Remove or clip the Stability Caps connected to the Power Tube Grids (pin 5).