RobRob Deluxe Amplifier
By Rob Robinette
Have comments or corrections? Email rob at: robinette at comcast dot net
I've had a lot of requests for a 5E3 Deluxe layout incorporating many of my favorite 5E3 mods so this is it.
The RobRob Deluxe project utilizes POTENTIALLY FATAL HIGH VOLTAGES. If you are unfamiliar with high voltage circuits or are uncomfortable working around high voltages, DO NOT RISK YOUR LIFE BY BUILDING THEM. Seek help from a competent technician before building any unfamiliar electronics circuit. RobRobinette.com DISCLAIMS ALL LIABILITY FOR INJURY OR PROPERTY DAMAGE RESULTING FROM THIS INFORMATION. ALL INFORMATION IS PROVIDED 'AS-IS' AND WITHOUT WARRANTY OF ANY KIND. See more tube amplifier safety info here.
The RobRob Deluxe amplifier incorporates the following modifications:
Lead Channel Mod Higher gain channel designed for cleaner, leaner, modern overdrive tone. This channel is very pedal friendly and really responds to boost pedals.
3-Position Negative Feedback Switch with: Normal 5E3 / No Bypass Cap / NFB for three levels of preamp gain. The "Normal" position is highest gain, the "No Bypass Cap" position is a nice middle-of-the-road gain position and the "NFB" position is lowest gain with the cleanest tone. This mod makes the amp much more versatile and offers up much more clean tone. The NFB position also works really well with pedals and effects.
Pre-Phase Inverter Master Volume allows low volume shredding and eliminates the 5E3's nasty sounding "double frequency" phase inverter overdrive distortion. With the master volume full up the preamp is just like an unmodified 5E3.
Elevated Heater Voltage for reduced hum.
Adds Power Tube Screen Resistors to protect the power tubes from over overdrive and sweetens the overdrive tone.
10% Power Switch Attenuation Circuit for bedroom level practice. When engaged, this circuit converts 90% of the amp's output power to heat. The 12 and 16 ohm 25 watt resistors must be bolted to the chassis as a heat sink to dissipate the amp's output power. This works well for true bedroom level practice.
Doubles the size of the first filter cap to 33uF to reduce hum and firm up the amp's bottom end.
Upgrades the 5 watt power tube cathode resistor to 10 watts for reliability. The stock resistor is rated at 5 watts but Fender upgraded to an 8 watt in their Edge Deluxe but 10 watt is a much more common resistor size.
Adds Rectifier Tube Protection Diodes to the rectifier tube socket for reliability. This 50 cent upgrade makes life much easier for your tube rectifier.
Adds a Standby Switch Anti-Pop Surge Resistor to eliminate switch pop and control turn-on power surge for added reliability and longer filter capacitor life.
A proven unified ground bus is used to reduce noise and hum.
Uses metal film input and V1 grid stop resistors for minimum amp hiss.
The V1 cathode resistors are split to minimize interaction between the two channels. The V1 and V2A cathode bypass caps have their own eyelet/turret for the Switched NFB mod and to make future mods easier.
Uses my favorite tweed speaker, the Weber 12A125A with 20 watt rating, light dope and standard dust cap. Ask for Weber's free speaker break-in.
You can upload the RobRob Deluxe Hoffman Board DIYLC file to the HoffmanAmps.com DIY File Analyzer and Doug will make an eyelet or turret circuit board for you. The cost should be around $18 + shipping.
Bill of Materials
You will also need a cab, speaker, power cord, wire and power and output transformers.
RCA Corporation, RCA Receiving Tube Manual, RC30.
Merlin Blencowe, Designing Tube Preamps for Guitar and Bass, 2nd Edition.
Merlin Blencowe, Designing High-Fidelity Tube Preamps
Morgan Jones, Valve Amplifiers, 4th Edition.
Richard Kuehnel, Circuit Analysis of a Legendary Tube Amplifier: The Fender Bassman 5F6-A, 3rd Edition.
Richard Kuehnel, Vacuum Tube Circuit Design: Guitar Amplifier Preamps, 2nd Edition.
Richard Kuehnel, Vacuum Tube Circuit Design: Guitar Amplifier Power Amps
Robert C. Megantz, Design and Construction of Tube Guitar Amplifiers
Neumann & Irving, Guitar Amplifier Overdrive, A Visual Tour It's fairly technical but it's the only book written specifically about guitar amplifier overdrive. It includes many graphs to help make the material easier to understand.
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