RAT Valve Amps
- RAT Fender Blues Junior V3 Handwired -
I Specialise in Modifying and Handwiring the Fender 'Blues Junior' Valve Guitar Amplifier.
This is your 'One-Stop-Shop' if you have a Fender Blues Junior (FBJ). I keep all Spares 'In Stock'. If you have a Problem with your FBJ, I can fix it for you -or- Fully Handwire your Amp -or- Modify your Amp.
Twin Rectifier and SAG
- Most 'RAT' Amps use the 'Twin-Rectifier' System -
The Mains 'On/Off' Power Switch has 3 Positions.
'Centre' Position is AMP OFF.
'Back' Position is AMP ON, using the Valve Rectifier.
'Forward' Position is AMP ON using the Silicon Rectifier.
The Only Reason for Fitting a Valve Rectifier in a Modern Amp is to Induce Vintage Style 'SAG'. The Amp does not require a 'Standby' Switch as long as it is Switched 'ON' to the Valve Rectifier Position.
All Amplifiers use a Rectifier to convert the Raw AC Voltage from the Mains Transformer into DC Voltage. The Amp Circuits Need DC Voltage to work. If, for example, you Hit a Power Chord on your Guitar, the Amplifier Circuitry Suddenly Demands a Large Dose of Power from the Mains Transformer. Silicon Diodes are Extremely Efficient and can convert the Raw AC into DC almost instantaneously, to Feed the Amplifiers Needs. Valve Rectifiers are a Different Story. Generally Speaking, they can't Cope with Sudden High Demands of Energy and they 'Starve' the Amp of Power until they can catch up with the Demand - This is Called 'SAG' - and it Sounds GREAT!
The typical sound Produced by an Amp using a 'Silicon' Rectifier would be -
- Attack - Sustain - Release - Decay -
Using a 'Valve' Rectifier, the Sound will be Closer to -
- Attack - Swell - Extended Sustain - Release - Decay -
To your Ears -
In 'Silicon Rectifier' Mode the Initial Note Attack is Sharp and Crisp - Like a Modern Amp.
In 'Valve Rectifier' Mode the Initial Note Attack is almost Soft and Laid-Back with Longer Sustain - Like a Vintage Amp.
It is OK to Switch Between Rectifiers While the Amp is Running.
This System works equally well with 'Class A' - 'Class A/B' - 'Single Ended' - 'Push Pull' - 'Cathode Bias' and 'Fixed Bias' Amp Designs.
Note - The main function of a 'Standby' Switch is to Allow the Valve 'Heaters' to warm-up before the High Voltage Hits the Amplifier Valves. Using a Valve Rectifier the High Voltage is delayed (to the rest of the Amp) as the Valve Rectifier warms-up. A 'Standby' Switch can still be fitted, and used, but it is not a requirement when using a Valve Rectifier.
Fender Blues Junior Handwired
- RAT FBJ Handwired Combo with OPR -
The ultimate FBJ. The Stock Amps Main PCB and Valve Holder PCB has been removed and replaced with a RAT Custom Made Eyelet Board and Valve Board, then 'Point-to-Point' Handwired into the Amp Chassis. The 'Solid State' Reverb has been replaced with true 'Valve Powered Reverb' using a Valve, High Voltage Reverb Driver Transformer, 'Accutronics' Reverb Tank and On/Off Foot-Switch. The Reverb now sounds WAY Better. All Tone Capacitors are 'Orange Drops', Power Resistors are 'Metal Film' and the Pots have been replaced with 'Alpha' Parts. Includes 'Bias Adjustment Control', 'Variable Boost' Foot-Switch and 2x Speaker Outputs. The Original 'FAT' Switch operates from the Control Panel and can be used in conjunction with the 'Variable Boost' Foot-Switch. The Handwired Amp Sounds Stunning with Plenty of 'Clean' Available and Loads of Gain/Overdrive if you want it. NO Background Noise. On the EL84 Amp the Power Output can be increased to 18~21 Watts RMS.
Optional Extra - 'Twin-Rectifier', you can select 'Valve' -or- 'Silicon' Rectifier.
I can supply a New Handwired Amp -or- Modify/Handwire your Amp.
v2, 3, 4 and Tweed Amps can be fitted with 'OPR'.
Available on ebay (Prices are Higher) -or- Direct from me.
Please 'Contact' me for Full Pricing Details -or- your Requirements.
- FBJ v3 Handwired Tweed with OPR using EL84 Power Valves -
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- FBJ v3 Black Handwired with OPR using EL84 Power Valves -
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- All Modifications -
1. - The Stock Fender Main PCB has been removed from the Amp and replaced with a RAT Custom Built ‘Eyelet’ Board and Valve Board which is then fully ‘Point-to-Point’ Handwired into place using all New 'Alpha' Pots and Switches. All of the ‘Tone’ Capacitors on the RAT Board are ‘Orange Drops’, along with ‘Metal Film’ Power Resistors.
2. - 'Twin-Rectifier' - Select Silicon -or- Valve. This is an Optional Extra available at additional cost.
3. - Smoothing Capacity has been increased for 'Tighter Bass' -and- A 'Safety' Resistor fitted so that the Amp can not hold a Lethal Charge when switched off.
4. - The Stock FBJ uses a ‘Solid State’ Reverb Drive and Recovery System. This has been replaced with ‘Valve Reverb’. The Reverb Tank has also been replaced with an 'Accutronics' unit. About 30% of the Components on the Fender PCB are used in the ‘Solid State’ Reverb Circuit - All of this is now Gone.
5. - All Stock Blues Junior Amps run a 'Hot' Bias setting with NO Bias adjustment control. This makes the Amp sound Harsh and also causes other problems when changing the Power Valves. The RAT Eyelet Board has a 'Bias' adjustment control. This will increase the 2x Power Valves life and makes the Amp sound better.
6. - Full Lead Dress - All Transformer and Heater wires in a Valve Amp must be tightly twisted or they will induce 'Noise' in the Amp Circuit. Twisting all of the wires and placing them in the correct location keeps the Amp ‘Quiet’.
7. - Variable Boost Footswitch - Connects to the Inner Rear Chassis Panel - (Button 1) Switches the Internal Boost Circuit On-or-Off. The Footswitch is fitted with a Variable Boost 'Level' control (from Zero-to-Max) and gives a HUGE Boost to the MID Frequencies and Harmonics. (Button 2) is Reverb On/Off. There are RED ‘LED’ Indicators on the Footswitch powered by an internal Battery.
8. - The Input Jack Socket on all Stock Blues Juniors is a Problem. This has been replaced with a Jack Socket that can be easily changed in about 5 minutes (if you ever need to change it).
9. - Modified Tone Stack - The Factory Tone-Stack does not allow total tone control, The Controls sweep in a 'Preset-Range'. The RAT Modified Treble, Middle and Bass Controls will sweep from 'Zero-to-Max' on each Frequency.
10. - Star Earth - The Stock Earth/Ground Paths on the PCB are a Mess and run all over the place in different directions. With the removal of the PCB this problem has been eliminated and the Correct ‘Star’ Earth (method) used. This allows all required Earth Paths to be in a logical order and kept as short as possible to eliminate any Noise ‘Loops’. There is NO Background Noise from this Amp.
11. - 2x Speaker Output Sockets - The Correct Speaker Output Load Impedance is 8 Ohms. If required, the Amp will happily run 4 -or- 16 Ohm Loads. This will not Damage the Amp.
12. - Half-Power Switch - Reduces the Amps Output Power to about 8 Watts. This is an Optional Extra available at additional cost.
13. - RAT User Manual detailing all of the Changes.
14. - All Amps are PAT Approved.
SubZero T20R - (FBJ Clone) -
I am no longer modifying these Amps - The Following is for Information Only.
If you Own a Stock T20R (NOT the RAT Modified Amp) I suggest you STOP using the Amp and get it Safety Checked ASAP. Some of the Amps I have seen are LETHAL and there is a serious threat to the user of receiving an electric Shock. The two worst problems relate to the Rear Panel Mounting Screws being too long, one of them can touch the Mains (240vac) Power Fuse on the lower rear panel of the Amp, the other drives itself into the Mains (240vac) On/Off Power Switch on the Top Control Panel of the Amp. NOT Good. The Stock Amp has NO Internal (HT and Heater) Fuses, this is a recipe for disaster.
If you don't have one of these Amps - DON'T BUY ONE!
This Amp is a Copy of a Fender Blues Junior (FBJ), The Cabinet Looks a Bit Different but other than that, it's an FBJ. If you need a Circuit Diagram for the T20R, you can get it on the Fender Website, The Circuit is Identical and 99% of the Component Ident numbers on the PCB are the same. The Amp is Sadly let down by VERY Poor Attention to detail during Assembly. Every Nut, Bolt, Screw and Fastener in the Amp is usually Loose or has already fallen out. The First thing I did when I got one of these Amps was to collect all of the 'Spare' parts from the Speaker Magnet. I think if you purchased a Stock Amp and took it directly to a Gig, it would be 50/50 that the Amp would Survive the duration of the Gig....Not so Good. However, once all of the 'Loose' Issues were corrected (and the RAT Modifications done), it is a Good Sounding Amp (No real Surprise as it's a Copy of the FBJ). There are a stack of 'Minor' Issues that need to be corrected on the Amp in order to assure it's Reliability, nothing Serious, just the usual Mass Production short cuts (Poor Quality Capacitors, Underrated Resistors, Cheap Switches, No Fuses). Most of the Important Components (Transformers, Valve Bases, Valves, Speaker, Pots and Sockets) are usually decent Quality.
- Additional RAT Features and Modifications -
1. - 'OPR' - Output Power Reduction (Power Scaling).
2. - The Amp is completely Stripped and then rebuilt, making sure that all fasteners are Tight or Thread-Locked as required.
3. - Twin Rectifier System - The Mains Power Switch is replaced with a '3 Position' Switch offering the Standard 'Silicon Rectifier' -or- 'EZ80 Valve Rectifier' Operation. Center Position of the Switch is 'Power-Off'. The Valve Rectifier gives the Amp some Great 'SAG' - The Silicon Rectifier gives the Amp a Nice 'Tight' Sound. There is No 'Standby' Switch, this is not required Providing the Amp is First Switched 'On' to the Valve Rectifier Position.
4. - The HT Voltage (B+) is Spot-On but the Heater Voltage is WAY Too High - I have corrected that problem and the Heaters now run at 6.3vac, as they Should.
5. - I have done Several Modifications to the Power Supply - Increased the Smoothing Capacity for 'Tighter Bass' - Fitted a 'Safety' Resistor so that the Amp can Not hold a Lethal Charge when switched off - All of the Main Power Supply Resistors have been replaced with 'Wire Wound' or 'Metal Film' Components.
6. - All of the 'Tone' Capacitors have been replaced with 'Orange Drop' Parts. This gives the Amp much better definition. The Tone Controls Sweep from 'Zero-to-Max' on each Frequency.
7. - Full Lead Dress - All Transformer and Heater wires in a Valve Amp must be tightly twisted or they will induce 'Noise' into the Amp Circuit. Twisting all of the wires and placing them in the correct location does make this Amp quieter (No Background Noise - Buzz+Hum).
8. - The Standard Input socket is a Problem. It is PCB Mounted and made from 'Hard' plastic. The first time you 'trip-up' over your Guitar lead, you will destroy the input socket. It is then a Major job to replace the socket as the Amplifiers PCB must be removed. The Socket has been replaced with a Quality part that can be easily changed in about 5 minutes (if you ever need to change it).
9. - The Stock Amp is not Fitted with HT and Heater Fuses - It is Now.
10. - Preamp and PI Heaters Converted to 'DC' - The 2x Power Valve Heaters are 'AC'. This Stops any Hum and Buzz and also allows any Make of Valves to be used in the Amp.
11. - The Amp has been converted to 'Auto-Bias' - Class A/B. You will NEVER need to Re-Bias the Valves. Output is 15 Watts RMS - 22.5 Watts Peak Power.
12. - Boost Footswitch in Metal Housing with 3m Lead. A 'RED' LED Illuminates when the 'Boost' (Fender 'FAT') Circuit is Active.
13. -Full RAT User Manual detailing all of the Modifications.
14. - All Amps are 'PAT' Approved.
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