Bradley Labs Guitar Amplifiers

Operation Manual

Front Control Panel


Note on the Tone Stack:  The Iron Horse tone stack controls are revolutionary in their ability to tailor the amp’s sound to different guitars. The controls offer the player the ability to cut or boost different frequencies.  Think of “Lo” as the “more power” or boost option and things will become much more intuitive.   



Hi:  This is the ‘clean’ channel.  If you are looking to achieve nice clean tones with plenty of headroom, plug in to the Hi input.   With the Hi input  cranked, you’ll still get nice break-up but it will be much more controllable.


Lo:  This is the Overdrive channel. The trick to getting a clean sound out of this channel is to use the guitar’s volume.  Even on modest volume settings (especially with Humbucker guitars) you will start to get break up.  Simply open up the volume a bit, and then back down the guitar’s volume to where you have a clean sound.  Then if you need to boost for a solo or get some hairy distortion, crank up the volume on the guitar.  Having the ability to simply move your guitar volume to get your powerful distortion and lead sound is a whole new experience for most players.  The Iron Horse excels at this ability.


A note on distortion:  The Iron Horse is a Non-Master Volume amp.  Searing, sustaining, Brown-Sound distortion happens at around 1:00 – 4:00 especially on the “Lo” input..  This is extremely loud, so take proper precautions and use the amps Power and Configuration settings to lower the volume appropriately.  The distortion is coming from the power tubes; there is no pre-gain stage to distort the signal until the "Quench Mode" kicks in at about 5:00 where the output begins to reduce but the distorion and sustain very much remains.

Tone Stack:

Treble / Mid / Bass: 
Vary these controls as needed.  Start at 12:00 on all knobs, and then dial in your tone.


Pre Shelve:  This is an extremely subtle setting.  Keep the setting on “Lo” to start with and then experiment with the settings once you have all the other settings dialed in.  You’ll hear a slight bottom boost on the “Lo” Setting, this is a good place to start.


Drive: Select “LoZ” to double the amount of gain.  You’ll get a big 6dB boost in the signal that will help with early break-up.  This switch works on both the Hi and Lo input to help increase gain.  On the HI input, you’ll get a nice smooth overdrive sound, on the Lo input you’ll get fat, early distortion with an enhanced low-end.  Leave the switch on “HiZ” for a bit more clean head-room.


Post Shelve:  One can hear a slight mid-to low bump by playing with these settings.  Start on Medium and toggle between Hi and Lo settings for reference points.  For some sounds it is helpful to bump up the Post Shelve setting to add a bit of high to the “Lo” settings on the Post Coupling Switch.


Post Coupling:  This dynamic control bumps the overall bass output.  Hi sets it to the minimum bass output, Medium bumps the output quite a bit, and then Lo bumps it to the maximum.  This control is extremely powerful and can seriously fatten up single notes, even with single coils. Set the Bass Control to 12:00, and then select the Lo/Med/Hi selection.  Use the bass control to tailor the overall bass frequency to taste.  


Volume: A single control that allows both “Clean” amplification as well as “Crunch and Sustain” In operation the Volume control operates as a Pre Amp Gain control, used on any single channel amplifier up to about 80% CW. Going beyond 80% on to full CW continues to increase preamp gain, but now starts to reduce power amp gain, or Master Volume. The combination of the Guitar Volume control, which is an extension of the Pre Amp Gain control, the LO/HI input selection, the LoZ/HiZ Drive selection and the front panel Volume control with the Quench mode allows any level of sound and/or style one could accomplish with separate Gain and Master Volume potentiometers (see graph below).  We like to call this our "volume quench" function.

Brite:  This selects a small value capacitor that connects across the wiper to top terminal of the Pre amp Gain section of the Volume control. It effectively allows high frequencies to pass through with no attenuation at low volume settings.





A note on the Post Shelve /  Post Coupling / Brite Switches: 

These three switches are designed to work together.  If you have an extremely bass-heavy guitar, you can back off the Post Coupling switch to medium, and brighten up the highs by switching the Brite switch to “Hi”.  For a bright guitar like a Strat, a Set the “Post Coupling Switch” to “Lo” and the “Brite” to “Lo” for a fatter sound.  Use the Post Shelve Switch to help as a second stage fat boost or cut depending on your Post Coupling Setting.  This switch helps compensate for the extremes of the other switches and helps fatten the sound or bump the low mids if need be.  Like everything else use your ears! 


The Character section of the amplifier caters to the personality of the speaker used.  You can literally tailor the signal to the speaker to get the best performance available.


Presence:   This is used to balance high and low frequencies.  It is a good way to smooth out a trebly guitar or add a bit of top end to dark humbuckers.


Feedback:  This control allows the speaker to “ring” more than a conventional guitar amp.  It provides the ability to get a bit more liveliness from the speaker and the player can feel just a bit more responsiveness when digging in and hitting notes or chords. Maximum clockwise rotation will appear to almost increase volume.  Think of increased settings as ‘opening up’ the speaker.  This is truly a feel adjustment, the speaker will feel more reactive when playing at higher settings.  For clean playing, you’ll get a ring that is quite unique to the Iron Horse.  For the heavier rock stuff, dial back the feedback to tighten up power chords.


Configuration:  This sets the power tube configuration and influences power and volume.    Pentode will have the most volume, Triode will have the least amount of output and Ultra Linear will be slightly more powerful than Triode.  For lower volume playing, use the Triode switch, you’ll be able to drive the amp harder at lower volumes. 



The Output Section is the true heart and soul of the Iron Horse.  Using these controls along with the tone stack, you can attain nearly any sound you are looking for.


Bias – This selects self/Fixed bias:

More output power is obtained when in the fixed position as no power is wasted in the cathode resistor needed for self bias. There is a time constant associated with the “self” position, so high volume sustain should show a difference in fade just like tube rectifier.  This is an extremely subtle difference so go by your ears.


Power:  Selections


4AB1:  Use this setting for the most clean-headroom and most volume.  It utilizes all 4 power tubes in Class AB configuration.  You will get the most overall depth of sound using this setting.  It is great for cleaner settings and for running pedals in front of the amp.  Run a multi-effect chain into this setting and your tone foundation will be amazingly strong and balanced with tons of bottom end available.


2AB1:  This is the half power setting utilizing two power tubes.  You can dial in sweet break-up tones, snappy, punchy rhythms and all out tonal mayhem by playing with this channel.   Though this channel uses only 2 power tubes, it is still incredibly loud.  Do not dismiss this as half power by any means.


1A1:  This setting utilizes a single output tube and will give you the earliest distortion.  Use the class A setting in conjunction with the Triode configuration for Maximum early break-up at lower volumes.


Impedance:  Match this selection to the speaker rating of the cabinet.  When using the 4AB1 setting, you can gain an additional 10 watts of output power by doubling the Impedance selection on the Iron Horse to the Speaker rating.  For example if the speaker rating is 4 Ohms, select the 8 Ohm.  Also, use your ears; you can get some interesting sounds by playing around with this setting and intentionally miss-matching the switch to the speaker cab.  For example, try setting the Impedance to 16 Ohms when using a 4 Ohm speaker; you’ll get a slight reduction in volume as it works the amp a little harder to get distortion.



Diode:  Select this setting for a Solid State rectifier.  This will provide a less spongy feel.  You’ll get a bit more power and evenness.  Good for Jazz and more clean type sounds, or a more aggressive overdrive tone.


Standby:  Set the switch in the middle for standby mode.  The amp will stay powered but no sound will come out of the speaker. Mode switching can be accomplished “Live” without switching into Standby.


Tube:  This setting utilizes the Tube Rectifier.  Digging in to notes will yield a sag typical of tube rectifiers; you’ll get a bit of compression compared to the Diode switch.


Line:  Select “On or Off” to turn the amp on or off.  It is best to switch the amp to Standby mode before powering on or off.  The Pilot light will light up when the amp is switched to on.


No damage will result if the Iron Horse is accidentally operated without a speaker!