Is my Mark IV an A or B model?


How can I tell if I have a Mark IV A or B model?

The easiest way to determine a Mark IV A from a Mark IV B model is to take a look at the effects loop(s) on the rear panel of the amplifier.

The Mark IV A models have two Series, Mono Effects Loops (NORMAL and SWITCHABLE). The Loop Labelled NORMAL stays on all the time while the SWITCHABLE LOOP is switched in and out of the circuit by either the footswitch, the programming rocker switches or the external jacks (when the Mark IV is being controlled by a MIDI switcher). If the SWITCHABLE LOOP is turned on by the rockers or external jack, the footswitch cannot turn it back off. Two rocker switches are provided so you can pre-set the Loop to come on in conjunction with any one or two modes. 

Mark IV A - 1991-1994

    • Serial Numbers: IV-0001 to Approx. IV-6000s 
    • Two Series, Mono Effects Loops (Normal And Switchable)
    • 12AT7 in the reverb tube slot (V4) 
    • No reverb foot switch on the back.
    • Older style Bronco Vinyl and LED's.
    • Smaller power transformer than the Mark IV B.


The Mark IV B models have a Series, Mono Send / Mono or Stereo Return Effects Loop that operates manually or can be assigned to any one or two modes. This Effects Loop can be used to allow the Right Return's signal to travel through the Mark IV and (if running Stereo Effects)  the Left Return's signal to be sent through to an additional amplifier (like our Simul-Satellite) for a stereo image.

Mark IV B - 1994 to 2008

    • Serial Numbers: Approx. IV-06000's to IV-13119
    • One Series, Mono Send / Mono or Stereo Return Effects Loop
    • Satellite send function with Satellite EQ switching.
    • 12AX7  in the reverb tube slot (V4) 
    • Reverb foot switch jack added on back of chasis.
    • Slightly larger power transformer than the Mark IV A.


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