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Tag Archives: pedal steel

  • Modifying a Fender Bandmaster Reverb

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    What does the pedal steel player have in common with the armies of tube disciples, weekend warriors, and every other six string mother post 1958 Link Wray? Nothing. Guitar Amp doctrine presumes everybody wants to distort. Granted, 50 million Elvis fans can't be wrong, but players often wanting clean tone are left out of the discussion. Many choices and advice for those who are searching for clean sound can be confusing. Technical advice coming out of the HiFi world or well-meaning advice from endless forum jockeys debating how Carol Kaye got that bass sound from a super reverb, can be exhausting. From what I have found as the amp tech here at Main Drag Music, a good guitar amp makes a terrible HiFi amp and a good HiFi amp makes rather lifeless guitar amp.


    Steel players usually desire a tight amp with plenty of clean headroom without it being stiff. Not just steel players though. I am constantly in conversations with songwriters, jazz, and country players wanting to hear that weirdo chord they came up with resolve to a Gm7, without it being muddy. A correctly working tube amp will be able to dial in a clean sound on low and intermediate level volumes. Once you open the gates and push the amp into clipping, then it will distort, compress, and yes, sing.  More on that in my next blog on harp amps and pentodes. Seriously!


    Recently, I had a fun project in the shop. A Fender Bandmaster Reverb head had been fitted into a custom 1x15 cabinet. The player wanted it cleaner and tighter through the wide tonal range of the instrument. I started with choosing a better output transformer than the stock one, and switched over to solid state rectification. Solid state rectifiers reduce sag and increase voltage. Yes, voltage sag can bring the soul in a tube amp Chester Burnett style, but today's alchemy is not that simple. Having more voltage and a faster power supply is the foundation we wanted for the output section. The output transformer I used was a Mercury Magnetics Beauty, which gave us a low end strength and tonal balance. This transformer gives the Bandmaster no restrictions on the back end and lets us actually "hear" the subtle and not so sutle "sound" of the tubes. A good output transformer breathes effortlessly with the power tubes and the speakers. It magnetically couples the two with invisible lines of flux casting out some harmonically rich AC voltage to the speakers. Transformers to me are undoubtedly magical, like AM radio, Springsteen's Nebraska, or driving all night in the Jersey Pine Barrens in a 1968 Cutlass, alone.


    Next, I wanted to clean up the preamp. I removed the first preamp tube, which was a 12AX7 for the reverb channel, and swapped it with a lower gain 12AY7. In most guitar amplifiers the preamp section is designed around the notable dual triode, the 12AX7 (ECC83). A dual triode is a type of vacuum tube with two separate gain stages in one tube. They share their glass envelope and heater but you have two independent stages of gain, EQ, vibe, taste, etc. The amplification factor of a 12AX7 is 100. When you plug into the input jack of your amp, a weak signal gets immediately amplified by the first tube in the circuit. From there it moves to the tone controls and then the volume control, which is only an attenuator.  Then the signal goes right back into the same tube, then onward through the rest of the preamp.  This first tube in the circuit is crucial to your tone and how you distort. Other tubes with less gain can be substituted in the first preamp stage without modifications to achieve cleaner tone. A lower gain tube in the first position will be softer and less likely to clip. Once you have distortion in the beginning of that chain, that distortion will remain throughout. A different tube type will still give you plenty of volume and help keep it clean.



    Here is a video of the finished modded Bandmaster and a list of different preamp tubes with their amplification factor. These are all substitutions that you can experiment with, for a 12AX7. I also advise against using a 12AT7 which many people do, as they tend to be very microphonic in the first stage. Also if using a 12AY7, get a new old stock one. The vintage 12AY7 will actually work (unlike the new ones) and summon some serious spirits, just like the croon of the pedal steel itself.


    Tube 12AX7, amplification factor 100

    Tube 5751, amplification factor 70

    Tube 12AT7, amplification factor 60

    Tube 12AY7, amplification factor 45

    Tube 12AV7, amplification factor 40

    Tube 12AU7, amplification factor 18


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