Excelsior Tremolo Depth Control

I’m glad that Fender included tremolo (and didn’t call it vibrato) on the Excelsior, but I find it a little on the weak side, especially at higher speed. This mod kit makes it adjustable.

This is a preliminary version; the final version will be on the faceplate, between and below the tremolo and tone controls.

My goal with all Excelsior mods is to do them without removing the circuit board in the upper chassis–everything has to be done from the top of the board. This limits some of the mods, but removing the board is laborious and time-consuming. Removing the board also raises the possibility of breaking wires.

Give it a listen and tell me what you think:


  1. fuenteboy says:

    sounds great Bill.
    Please let us know if and when a kit is available or a parts list.

  2. Veloket says:

    I think the depth control sounds great! I installed your tone control mod and it works very nicely. I would like to purchase the depth control when available. How difficult would it be to add a selectable power output switch or control, say to reduce power to 5 watts? Thanks!

    • bill says:

      There are a couple of ways to reduce output power, depending on whether you want to retain distortion. I’ll look at master volumes and such in the future.

  3. Veloket says:

    Basically, I’m interested in being able to push the amp slightly into distortion while playing at a reasonable volume level at home. Right now, with the Eminence 1815 installed, 1/5 volume setting is plenty loud. Also, when do you think you’ll have the tremolo depth control available? It’s awesome! Thanks!

    • bill says:

      Sorry it’s been delayed so long. I’ve been working full time just to keep up with current mods and kit orders.

  4. CraigH says:

    Hi Bill,
    Thanks for all of the great info and kits you have. Is the tremolo mod kit out for sale yet? I can’t seem to locate it. Also a question on the speaker you mention, the Eminence Legend 1518: is that the speaker that comes in the colored “Pro” versions of the Excelsior? The price difference on Music. Friend is right at $100 if you catch the sales on these, I see on eBay they go for right about $90. For +$10 one could choose a color…

    • bill says:

      The tremolo kit will be available shortly. I have all the parts, but need to shoot new video and photograph/write up instructions.

      The Pro version has the Legend 1518 speaker, so yes, you can have the speaker and color choice by choosing the Pro model.

  5. Morgan says:

    Hi Bill – I have a question for you about how this tremolo circuit works. I can’t find a similar tremolo on any Fender amp (cathode bias with the oscillator affecting both halves of the signal between the phase splitter and the power tube grids). It looks to me like maybe Fender got the idea for this trem from the old Danelectro/Silvertone 1472: http://harmony.demont.net/documents/schematics/amps/silvertone_1472.pdf

    In the “A Look Inside Fender’s Excelsior” page and in the video on this page, you refer to the tremolo as effecting the grid bias on the output tubes. My understanding of typical output tube grid bias is applying negative DC voltage to the grids, as in the common Fender-style fixed bias scheme. Typical bias-vary tremolos just use the oscillator to wiggle the negative bias voltage on the output tubes grids. What piqued my interest in this amp was that it’s cathode bias, so there is no fixed DC component on the grids to wiggle. And also, C6 would be blocking any DC voltage coming from the oscillator anyway. That really got me all riled up and confused. 😉 http://ampgarage.com/forum/files/pawnshop_excelsior_schematic_149.pdf

    So, finally, my question is this – how is this tremolo circuit working? There is definitely an AC component to the oscillator that probably gets through C6. When that oscillating AC signal goes through the R32/R33 divider, is it causing cancellation of the AC guitar signal coming from each side of the phase inverter, and thus providing a tremolo effect through signal cancellation?

    I’m finding this circuit very interesting as I’m used to tremo circuits using DC voltage from the oscillator to turn on and off a lamp, or to affect the grid or cathode bias of a pre amp or power tube. Anyway – thanks a bunch for your thoughts and great job on the depth mod!

    • bill says:

      I think it’s just bias-vary trem. There’s no signal cancellation because that would have to happen in the output transformer, where the push and pull signals meet, and the frequency is too low for that.

      When the trem is off, it’s straight cathode bias. When the trem is on, the output tubes become more conductive and less conductive, compared to their cathode-biased state, as the trem signal goes up and down. The .1uF in C6 can provide a strong signal, right down into the infrasonic range. The MOSFET is acting like a cathode follower, pulling the signal high and low, with no worries about bleed-down time. And an AC imprint of that signal shows up strongly on the other side of C6.

      By the way, I think one of the coolest things about the Excelsior circuit is how they essentially make the two pieces of coax in the armor tube act as a transmission line, using the 470K resistors at both ends to provide a fixed impedance and coupling the shield to ground with small capacitors. The designer told me it took them a while to get that feature just right.