A Look Inside Fender’s Excelsior
This is a preliminary page for Fender’s Excelsior amp. The Excelsior will benefit from some mods and upgraded components.
Here’s a look inside the Excelsior, the left (looking from the back of the amp) side of the power section. Apart from it’s “pawn shop” vibe, the Excelsior is modern inside. It includes an NTC thermistor to control inrush current and the full wave bridge diodes are individually bypassed by noise suppression capacitors.
The two large white sand-cast resistors are “sag” resistors, to simulate a tube rectifier. In addition to the main fuse, there’s a heater fuse and a soldered-in plate supply fuse on the output tubes.
This board feeds the output tubes. They’re cathode-biased, as you might have guessed from the 13 watt output rating. The sockets are ceramic. The output jack is rather inconveniently located behind the output transformer.
The flexible tube that connects the preamp chassis to the power chassis is standard, electrician-grade stuff. The tube is steel.
In the preamp chassis, the input voicing is done right on the jack board. There is no voicing on the guitar input, padding (reduced signal) on the mic input, and a fairly heavy treble cut on the accordion input. The mic input is somewhat like input 2 on a typical guitar amp: twice as much resistance, but unlike most Fender amps, it retains high impedance on the mic input. The accordion input is capacitor-coupled, which cuts signal strength and attenuates frequencies. I found it fairly useless for guitar.
The signal goes through the ferrite at the left to eliminate RF noise. Since there are only two amplification stages, they’re very high gain. Fender chose 220K plate resistors for the gain, plus a high value for the first stage’s cathode resistor. The result is kind of un-Fender-like.
The volume control and tone switch sit between the two stages. “Dark” is a heavy treble cut. Bass is the same at the Bright or Dark settings, but Bright activates a treble bypass cap that boosts highs. The contrast is too great between the two settings; this amp definitely needs a tone control.
The tremolo circuit is a conventional low-frequency oscillator that varies the grid bias on the output tubes. The tubes are cathode-biased, but there’s a combination of grid- and cathode-bias when the tremolo is active. The power transistor on the board is a MOSFET that drives the grids. The phase inverter is a conventional cathodyne circuit, much like that found in the Princeton Reverb or Tweed Deluxe. The signals go through individual, shielded wires to the grids of the 6V6s.
The sockets are attached to the chassis and the 12AX7s are shielded. The amp is equipped with Chinese 3-mica tubes, which aren’t too bad.
The underside of the panel is straightforward. No circuit board-mounted components except the input jacks. Lots of room for mods!
Overall, the Excelsior is a loud amp and even with the two high-gain stages, it’s uncomfortably loud for home playing before you get crunchy distortion. It’s going to need some modification to allow distortion at more reasonable volume.
The Excelsior has pretty strong mod potential.
I’ve already tested it with a one-knob tone control that uses the stock bright and dark settings as its upper and lower limits. I’ll be offering it as a kit. The control itself is the easy part. The harder part is a good-looking faceplate that covers the screw holes and slot. The slot also requires some filing to clear the shaft of the tone control.
I’ll also have a kit for a tremolo on/off footswitch.
The stock 12AX7s are not too bad for inexpensive Chinese tubes, but feel free to experiment. The stock 6V6s are just adequate. I prefer JJ 6V6s because the large plates improve bass response and they sound better overall. A better output transformer will help, but an upgraded speaker is a better investment, at least at first.
The stock speaker is not particularly efficient and has a characteristic tone that dominates the amp’s overall tone. An Eminence Legend 1518 is far more efficient–louder, with more consistent tone, better bass. It’s probably the most cost-effective 15-inch speaker you can find, too.
The Excelsior is clean at moderate volume. The best way to get overdrive tone at low levels is with a pedal. There may be other ways to get more gain out if it; I’ll post more as I experiment more.
Here’s a video of my Excelsior with a single-knob tone control, with and without the Eminence Legend 1518 speaker:
My take: The tone control really helps tone down the treble harshness. The Legend 1518 has classic tone, greatly improved lows, and a much more refined midrange. It’s also dramatically louder than the stock speaker.