Other Amps

The Excelsior Project


I'm going ahead with the upgrading of the Fender Excelsior.

I look forward to posting changes and findings and discussing it with anyone who would like to.

Link to the schematic:



So, as I posted in the "first reactions" thread, I found this guy to have no head room and kind of a paper-slappy kind of fuzz vibe, although aesthetically, it's super cool.

First couple things I'm going to try is of course, tubes and a different speaker.

Here's the OEM tubes and the bias sitting at 30, which is pretty hot by my understanding.


Put JJ's in. It Definately added a little headroom and a sweeter tone.

Cranked, it was like a cool Fender with a Fuzz Face dialed in for light fuzz. Lol, pretty cool for Neil Young chords and Black Crowes solos. :P

Not what I want it to do though.

To add, that was with a Paul w/ P90's.

Tomorrow I try plugging into a pair of 12" Jensens and bring my 6196T to work.

Will see what Bill M has on his site tonight as well.


I'm looking forward to your mods. I have no business inside of an amp, but it will give me some ideas for my Excelsior. I'm going to get a new speaker and tubes for starters. The deep/bright switch has to go too.


Thanks for tutorial.I am interested in the Excelsior.


Been waiting for a thread along these lines...

Should be good, a nice Weber 15 or JBL! :D

I would be ditching the switch too, get a pot in there!!


Agreed on the pot. and a bias pot. I have easy "cheap" koff access to Jensens. Probably going that route, the C15N.


Put an EH AY in V1. It's the Pigat-Vane mod, haha. It brightens and tightens the tone. The accordion input has the best impedance.


An Electro Harmonics 12AY7? I'll see if I have one. ...or another AY7.

Care to expound on your accordion input input? :P Thanks Geoff!


The accordion input seems to have a nice input resistor which matches average pickup impedance. You can check the schematic.

Here you got a schematic which people can actually read:


If you're creating a bias pot, maybe you can incorporate a little analog meter panel on the back for direct bias reading.


So, had time to look at some stuff today. And my buddy Dwayne, who is an amp guy, came by to look and listen w/ me.

I hooked the Exce(selsior) up to the 2x10's in a Vibrolux and the 2x12's in a Twin to see how much of the fuzzi-paper was speaker vs. amp.

It seems to be amp. It's just loose and fuzzy. Although, the 2x12's improved headroom a little and the presence or sweetness of the high's, the low end was loose and farty. Again, little to no clean headroom. Pretty over driven by 4 on the dial.

Dwayne and I looked at the bias on his much cooler probe that has mA and Plate Volts.

350 V and 31.2mA. Hot.

I had blown up the schem and we looked it over. We have ideas. Will post more later.


Put an EH AY in V1. It's the Pigat-Vane mod, haha. It brightens and tightens the tone. The accordion input has the best impedance.

– Geoff_Vane

Put an EH AY in V1. It's the Pigat-Vane mod, haha. It brightens and tightens the tone. The accordion input has the best impedance.

– Geoff Vane

Can we just plug that in and go, or does the amp need to be biased afterward?


That is a pre amp tube so no bias adjustment needed.


Yep, plug it in and have a listen. It's a 100% reversible safe mod. Paul likes the Excel, but it was a bit floppy with buckers when crancked. I arrived with a AY at the Eindhoven gig and Paul plugged it in the Excel right away, live on stage. He thought it improved the performance really well. I let him keep it for future giggery.


A PS Note:

One of the things I hit my buddy Dwayne about was why the Exec is rated at 20W w/ 2 6V6's and the Exce is 13. So we went over some schem stuff and it looked to Dwayne that they where "choking" the Exce down in these points:

We notice that the yellow values are doubled in the Exce. So, a future thought may be to try the Exec values.

Of course, the Exec is using an entire 12A- tube as the inverter and the Exce is only using 1/2 a tube. So, that Exec has a more efficient inverter that could produce a bigger wave before distorting. Exce is using a "long tail" inverter?


Geoff, definately have to try the AY and see if it tightens things up. It is a floppy amp.

Thought: As the AY has a lower amplification factor, it should over drive sooner, so wondering about that for trying to achieve headroom out of this guy.

hmmmm....have to look at schem for where that volume control is pumping juice through.


Well, V1 takes in the guitar at the right impedance and it compensates after the tone circuit. It's two halves of one valve used for two functions.

I'm no schematic expert, but this is my quick guess. Seems the AX drives the end circuit quite hard and thus causes early floppiness. The AY is somewhat milder and therefore the volume can be crancked more before crunch sets in. I had expected the AY would just act the same as lowering the volume knob, but it didn't.


I did the AY mod to the V1 in my Ampeg J20 (basically a Fender Brown Deluxe). It does lower the amplification factor a bit, but it didn't drop the headroom much if at all, but it did increase the volume sweep (which is why I did the mod). But we may be comparing apples and oranges, so YMMV.


Yeah, comes into V1-A and brings it to line level, then runs through the tone stack and into V1-B to compensate for loss through the tone stack.

Geoff, your saying that V1-B looks to be driving into the inverter quite hard?

I notice a 5E3 does use a 12AY in V1 w/ an 820ohm to bias and and "V2-B" is the same as the Exce w/ an AX7 and the 1.5K to bias. The Exce using 3.3K on an AX in V1-A. Definate difference there!

Read on the Bill M site that both sections, pre and power, where set up really high gain. So, maybe just the AY or bias it down a bit would help out. Definately will do the AY and post findings.

More to come from my "Dwayne Session" too. We rapped some other cool and interesting stuff (for the only moderately informed :D that is).

Thanks for any and all input guys!


Does this change in tone control look like it would work?

I notice the 470K resistor on the tone switch. Would replacing the switch and resistor w/ a 500k pot sweep between the two sounds, or would it just act like a switch once you turned the pot up enough. Anyone?


I hate to admit it, but I feel like a complete moron after reading this thread. I definitely should've taken electronics in school...


Ha! No worries FJR! I've only been at it a year with really digging into tube amp guts.

Check out Gerald Weber of Kendrick amps and his DVD's. Great jump start!


I think the tone pot is a smart plan. You need a linear one. It would enable to sweep from dark to bright or stop in-between.

FJR we can teach you things here!

Look at point s1-a. This is where the guitar sound sits. Set the switch to bright, then the bright sounds will crawl through point WJ18, R9 and C2, towards the power tubes.

R29 and C19 are trying to kill the bright sounds by pulling them to ground (the little triangle below C19), but R8 blocks them. R8 is like a narrow funnel, so the bright sounds are more likely to go towards C2 and the power tubes.

Set the switch to dark, then the guitar sounds lands at point WJ20. Now R8 is not really helping the bright tones. R29 and C19 draw the bright tones away into negative ground which acts like a kitchen sink; whoosh down the drain with the bright sounds.

The bright sounds that want to escape towards C2 are blocked extra by R8 now, because point WJ20 lies under R8 and not above it like WJ18 in the bright setting.

Megabutter has a brilliant plan. Take a 500k potmeter. (almost 470k like R8). A pot has three feet. The outer feet just connect to a 500k resistor inside the pot like Megabutter has drawn in his modified image. The middle foot of the pot connect to a sweeper. Megabutter drew an arrow, which is the sweeper. It can sweep the guitar sound from point WJ18 to point WJ20. This means when you turn the pot to its most outward positions, you'll get exactly the same situation as with the switch: either full bright or full dark.

Beauty of 'butter's plan is the the in-between position, where R8 is split by the sweeper in 250K towards C2 and 250K towards the ground. Now the bright sounds will half go up to C2 and half disappear to ground. This should sound more neutral and help people who think bright is too bright and dark is too dark.

Now, it could be the C and R values are picked by Fender in such a way that the true middle position between dark and bright is not at halfway the pot. That could mean a very small tone sweep for instance. But I think it may work perfectly because the other R values above the pot and below the pot are both 22K. That looks like a balanced situation to me.

You never get a true neutral sound, it will always be voiced. But that adds character. The R9 & C2 is a high pass filter, so it kills dark tones. The R29 & C19 is a low pass filter, so it kills bright tones. This means drifting between two voicing filters. I can imagine people saying bright and dark are both over the top. The filters can be re-voiced too, but using a potmeter is worth trying.

It would be possible to create a bypass switch, to avoid filtering. Go from WJ19 to R23 with an extra 22k to avoid instant mega crunch. But try the pot first. It's more exciting.


BillM (from the Blues Jr mod fame) is going to offer both a pot mod for the tone, and an on/off switch for the tremelo.

Sounds like he's waiting on parts, so he can start offering kits. His testing has had some pretty good results with this amp.

Some nice options for those who want to mod this amp.


Thanks for another great post Geoff!! Great description and the linear pot suggestion (hadn't thought of that 8-o ). I'll draw up a schem w/ that bypass, I like that idea a lot.

Regarding hooking the switch up w/ another 22k: I see that it would keep the resistance similar to what's on the original tone switch. I see the where that would keep the signal more even. But, if we just lifted it out of the circuit, we'd get a boost through the volume pot and therefore a little more "crunch" from hitting V1-B harder? W19's contact point is the start of a little voltage divider isn't it. OK, I'm seeing it. :D Dang! That sounds like a new footswitch idea!! :D

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