A Guitar And Gear Support Forum

I completed my pedal board for my vintage 1964 Fender Vibroverb and notice the amp wasn't behaving. Was sounding muddled in the midrange when it warmed up and was presenting a non-harmonic farting tone just before edge of breakup settings. Shout out to @mozz, who is very knowledgeable and a great person to confer when faced with hidden anomalies!

Well, it is fixed and sounding spectacular!

I'll start with the hardship of this amp, is that the inclination is to keep as much original or NOS as possible AND make it a killer amp, makes replacement decisions arduous. Even more so, there are only a few ever built and mine is the 3rd made in January 1964, making it more like a prototype, where it has original components which neither match the AA763 nor the AB763 schematics. Meaning, this amp was probably experimented on by Leo Fender and Freddie Traveres (who wants to undo that?).

Current maintenance included:
- Replacing the 1990 Sprague filter caps (installed in 1992, replacing the OEM) with brand new F&T.
- Swapping the 100k 1w load-split carbon resistors in the filter section (undoing Leo's work), for NOS 220K 1w carbon resistors.
- Replacing the NOS late 70's Phillips 6L6WGC output tubes (one of the two was failing bad), with my last matched pair of the same.
- Biased the new tubes.
- Replaced the GT12AT7 inverter driver tube, with a 1960's Raytheon 12AT7 (each tube half was more balanced, providing more symmetry at output).
- Replacing the October 1963 oil in paper cathode caps, with new electrolytic caps.
- Checking all the blocking caps for leaks and all the solder joints for integrity.
- Changed the original negative feedback inverter to ground resistor from 100 ohms to 75 ohms, which is midway between what was on the amp and
what was called out in the schematic.
- Added grid 1K5 snubbing resistors to the output tubes' pin #5 (was like the AA763 design, but less punishment f the tubes and aligned to the
AB763 schematic.

I keep all the original parts in a bag, for eventual resale.

The amp currently sports a Weber 15F150 speaker (a clone of a mid-60's Jensen) with the original JBL in a box for safe keeping. Dead quiet at idle and more dynamic and 'V' shaped scoped tone that before. A lot more range of clean, edge of breakup and breakup tones. Does pedals a lot better than before.

Oh I'm sure that amp will surely show you a pedal's true colors. The Raytheon 12at7 is probably a black plate. Glad it's back up to par.

mozz wrote: ↑Mon Jul 22, 2024 3:11 pm The Raytheon 12at7 is probably a black plate.

100%. Nasty black plates and yellow silk screen label. It measured an even 24-24 per triode in the EICO merit test. The scope verified it.

andrewsrea wrote: ↑Mon Jul 22, 2024 4:24 pm

mozz wrote: ↑Mon Jul 22, 2024 3:11 pm The Raytheon 12at7 is probably a black plate.

100%. Nasty black plates and yellow silk screen label. It measured an even 24-24 per triode in the EICO merit test. The scope verified it.

I have no idea what any of this (and most of the OP) means but I can appreciate the knowledge and expertise needed to pull of the restoration. Great job all-around!


Is that the original foot switch? Did it still work?

tlarson58 wrote: ↑Mon Jul 22, 2024 10:06 pm
Is that the original foot switch? Did it still work?

Thanks, Tommy and good eye for detail! Yes, to the right of the pedal board is the original footswitch to activate the reverb and tremolo. All in proper working order.

This amp has a cool story, in that it first belonged to my childhood friend's older brother who bought it new in 1965 and quit playing electric guitar in the 80's. My friend ended up building an owning a professional recording studio, to which I helped the construction and then the maintenance of the equipment. After a few years of operation, he bought two MCI 16 track 2" tape machines from the Record Plant in NYC. The actual machines that recorded John Lennon's 'Imagine.' Needless to say, they were wrecks and needed constant attention. I'd get calls at 1AM to come fix them in the middle of recording sessions. Since he and I were childhood friends, I never asked a dime for any of my contributions to his studio build and upkeep. Which compelled he and his brother to give me that Fender amp, to which I had no idea how rare and collectable (since Stevie Ray Vaughn used two).

andrewsrea wrote: ↑Tue Jul 23, 2024 11:43 am

tlarson58 wrote: ↑Mon Jul 22, 2024 10:06 pm
Is that the original foot switch? Did it still work?

(since Stevie Ray Vaughn used two).

Is this amp responsible for SRV's guitar sound on the song "Cold Shot"?

Very very cool. Great story and info about that amp! What an awesome piece of gear.

toomanycats wrote: ↑Wed Jul 24, 2024 6:36 am
Is this amp responsible for SRV's guitar sound on the song "Cold Shot"?

The one and only. Most of Texas Flood was done with primarily a stock Vibroverb with a JBL E-130 (ceramic magnet), an occasional Dumble and Marshall Club and Country (for clean-cleans).

When I have the original JBL D-130 installed, I can get that tone. The problem is with that speaker, that is the only tone you get. It doesn't do pedals well and from '1' to '4' on the volume, it is clean and tinny, especially with a Fender single coil.

This?

tlarson58 wrote: ↑Wed Jul 24, 2024 8:16 pm This?

Yep. Except this guy got a few things wrong. The biggest is how many were made. He said "around 1,500" which I think is the total number of model year Blackface amps 1964 amps made. There were only around 4 to 6 people assembling amps back then and they were all hand assembled.

I consulted with John Sprung (wrote many books on Fender Amps and still runs a vintage parts store) and he said there are no official records, but his estimate was less than 100 Vibroverbs ever made. He said one prototype made for the 1964 NAMM, held in July 1963 and a few per month. Advanced orders were sparse from the show and low-rate production started in August to fill those orders. Production was said to have ceased in September or October 1964, with demand for the Deluxe Reverb, Super Reverb and Twin Reverb eclipsing the Vibroverb, thus consuming the factory resources.

Additionally, I personally have paid attention to the tube charts (picture of tube layout glued to the inside of the cabinet) of any Vibroverb which came for sale, which tells what year, month and what number of that model that specific amp was for that month. The highest month production number I have ever seen once was '8', made in June of 1964. The next most common highest I've seen is '4'. My estimate is 6 per month average (ramping up production, then ramping down) so, 6 per month times 15 months = 90. John Sprung's estimate of around 100 is on the money.