Vibroverb
clone project
transplant from a Silver Face Fender Bandmaster Reverb head 1974
as a chassis and circuit donnor.

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(Update, December 2008)
Now running with a GZ-34 rectifier tube and two Genalex KT-66 Gold Lion power tubes,
no tube in v1 (the unused clean channel) and a 5751 in v2 (preamp of the reverb channel).
If you want MOJOTONE, try the KT-66 in replacement of the 6L6, they are beautiful valves.

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Clic on pictures for more definition.


 

I'm not trying to build an exact replica of the "1964" Fender Vibroverb used by Stevie Ray Vaughan in his to short life.

The Fender Vibroverb combo amplifiers with a 15 inch speaker where only produce for a short period of time during 1963 - 1964 and thoses highly collectible amplifiers already reach crazy price of more than 3,000.00 USD, I even saw one on E-Bay at $ 6,000.00 USD !

So for a poor guy like me, the only solution is to build one, the hard way.

I bought this Bandmaster Reverb head 1974 to start the project. The chassis front panel layout is the same on a Vibroverb than a Bandmaster, except that in this case the 1974 the Silver face Bandmaster had an extra knob for the middle tone control. This potentiometer will be remove and the 3 lasts pots (the Reverb, the Speed and the Intensity controls) will have to be move in the previous hole of the chassis. With this mod, the original Vibroverb faceplate fit exactly on the Bandmaster chassis, they both mesure the same lenght at 23.50 inchs.


Click on pictures for a larger views.

The chassis upside down out of the head cabinet, showing from left to right, the power transformer (PT), the choke, the output transformer (OT) and in the middle of the six tubes the reverb transformer. Note the five original filters capacitors (caps) with their brown sleaves, they are 33 years old. I will change them for security reasons, theses capacitors filter the AC high voltage out of the main transformer into softer DC voltage and carry about 425 Volts with enough amperage to kill you (even unplugged) or can make serious physical dammages if you don't know what you're doing ... BEWARE Read how to discharge capacitors.


Close up of the original Mallory capacitors

After 33 years of "loyal" service, it was time to do a "caps" job,
thoses new fine filter capacitors are F&T brand made in Germany.
There where nothing wrong with the output transformer(OT),
but I wanted to increase the bottom end performance and headroom
so I chosed the exclusive Allen/Heyboer transformer TO40MT,
this one is a nice upgrade that fit in the same holes of the stock OT.

 


The chassis with his new "Vibroberb" Black face plate,
less the "middle" potentiometer that I removed as the "death cap"


As I receved it.

This picture is very interresting and I don't know why, but by comparing this curcuit layout whit the Fender layout, I found two places where the capacitors are missing ... ??? I don't know yet if the amp is working, UPS broked tree tubes during transport, the big ones (and the most expensive one) the rectifier tube (5U4GB) and the two power tubes (6L6GC) so I can not try it untill I receve my unexpected new tube order. The seller told me that the two 6L6 where fresh new tubes. Thank UPS, you are taking good care of our merchandise !

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Message from Jimy on Hoffman Amp forum. http://www.el34world.com/Forum/yabb2/nph-YaBB.pl?num=1183218991/0
Unless my eyes deceive me, those caps are indeed missing. It looks as if someone tried to do a cap job on the amp at some point and either didn't know what he was doing, or had some innovative ideas about how to do things differently. Those white caps look like replacements and, yes, the two missing caps need to be there to correctly bias the cathodes of 1/2 of V3 and 1/2 of V5. I'd imagine the amp would still work but sound "not quite right." Also, since one of the missing caps belongs to the tremolo circuit, that might be the answer to your tremolo problems... though I suspect something else may be going on here.

Thank you Jimy


Clic on any pictures for a larger view.

Ok, I only had one capacitor on hand, so I add the one near the tremolo section.
And NO ... it diden't resolve the tremolo problem.


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July 3, 2007

Meanwhile, waiting for some parts on order, I deceded to make some modifications :

I changed the FILAMENTS wiring with new cloth wires to correct the mistake Fender used to do during thoses years (now the wiring is in phase).

"Also, when filaments are hooked up in parallel (this includes almost every tube amp ever made for guitar), it is important that they be wired in phase. For example, the same wire that goes to pin 7 on one tube must go to pin 7 on the other tube. The wire that goes to pin 2 on one tube, goes to pin 2 on the other tube".
Ref.: TUBE AMP TALK FOR THE GUITARIST AND TECH - By Gerald WEBER  - Page 20

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Friday, July 6, 2007, I findly receved my Weber 15 inchs speaker and I was very anxious to try it.

Bad news .... it sound terrible with lot of distortion on low notes. I suspected immediatly a defective speaker, or vibration comming from the baffle (only two screws where there, one on each side) or from the speaker that was install (temporaly) with only four screws. 

Then I deceded to check how the amp is bias. So I study the Lord Valve paper on biasing power tubes. As describe, I took mesurement of the plate voltage on pin 3 of the power tubes = 425V. Then I mesured the Voltage across the two 1 ohm resistors = 24 mV or .024 Amperes, so I have 425V X .024 Amp = for a static plate dissipation of 10.2  WATTS, way to cold, in fact the 6L6 GC tubes should run just under the maximum of 23 WATTS.

The problem come from the 1974 Bandmaster design who is a Balance type bias adjustment. Of course, the two power tubes are "well balance" each tube are set to a similar reading of .024 mV on each, but  there is no way to trim up or down the voltage with a potentiometer. If I understand well how a Balance type bias work, I have to replace the fix 470 ohms bias resistor to set the voltage up to around 35 mV instead of my actual 24 mV reading. I look in my bin and no .... such resistors in stock ... :-(  
I need a larger resistance value to increase the voltage on the tubes;

"A smaller value will give you more negative voltage in the bias circuit. More negative voltage means less current flowing in the power tube.
A larger value bias range resistor will drop the overall voltage of the bias circuit.
Less negative voltage means more current flowing in the power tube".  Ref.: Hoffman Amp

but I'm planning to convert this useless Balance wiring by the regular Black face bias design (tubes are now available as match pair).  Hoffman Amp supply good informations on how to do this conversion, but I have to wait "again" for parts on order to start this mod.

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July 12, 2007

Good news .... now the amp sound pretty good with lot of punch and became well alive with no more ugly and bad crossover distortion, I did some work and converted the Bandmaster bias balance system to a common bias system as use on the blackface, I set the bias voltage to 35 mV and the plate voltage is 425 V. 

Lot of work have been done today, I replace the "roach" or the opto-isolator, this fix the tremolo that was not working, but the tremolo don't sound to good, I can ear the tic tic throw the speaker, does someone have an idea to make it sound better ?  As you can see on this picture bellow, there are not to many original capacitors left ! Other than the tremolo, the amp now really sound "creamy". I never heard a real Vibroverb live with a JBL 15 inchs, but I can say that the Weber California ceramic 15 inchs speaker with a paper dome sound awesome ... :-))

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August 15, 2007

All the Solen capacitors are gone ... replaced by Mojotone oil capacitors. I'm trying to find what is causing the amp to lack "gain" and to distort early (volume at 4 ... !). These caps are a little better sounding than the Hifi Solen, but there is a unknow problem, need help please   info (at) jeangodbout.com

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Here you can see my homemade Telecaster replica
with my Vibrolux Reverb amp.


I made this Tele replica body with a single peace of pine 2" thick (finish to 1.750"), the neck is carve using soft curly maple on a 10" radius with jumbo triangular frets, (no truss rod ... hummm .... I used a fix carbon fiber bar instead) the result is fantastic, it diden't move at all and the tonal transfer is simply much better than a regular truss rod who is a tone brake or a tone killer in my opinion).
The first run of the Fender "Broadcaster" in 1950 had pine body and no truss rod, but no high tech carbon fiber stiffeners.
Don't try this with eastern hard rock maple, it will make a banana neck very quick ... 
Western big leafs soft maple is much more stable and often come curly.
Pickups are Fender Custom shop No Caster, Bakelite pickguard, old style flat head screws, vintage bridge with brass saddles.
The guitar look like a solid body .... but it's almost a Thin line since a drill many holes and then I cover the back with a .110 " pine back. The guitar weight only (about) 5 pounds on a cheap bathroom scale, it's light and really vibe !

The Amp is originaly a Silver face Vibrolux Reverb 1973, beat up .... so I made a new cabinet with Baltic birch plywood, new rough brown tolex, and of course a caps job with nine new potentiometers, new set of tubes, new reverb tank, new Weber speakers (2 ten inchs in the cabinet and a twelve inchs in the extension cabinet), new Brown face plate with matching knobs, new Oxblood grill clothe and my unique molded Fender flat logos that I made with polyester casting resin and a new tube chart ... !

NEXT -  the Vibroverb Cabinet (page 2)
 

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Fender Silver face Bandmaster Reverb layout (AA 1069)

and the objective :

Fender Black Face Vibroverb layout (AB 763)
Schematic (AB 763)

Weber version layout (6A40)

NEW : Trainwreck Express 4-4-0

NEW : Fender Princeton Reverb clone

OVERDRIVE HRM BLUESMASTER - DUMBLE clone amp

 Tube condenser microphone

John LENNON Gibson Les Paul Junior Custom clone or style

Rosewood Telecaster clone (by far my favorite guitar)

Terry KILGORE tube scam with the complicity of George METROPOULOS (METRO AMP)
+ Marshall JTM45 clone

Jumping into modernity, Parker Fly Style guitar

Experimenting pickups winding

My Fender Vibroverb clone amp

Fender Tweed Deluxe (5E3) clone

TWIN Tweed Deluxe or 5E3x2

Fender Telecaster clone building page

Fender Stratocaster clone guitar

Here a funny Telecaster with a double personality

Oh yes ... I also build acoustic guitar, here my take on a Martin clone (000-42 Style)

Front 1   -  Front 2    -   Back  -  With Jacques MICHEL

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Link : JP Strat-o- Blogster