There are a handful of different ways to approach a Vibro-Clone project, each of which will produce a different end result. So before you start, you should define what it is you hope to end up with, how much money you're willing to spend, and how much time you're willing to spend. The broad definitions of Vibro-Clone possibilities can be summed up as follows:

Note: Costs are "your" price for parts only, and do not include any labor (since you'll be the one doing the work).

The "Bare Bones Budget" Vibro-Clone. $350 This Vibro-Clone will be done for the lowest cost possible. Component compositions used will not be like the originals. Nothing will be replaced that doesn't HAVE to be. The amp won't be accurate from a cosmetic standpoint. This is for a "Head Only" project, "No Cabinet". This is a project that can be completed in a half day. The tone will be good, but not exactly like a real Vibroverb.

The "Player" Vibro-Clone. $400 This Vibro-Clone will cost a little more than the Budget model. Accurate "internal" component compositions will be used. This will include recapping and giving it a new power cord. Does "not" include recapping the Coupling or Power Supply Caps. This amp will still use the stock Output Transformer. It won't be accurate from a cosmetic standpoint. This is for a "Head Only" project, "No Cabinet". This is a project that can be completed in a day. The tone will be a little closer to a real Vibroverb.

	The "Close" Vibro-Clone. $850 This Vibro-Clone will be moderately priced. Accurate "internal" component compositions will be used. This will include a full recap and giving it a new power cord. This amp will get an inexpensive Vibro-clone Cabinet. This amp will use a vintage JBL or Jensen 15" Speaker. This amp will still use the stock Output Transformer. The external amp cosmetics will be close. This amp will use average NOS tubes. This is a project that will take about a week. The tone will be pretty close to a real Vibroverb.
	The "SRV" Vibro-Clone". $1000 This Vibro-Clone will be moderately priced. Most component compositions inside & out will be accurate. This will include a full recap and giving it a new power cord. This amp will get an inexpensive Vibro-clone Cabinet. This amp will use a vintage JBL or Jensen 15" Speaker. A much larger than stock Output Transformer will be utilized. The external amp cosmetics will be close. This amp will use good NOS tubes. This is a project that will take about a week. It will have more bass & clean headroom than a real Vibroverb.
	The 99.9% Vibro-Clone (Like Mine...) $1250 This Vibro-Clone is expensive, but still less than a boutique. 99.9% accurate component compositions inside & out will be used. 99.9% accurate external cosmetics will be adhered to. 99.9% accurate internal design and lead dress will be done. 99.9% accurate paper wound Output Transformer will be used. 99.9% accurate high end cabinet with all hardware will be used. 99.9% accurate newly reconditioned vintage 15" JBL D130F. 99.9% accurate high end NOS tubes will be used. Expect this project to take 4 to 6 weeks. 99.9% accurate tone as compared to a real Vibroverb.

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In order of importance:

Note: The parts necessary are dependent on which "class" of Vibro-Clone you want to build. See categories above in "Important questions to ask yourself before you start ?"

1. An early "Silverface" Bandmaster Reverb head (preferably). A 1968 or 69 are the best platforms for this project, because the later the model, the more you have to change to blackface & clone it. Second choice would be a Pro Reverb, which allows you to use the same speaker and cabinet. Last choice would be a Super Reverb... While a Super Reverb "can" be used, they're really good amps in their own right, so they should only be chosen if they're already basket cases or as a last resort.
2. A heavy duty grounded 3 conductor power cord if the amp you're starting with doesn't already have one. Black if you prefer, gray if you want the original color used on the Vibroverb. (This is optional, but HIGHLY recommended for your own safety).
3. For all but the "bare bones budget" model, you'll want to recap the amp which will require the following:

   	Poly Tone Caps (Either Mallory 150 or Sprague Orange Drops). 6 - .1 3 - .047 1 - .02 1 - .003
   	Ceramic Disc Caps (Buy high tolerance, not Radio shack brands). 1 - .001 2 - .01 1 - .02 *Don't replace smaller one's unless visibly damaged.
   	Foil Coupling Caps (Sprague Atoms are the best). 7 - 25uf-25v
   	Foil Bias Supply Cap (Sprague Atoms are the best). 1 - 25uf-50v
   	Foil Power Supply "Doghouse" Caps (Sprague Atoms are the best). 3 - 20uf-500v (Next largest available size won't fit). 2 - 70uf-350v (Some people use 450v's).

4. Resistors for blackfacing and cloning. Note, you should also measure out and replace any existing resistors that have drifted  more than 10-15% beyond their original value. Note, resistors that are soldered into the card can't be measured accurately, they need to be de-soldered to get an accurate measurement. Note, the original Vibroverbs used Carbon Composition resistors. Newer metal film resistors can be purchased more cheaply, but they have a someone clearer tone that isn't as warm as Carbon Comp.

   	Bias Circuit Resistors 1 - 100k ohm - .5 watt 1 - 82 ohm - .5 watt 2 - 220k ohm - .5 watt 1 - 27k ohm - .5 watt 1 - 470 ohm - "1" watt
   	Negative Feed Back Loop Resistor 1 - 47 ohm - .5 watt
   	Bass Potentiometer Resistor  1 - 6800 ohm - .5 watt *(Only necessary if removing the Trem channel Mid pot).

   5. "3" Pin, 10K, Linear, Bias Potentiometer. (This is optional and only necessary for complete historical accuracy). The Silverface "4" pin bias balance pot can be wired for blackface use. The only source I'm aware of for "3" pin bias pots is Fender, they use them in their reissue amps.

   6. 15" Speaker. You can use either a vintage JBL D130F Alnico, a Jensen C15N ceramic, or a CTS 15" ceramic if you want to make the amp historically accurate. Otherwise, any 15" guitar speaker capable of handling at least 40 watts will do. I personally like the JBL best because of its alnico magnet that causes the speaker to have a smoother breakup and the natural addition of "compression" at stage volumes. The ceramics are better for a cleaner tone with more headroom. Additionally, if the speaker you use is already blown, Ted Weber, owner of Webervst does an excellent job of reconing and restoring them back to original condition. 

   7. Cloth Wire for redressing the amp's wiring back to blackface specification. (THIS IS COMPLETELY OPTIONAL). I did this on my amp, which you will see pictures of the before and after later on in this FAQ. This takes a LOT of time, patience, and attention to detail to do it correctly. I did it just to see if I could recreate the same lead dress that Leo Fender did from the Factory back in 1964. It's also a great way to quiet a noisy amp by dressing the leads the way they were intended by the original designer. But it's also a great way to screw up! If you mis-wire just ONE wire, you could end up chasing your tail for a loooooong time to find your mistake. This process is definitely NOT RECOMMENDED for the faint of heart.  But if you're as stubborn as I was, here are the lengths and colors of the wire necessary to rewire a complete AB763 Vibroverb. Note these numbers don't allow for much waste, so if you're not being very careful with measurements, you might want to pad the quantities by a couple extra few each.

   	#18 Black - 8'
   	#20 Brown - 8'
   	#20 Red - 8'
   	#20 White - 5'
   	#20 Blue - 10'
   	#18 Green - 10'
   	#20 Yellow - 16

   8. Output Transformer (Optional). You can use the original OT if you're using a Bandmaster Reverb or Pro Reverb chassis. But if you're using a Super Reverb you'll have to get an 8 ohm replacement. If you want to build the SRV model, you'll need a Twin Reverb OT. If you want to build a 99.9% Vibro-Clone, you'll need an original spec paperwound Vibroverb OT, which can be bought from Larry Rogers of Roger's Amps in South Carolina.

   9. Faceplate (Optional). For this, you need to decide if you want to keep your mid control on the Tremolo channel or not. If you're "keeping" it, you "can't" use a real Vibroverb reproduction plate. You'll have to either keep the original silverface plate, or you can use a reissue blackface Super Reverb faceplate, or you can get one of the "Vibro-Clone" faceplates that are currently being made by a few different sources. 

   10. Cabinet. You can get an inexpensive cabinet from many suppliers. You can get one with most of the hardware like tilt back legs and a logo for a little more. Or if you want a premium cabinet that's original down to the very last detail, you can do like I did and have Larry Rogers of Roger's Amps in South Carolina build it for you. I can personally attest that he does EXCELLENT work. (See my pics furthur down in the FAQ).

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Reconing

	JBL D130F's are particularly hard to have reconed because JBL has stopped carrying the reconing kits for this particular model. Ted Weber of Webervst is the only person I'm aware of that has the proper materials to do this right. He's actually had his private run of vintage spec materials commissioned just for this purpose.
	Ceramic Jensen C15N's and CTS 15's are fairly easy to recone and can be done by just about any competent reconing shop including Ted Weber.

Electronic Parts

These can be found from several sources including Clark Parts, Mouser, Mojotone, Hoffman Amps, NBS Electronics, and many others.

Tubes

These can be found from several sources including KCA Electronics, NBS Electronics, Triode Electronics, and many others.

Cabinets

My personal favorite for the great level of detail as well as turn around time is Larry Rogers of Roger's Amps in South Carolina. But there are several other sources for quality cabinets including Mojotone and many others.

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This is where we separate the men from the boys, or should I say the historically-accurate-anal-retentive-screw-counter-perfectionists (of which I am a proud member), from those which are perfectly happy with a functionally working facsimile of a real blackface amp.

Does going through the hard work and sweat of replacing all the wiring in your amp with cloth covered period correct wiring and making sure the lead dress twists meet a perfection standard beyond even what Leo's own assemblers ever created make the amp better tone-wise? I can't really say... But what I can say is that after taking on this monumental task, my amp is pretty much dead quiet and blackface-like in tone. And the act of taking on such a labor of love definitely "makes the amp your own". What did your mother always tell you...? "Anything worth having isn't easy...". 

Well, this wasn't easy, but I'm definitely glad that I've had the experience of walking in the footsteps of those long gone assemblers from Leo Fender's illustrious Blackface Era of amplifiers.

      

BEFORE < - > AFTER

(Click each Image to See Enlarged Chassis View)

Blackface Lead Dress

	Use the Layout Diagram to determine the proper color wire for each location. Use #20 or #22 gauge wire in all locations except for the ground wire coming from the doghouse and the heater wires. For those, use #18 gauge.
	Make your twists "numerous" and "tight" in any location on the Layout Diagram where you see wires "grouped". This includes wiring coming off of the pots and the bundle that comes from the doghouse along with the wires that come from the bias pot.
	Drill 1/8" holes in each location shown on the Layout Diagram, on the "upper" circuit card (not all the way through both). Dressing the wires through these holes will greatly reduce the "cluttered" look of your wiring as well as reducing noise in the amp from crosstalk of adjacent wires.

  

BEFORE < - > AFTER

(Click Image to See Hi Resolution Circuit Card View)

 

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Blackface Ground changes

The grounding scheme of silverface amps changed primarily in two locations, the first being that of the power transformer and doghouse 70uf-350v ground tap near the bias pot. Silverface amps combined the two at one ground pad, while the blackface era amps separated the two by about 1 1/2" giving them both their own grounding pad on the chassis.

The second change was in the doghouse itself off of the 20uf-500v capacitors. Instead of grounding each 20uf with it's own ground tap, the blackface era amps chained the negative ends of the capacitors together with heavy ground wire and had one single ground tap coming off of the 20uf on the end of the circuit card that was attached to the brass grounding strip near the normal channel's treble pot.

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Power Tube Circuit Remove the 2000pf (.002uf) ground suppression caps connected from pin #5 grids of each power tube to ground.

(Click Image to See Power Tube Parasitic Cap)

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Bias Supply Circuit Change the 4 pin bias pot out with a 3 pin 10k Linear bias pot from Fender (as used in the reissue amps). Then follow the wiring scheme as shown ion the Fender Layout Diagram. If you don't want to swap out the pot, you can alternately use the wiring diagram designed by Aspen Pittman. Remove the large silver cap to ground that was on the old 4 pin bias pot. Install a 15k resistor from pin #2 of the bias pot to the metal casing of the pot. Change the single 100k on the circuit card, which is connected to pin #1 of the bias pot, to two 220k resistors. Change the 50uf-70v capacitor on the small bias supply circuit card near the pilot lamp to a 25uf-50v. Change the 1.8k resistor on the small bias supply circuit card near the pilot lamp to a 470 ohm "1watt" resistor.

 

BEFORE < - > AFTER

(Click Image to See Hi Resolution Bias Pot View)

 

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Reverb Circuit Remove the 2000pf (.002uf) ground suppression cap that goes from the reverb input RCA jack to ground. Ensure the resistor and capacitor pair coming off of pin #8 of the Reverb Driver 12AT7 are 25-25 & 2.2K. If there's a capacitor on the 12AT7 tube itself between pins 3 & 8 and 1 & 6, remove it.

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Phase Inverter Circuit Ensure the coupling cap coming off of the 12AT7 inverter pin #2 is a .001 NOT a .01. Ensure the grid resistors coming off of the 12AT7 inverter pins #7 and #2 are 1M NOT 330k. Ensure the plate load resistors coming off of the 12AT7 phase inverter pins #1 & #6 are 82ohm and 100k respectively, NOT both 47k.

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Negative Feedback Loop If it exists, remove the 25pf cap that goes across the 820 ohm resistor coming off of the wire connected to the Ext. Speaker RCA jack.

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Heater Wiring At the pilot lamp, you may find two 100 ohm resistors to ground. And looking at the AB763 diagram, you'll notice they aren't there. You SHOULD NOT remove these. Their purpose is for a ground reference on the secondary heater tap of your Power Transformer. Older power transformers had a built in ground center tap, while newer power transformers did not. If you remove these, you're likely to induce a great degree of 60 cycle hum, so don't.

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Tremolo Ensure the capacitor resistor pair coming off of the Tremolo 12AX7 pin #8 are 100k & 25uf-25v NOT 100k & 5uf-25v.

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When recapping your amp you have lots of choices, way more than I'm prepared to discuss in this section. But Sprague Atom caps are commonly considered the best for the Power Supply filter caps in the "Doghouse" and the Cathode Bypass caps used "inside" the chassis (the 25-25 caps).

Ceramic caps normally don't need to be replaced unless they become microphonic (tapping on them with a non metallic object while the amp is on will cause sound to come through the speaker), or if the capacitor looks cracked near the lead entry points. If you do replace them, make sure to use high grade close tolerance ceramics, not the cheaper types found in places like radio shack.

For the tone caps "inside" your amp (the non-ceramic caps that aren't the Cathode Bypass caps mentioned above), you have two choices which can greatly affect the tone of your amp.

	Polypropylene - These caps yield a very clear warm almost audiophile tone and typically come in an axial lead configuration. (Leads exit the bottom of the cap causing the cap to stand up off of the board). Sprague Orange Drops are "Polypropylene" rated at 600v
	Polyester - These caps yield a slightly darker vintage "brown sound" tone and typically come with a radial lead configuration. (Leads exit the ends of the cap and allow the cap to lay flush on the circuit card). Mallory 150's are Polyester rated at 400v

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The Doghouse The resistors in the doghouse should match the Fender Schematic 220k, 220k, 1k, and 4.7k. The capacitors in the doghouse are the hardest working parts in your amp and if/when they fail, they usually create a dramatic fireworks show. So it's typically a good idea to replace them. The values for these caps are three 20uf-500v and two 70uf-350v

  AFTER "Coming Soon"

BEFORE < - > AFTER

(Click Image to See Doghouse View)

 

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Vibroverb design changes

	Removal of the mid pot (which is optional), requires the shifting down and rewiring of the volume, treble, and bass pots. Additionally, the bass pot gets a 6800 ohm resistor that the original didn't have to compensate for the tonal changes caused by the removal of the mid control.
	Change the 100k Negative Feedback Loop voltage divider resistor to a 47 ohm. This is the one which comes after the 820 ohm resistor connected to the Ext Speaker lead (the only resistor on the board mounted horizontally).
	The Output Transformer used in a Vibroverb was typically a paper wound 8 ohm load model, this one will yield more clean head room and more bass response than a Bandmaster Reverb OT. Optionally you can use an original Bandmaster Reverb OT, but your clean headroom will be lower and the amp will distort sooner. If you're using a Pro Reverb, the existing stock transformer should be sufficent. If you're using a Super Reverb, you'll have to change out the OT because a SR transformer only expects to see a 2 ohm load. Your only other option is to have your speaker reconed with a 2 ohm voice coil load. If you're building an SRV Vibro-Clone, then you'll want to use a Twin Reverb output transformer. This will increase the clean headroom even more over the original Vibroverb OT as well as giving the amp an even greater potential bass response because of the added iron mass.

 

Vibroverb OT < - > Super Reverb OT

(Notice the Size Difference) 

(A Twin OT is even Wider than the Super Reverb OT)

 

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Biasing can be done in a number of different ways, many of which are valid. But I've found that my favorite way is simple, effective, very accurate.

1. Before you ever turn the amp on, set your bias pot to the middle of it's range, turn all your control pots to '0', and put the standby switch in the 'ON' position. (This would be leaving the switch in the same position as the power switch 'OFF' position). Then connect a "dummy load" to your Speaker Jack. I personally just use an old speaker that a wrap in a towel to muffle any noise. But you can also use an 8 ohm 200+ watt resistor connected to a 1/4" phono jack too. (Just don't use your brand new 15" speaker for this purpose, noises that can be created by an unstable amp could damage the speaker).
2. Set your DVM for Negative DC voltage measurement and connect the positive lead to the center pin of your bias pot (the one that has a lead going to the 220k resistor pair on the circuit card). Connect the negative lead to one of the power transformer screws. Then power on the amp and try to adjust the bias pot to get a reading of -44vdc to -50vdc. Now you've got the amp bias "ballparked". Note: if you can't adjust the amp to this range, you either have a component in the amp that's drifted too far out of spec or a wiring/component mistake. You may be able to change the 15k resistor on the bias pot to a different value to compensate for the difference, but you really should find out what is causing the problem instead of using the bias pot resistor to fix the symptom instead of the problem.
3. Now, power down, put the positive lead on pin #3 of one of your power tubes while leaving the negative lead on the power transformer screw for a ground. Turn the amp on again and notate the DC voltage reading. Then power down, move the positive lead to pin #3 of the other power tube and repeat the process. You now have your Plate Voltages. Note: Make sure these two readings are either identical or at least very close. If they aren't, then again, you may have a component drift problem or a component/wiring mistake. 
4. Now, go to the Download section of The Vibro-Clone Workshop and download the "Plate Load Calculator" from Duncan Amp's. Launch the program (you'll need to have Microsoft Excel), and put the plate voltage you notated in the previous step into the spreadsheet where it calls for it. See the next step for the "dissipation rate" to complete the necessary information to run the calculator.
5. The two tubes that you have a choice of in the Vibro-Clone are the original spec 6L6GC or for a little darker tone and slightly earlier breakup you can use my favorite, the 5881/6L6WGB. The dissipation rates for each are as follows.

   	27v @ 70% - 6L6GC
   	23v @ 70% - 5881/6L6WGB

   The resulting value you see listed in the green to yellow area on the bar in the calculator, represents the nominal value for setting your bias. Note: If you don't have Microsoft Excel and you can't run this calculator. An average bias value that will work good for either tube in most cases is -35ma. The calculator just enables you to adjust it more precisely based on your specific plate voltages.

6.  Now go back to your powered down amp, set your Digital Volt Meter for -ma (milliamps). This will probably require you to move the probe leads on the meter to different plugins as well. Then put your positive lead on pin #3 of one of the power tubes and put the negative lead on the red center tap wire from your Output transformer. The center tap can be most easily attached to from the small wire connecting  the red center tap and a black lead on the lower left corner of the circuit card as seen on the Layout Diagram. Now power up the amp in standby mode with all the pots still turned down to '0' and adjust your bias pot to the value you got earlier from the Plate Load Calculator. Power down the amp, move the positive lead over to the other power tube's pin #3, power back up, and verify that the reading is the same. Note: if the readings don't match, the most likely cause is that you're not using "matched power tubes". But if you've verified that your tubes "are" matched from a reliable source, then your problem is most likely related to component drift and/or a component/wiring mistake.

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If everything went as described in all the earlier steps, you now have your amp adjusted to the correct bias voltage, and you're not getting any strange noises, try plugging in a speaker if you're not already using one for the dummy load. Then verify the following:

	Power up the amp with a speaker plugged in but no guitar plugged in yet. Turn the standby switch 'OFF' and see if it's still quiet.
	Start to dial up all the control pots slowly and see if the amp continues to stay stable until you get them all up to '10'. At this point you should hear some low volume hiss or hum, this is normal. Any LOUD noises, squealing, or motor boat sounds are NOT normal.
	Now if that all worked, put the amp in standby, plug in your guitar, switch the standby back 'OFF', and give your amp a whirl to see how it sounds. If everything sounds good, you're now ready to drop it into your cabinet.

Note: If you're getting any strange noises, don't despair. I didn't get mine up the very first time either. This just means you'll need to check out the troubleshooting FAQ here and possibly ask a few questions over on "The Crossroads". Most times, you'll find that the problem is a simple wiring or component value mistake.

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Now that you've got your amp working properly, it's time to drop it into it's new home. If you're doing a "bare bones budget" or "player" version, you simply need to put the chassis back into the head cabinet. If you've purchased a new Vibroverb cabinet, then you'll want to drop it in there. See the following tips before you start.

	Speaker Orientation If you're using a JBL, the speaker wire connectors will typically be set at about the 5 o'clock orientation mark. (Other speakers may vary) Put the speaker on the mounting screws, but don't bolt it in yet. Then slide in the chassis to make sure the output transformer clears the speaker frame. If not, rotate the speaker as necessary to accomplish this. Then bolt it all up. If you used a larger than normal output transformer for the SRV Vibro-Clone, then hopefully you remembered to either order the cabinet with an offset speaker hole or a non-standard mounting screw orientation to accommodate your speaker.
	Faceplate If you're using the original faceplate that came with your particular chassis, you can skip this step. If you're using a hybrid "Vibro-Clone" or reissue Super Reverb plate to accommodate keeping the mid control, then remove the old plate carefully. If you're using an original Vibroverb faceplate, make sure you've remembered to remove the mid control and shift all your adjacent pots down one hole. The last hole will be covered by the faceplate now. Note: Remember that in addition to removing all the switch screws, knobs, pot nuts, and the pilot lamp, you also need to remove the inner sleeve of the pilot lamp which is held on by a nut inside the chassis. Failure to do so will result in damage to your old faceplate and an inability to install the new one. Note: If you're using a reissue Super Reverb faceplate, you'll need to slightly enlarge the pot holes to accommodate the silverface era sized pots.
	New Cabinet Chassis Holes If you've already tried bolting up your chassis before reading this, about now you're probably noticing that the rear holes in the chassis don't match up. This is because the head mounted chassis like the Bandmaster Reverb use a more narrow chassis strap. Simply take your new chassis strap, line it up with the hole nearest the faceplate, mark the location of the rear hole, and carefully drill a new one with a 11/64 drill bit. (MAKE SURE YOU DON'T HIT ANY INTERNAL WIRING OR COMPONENTS). Now you're ready to bolt it up!
	Reverb tank leads Make sure you install your reverb tank so that the leads dress up the right side (as looking into the amp from the back). Otherwise, you'll induce an excessive amount of interference hum into the reverb circuit from the power transformer.

Now just slap on the back panels and you're ready to jam!

 

Here's "My" Baby

 

    

A "few" of the details...

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