Which Vibroverb?

[Cliff Schecht]

I think my next Fender build is going to be a Vibroverb. But I'm not sure which circuit would be the best to start with. I'm looking at the AB763 version as the most likely candidate because of the lack of a tapped treble pot and the use of two 12AT7's (as opposed to finding 6 good 7025/12AX7's to shove in a Brown clone).

The brown Vibroverb is quite revered from what I've seen but I also suspect this is as much because of the rarity of these as it is the sound..

So, what circuit should I build? I only see slight tweaks between all three schematics (6G11, AA763, AB763). Are there modifications I should consider or (preferably) build it stock and modify it from there? I will probably make this into a head as opposed to a combo and source a 15" speaker/cab setup separately..

I look forward to discussing this guys!

[NickC]

I used the AB763 for the Deluxe Reverb I built. It's a great circuit. I love the tone. I don't think you can go wrong with AB763. The only mod of substance I did was to add a switch on the back panel to defeat the NFB.

0.02

[crbowman]

Cliff,
The Brown Vibroverb is 6G16. 6G11 is Vibrolux. (Sorry, don't mean to be nitpicky).
I have an AB763 DR as well, and you really can't go wrong with that circuit.
I have little to no experience with the brown Vibes, but I've always heard (take this for what it's worth) that they sound wonderful with somewhat better vibrato seeing as there is no optocoupler.
If you want a slam-dunk, do the AB763.
If you wanna roll the dice go Brown.

[topbrent]

You could build the hoffman style ab763, it uses the 6g16 bias trem.

[ER]

I had the brown re-issue as my main amp the last 12 years and just sold it not too long ago. Great amp. I love the brown tremolo and the 2-10's over the 1-15" black face, but if you're building a head that's less important.

If you're looking for the SRV thing you have to change things up a bit, there's some good stuff in tone quest report about his Vibroverbs, and some interviews with his amp tech to find out the skinny on the mods. Personally I'd go stock unless you play e-flat 64's and need the amp to go louder (you won't need louder).

The deal with the vibroverbs seems to be not having the mid-pot, and the 40 watt power section, playing live they just hit the sweet spot tone and volume wise.

The tapped pots are available. I would build a single channel brown face and add a bright switch. Either way you gotta try the brown tremelo.

-ER

[David Root]

I second the brown tremelo. I have a '62 Deluxe, which only uses one triode and it's awesome.

The brown Vibroverb uses two triodes, so it should be even better.

[Cliff Schecht]

TBH I didn't even see the optocoupler the first time I looked at the A*763 schematics. Do not want. I know the tapped pots are available so I'll probably just go that route and build a brown amp (6G16, not 6G11 ).

From what I've seen online these had pretty wimpy OT's so I'll probably put something more beefy there (looking at Mag Comp and Edcor). Like I've said before I don't like the sound of undersized output transformers, they lack bass AND treble response and make the amps too "honky" in the mids, for a lack of a better term. Good for some but not what I'm after.

What about subbing out the two 12AX7's (reverb driver and possibly PI) for 12AT7's like in the later schematics? Or at least the reverb driver, the PI has different values between the blackface and brown era designs..

[azatplayer]

Ah Cliff, timely discussion. Ive just been talking up doing a vibroverb myself lately. Interested in what you choose and what iron u use. Ive got a stack of iron i need to use up.

[Cliff Schecht]

As far as what I'm building, I'm pretty much set on building a brown amp first. I've played my fair share of blackface amps but not so many brown amps and am yet to build one from that era.

I'm not sure on the iron yet. I've got a few ideas lined up but am most interestd this guy: http://store.triodestore.com/surebareupho.html. The relative size and M6 laminates should make for a great fidelity transformer, something I prefer in my builds.

As far as a power transformer, I just bought a few 800V CT transformers from Dynaman. They're all beefy and it's easy to handle the little bit of extra B+ with a HV CT zener circuit (be it a high wattage zener or a power transistor based zener amplifier). I find these circuits have no adverse effect on the sound or feel of an amp other than changes that would occur naturally if you moved around the B+.

FWIW the only reason to hassle with all of this is because for the few dollars that these fancy zener circuits cost, you can use transformers that are much cheaper than anything new. I'm yet to have old US-made iron fail on me (good to test these before using them though!) and usually pay anywhere from $15-25 shipped. The downside is you need to run the amps on 117V, but that's not a big deal. A line voltage bucking transformer or a variac works wonders here.

The massive transformer I used on my tweed Twin build weighed 12 pounds and cost me $20 shipped on fleabay. I'm a student still so I have to keep this hobby affordable .

[billyz]

I have owned and played both vibroverbs, original ones not reissues. The Brown Vibroverb is my favorite. It is a very different amp and special. The blackface vibroverb is basically like all blackface amps with a 15" speaker. the reissues do not sound anywhere near as good as the originals either, so don't judge them by that .

[renshen1957]

From what I've seen online these had pretty wimpy OT's so I'll probably put something more beefy there (looking at Mag Comp and Edcor). Like I've said before I don't like the sound of undersized output transformers, they lack bass AND treble response and make the amps too "honky" in the mids, for a lack of a better term. Good for some but not what I'm after.

What about subbing out the two 12AX7's (reverb driver and possibly PI) for 12AT7's like in the later schematics? Or at least the reverb driver, the PI has different values between the blackface and brown era designs..

Hi Cliff,

Although they got "pricey" with the decline of the dollar and the recent price increases, the Hammond 1650-N is a beefier, full range transformer about with a primary at 4300 ohms.

No reason you couldn't substitute the 12at7 (or for that matter 12az7) or even a 12au7, the heater currents are the same, the tone will be different because of several factors.

The super reverb, ect transformer is 4200, ect, also used in the Super 60 210 (OEM Magnetic Components), is the same watts but a little smaller, but the price is about half of the hammond. (Also paper wound, not plastic if you are into that sort of thing.)

Best Regards,

Steve

[ER]

I agree the originals sound better but the reissue still sounded great and was more versatile, not as loose with the SS power supply. I played a brown super that was a serious blues machine.

Mine was a special one, I wanted a 2x10 combo after I sold off my big 'ol rack rig and went to a guys place where he had the VV reissue, and a K&M prototype with 2-10" jensens and built out of a black face bandmaster reverb. I played those suckers for 4 hours because the guy said I could have either one for $700 bucks. Let me tell you it would have been nice to have $1400 bucks at the time, finally I dimed 'em and got the tremelo going and I left with the '63 reissue and can't really feel bad about it since I could only have one amp at the time.

I would just use the reissue iron, there's something to be said about the 40 watts vs. 50 watts, and you'll have no shortage of low end if you do the solid state power supply and 2-10's. I love edcor iron, but don't feel like you have to go oversize or higher voltages, you might not get the tone.

-E

[bigsmitty]

If you go to prowess amps. com you can find schematic for fender custom shop vibrverb with the diaz mods

[renshen1957]

If you go to prowess amps. com you can find schematic for fender custom shop vibrverb with the diaz mods

A Google of the Diaz mods will bring up a discussion of SRV's vibroverb having its output transformer replaced with a Fender Twin transformer connected to an 8ohm 15 inch speaker (a JBL or equivalent) on the secondary. Transformers built to the twin ratios which in this case would yield 4,000 primary (with an 8 ohm secondary) instead of the twins 2,000 "primary" (with a 4 ohm speaker).

Discussion is at http://www.thegearpage.net/board/archiv ... 25793.html

This would be 4,000 ohms (the same as the anemic stock vibroverb transformers) in bigger transformer. A twin transformer by magentic components would be less dollars, and hand wound in the USA, than the Hammond 1650N (which as memory serves me about the same size, Fender has a history of using undersized transformers).

A toroid OT would be bigger sounding still, but maybe too Hi-Fi sound too clear. http://www.antekinc.com/pdf/AT-040L.pdf, but this is currently out of stock.

[godi]

Hello Cliff

I made a Vibroverb clone starting with a Bandmaster reverb amp (head) I bought a silver face 1974 as a base pretty cheap (something like $450) then I converted the circuit to a AB763 specs with a 15 inches Weber California speaker, you can go wrong, this made a fantastic sounding amp.

[img:800:910]http://www.jeangodbout.com/vibroverb/IMG_4509-800.jpg[/img]

The output transformer have been change for a Allen (Heyboer) TO40MT with great results. A week ago I ordered some cotton wires from Hoffman Amps and I'm planning to rewire the complete amp to look more to a black face than a silver face, I know it wont sound better, but the wiring on a 1974 silver face is not very nice, so that just a luxury to please me.

Doing this, I will also change the caps with my homemade blue molded caps repro I made with paper and oil Russian caps, they look like this :
[img:610:354]http://www.jeangodbout.com/princeton/fa ... ed-cap.jpg[/img]
I used air drying clay to make the cap end (halft ball), blue paint and a fake sticker.

You can see more details at : http://www.jeangodbout.com/vibroverb/clone-1-en.html

Cheers, Jean