Fender AA763

Joe E · Post by **Joe E** » 16 Jan 2004 5:37 pm

I noticed most of the black face amps used the AA763 circuits. What make them different?

I only notice a few that used differernt rectifiers.

Is there a difference between a Pro Reverb, Vibrover and a Super Reverb, other than speaker configuration?

Joe E

Donny Hinson · Post by **Donny Hinson** » 16 Jan 2004 6:26 pm

Many of the BF's were AB763, too! Though they have similarities, there's many subtle (and not-so subtle) differences in the amps you mention. Basic power is the same, but the type of rectification, and the type of bias circuitry were the most significant changes. Many other small revisions were also made in their circuitry (phase inverters and preamps), but most players still consider the rectifier changes the most significant.

For example, I've seen at least four (and maybe five) different schematics for the BF Twin Reverb amp (AB763). The S/F models added another five different schematics, as well as three more circuit designations (AA270, AA769, and AC568.) For these amps, most consider the different powers and the addition of a master volume control to be most significant.

Joe E · Post by **Joe E** » 17 Jan 2004 5:42 pm

Ken Fox · Post by **Ken Fox** » 18 Jan 2004 3:08 am

One difference I have noticed in the schematics is the lack of the 1500 ohm resistors at the power tube inputs (snubber resistors).
Pro Reverb, Super Reverb and Vibroverb are basically the same. The output transformer is a might whimpy in size on a Vibroverb and it also lacks a mid range pot (uses a fixed 6.8K resitor instead). The chassis is wider on a Pro Reverb, due tot the 2-12" speaker configuration.
The last of four Vibroverb clones I built used a Twin Reverb output transformer. It made a huge difference in the bottom end on the amp. Prior to that, I used the stock Bandmaster Reverb transformer (4 ohm, small like a Vibroverb). I re-coned the JBLs to 4 ohms. The amps sounded great, but the larger transformer from a Twin made the difference. I think the transformer in a Super is close to same amount of iron as a Twin, maybe that's why they sound so different than a Bandmaster Reverb, etc.

[This message was edited by Ken Fox on 18 January 2004 at 09:26 AM.][This message was edited by Ken Fox on 18 January 2004 at 09:32 AM.]

Greg Derksen · Post by **Greg Derksen** » 19 Jan 2004 7:09 am

Ken that would explain why I like the sound
of Super reverbs and Twins, The smaller
Vibrolux's and Deluxe's are great for guitar but seem to lack something, not just bass,
but just everything, sparkle, etc, Greg

James Quackenbush · Post by **James Quackenbush** » 19 Jan 2004 8:54 am

There is something to be said for more "iron" in the larger transformers...You can push nice mids and highs to a degree with smaller transformers, but you will loose out on a solid bass performance....For a good solid , not mushy bass responce you need POWER and big iron in your transformers...The more powerfull the amp, the larger the transformers...Larger transformers will give you a bigger , more powerfull tone, with a good solid bass....Look at some of your great sounding bass amps, and then look at the size of thier transformers !!
Bigger is better .....Jim