Fender Bassman AC568 To AB165 / AA864 Hybrid Pt2

Be sure to check out part 1 before watching this one.
In for a full restoration and mains conversion.
We also decided to make this one sound as good as we can, originality be damned.
The AC568 circuit is regarded as one of the worst sounding Bassman circuits from the era.
We get the best parts of some more desirable designs and graft them together.
What we end up with is a pretty versatile amp.

[@Jim_Cox]

I have to watch you and Lyle's videos several times before things sink in, sometimes picking up on things I didn't catch the first two times. Haha. I just now figured out how the '100 ohm resistors change' for the grid heater power works. I mean both of you explained how it worked but I just figured out which center tap wire to blunt cut and isolate rather than having it go to ground. I had to look at some Hammond 290EX diagrams to help. The Fender AB165 diagrams show both windings of the main PT but don't have any detail. The layout drawings have wire colors but the diagrams just have the wires shown with no detail. Between the two of you, Uncle Doug, D-Lab, Robinette, various diagrams across the internet, I might just learn a thing or two. I just hope I know 'enough' before I tear into this '67 Bassman I just bought. lol

[@BradsGuitarGarage]

Feel free to reach out to us with an email if you get stuck, mate! You're one of the good 'ol O-G subs!

[@markg1051]

Great job and playing Mr W. Thanks

[@BradsGuitarGarage]

Thanks for watching, mate!

[@weschilton]

Yeah man, that overdrive in the first channel sounded great!

[@goodun2974]

One helpful tweak for reducing noise that you might have actually done but didn't mention here is checking the twisted pair heater wiring to the preamp tubes with an ohmmeter, and flipping connections at individual sockets as needed to ensure that they are all phased the same. This is much easier to do if the 2 wires in the twisted pairs are different color, and a pain in the neck to do when the wires are identical, but it really pays off in lowering hum and noise.

[@tedmich]

Do you mean twisted pair heater wires in phase ? I'm confused.

[@goodun2974]

@@tedmich , for the preamp tubes, all pin 9 heater connections should be fed with the same wire, and pins 4 & 5 ( they're tied together) fed from the other wire of the twisted pair. Because the 12A-7 family of tubes has two series wired heaters per tube, with a center tap, they act a bit like humbucking pickups, especially if the heaters of all the tubes are phased the same.(The same general thing applies, but to a lesser extent, to the heaters of the output tubes: pin 2 to pin 2 and pin 7 to pin 7, for 6L6, 6V6 and their kin). Amp builders and some amp companies companies will use dissimilarly- colored wires for the heater circuits in order to make in-phase wiring easier to do; but you can still do it with heater strings where both halves of the twisted pair are the same color, it's just a little bit harder to do. To improve hum levels in an existing amplifier with all the heater wiring being the same color, disconnect one side of the heater's secondary supply where it is fed from the transformer, and then use an ohmmeter to figure out which pins are connected to each leg of the heater-supply line; unsolder, remove and flip the wiring at individual sockets.

[@PsionicAudio]

Golf clap

[@tedmich]

Bravo, nice rebuild! that little Deltalite cab you made sounds GREAT on the bass with this amp! Are there plans for this cab somewhere?

[@BradsGuitarGarage]

There are plans for that cab and others on my computer, yes. Being the one that designed it. We're doing another run of 1x12" and 2x12" guitar and bass cabs soon, I wasn't really doing many videos when I built the last run of them.

[@tedmich]

@@BradsGuitarGarage I wish you well in your continued efforts ! As a Amp Tech and Cabinet maker you are uniquely qualified to make some nice rationally designed cabs ideally incorporating the work of Thiele and Small ,which as it turns out is strongly linked to Australia! Modern guys would love an honest 60Hz response I reckon!

[@BradsGuitarGarage]

Playing a downtuned guitar with distortion through this cab is a bit of an enlightening experience and hard to come back from.

[@Shiloh7377]

While your playing/trying the amp out, lm jamming a cool A thing along with ya.....🤘🤘

[@BradsGuitarGarage]

This is the song. We're born with this band in the blood in Australia: kzbin.info/www/bejne/h3uyXoycetmXhKM

[@JEmilioJNava]

Which model are you using as "fly back" diodes?

[@BradsGuitarGarage]

Reticon R3000F

[@JEmilioJNava]

@@BradsGuitarGarage thanks! ... *Rectron R3000F

[@georgebush8038]

now it looks like an amp, does sound like a good guitar amp than a bass amp

[@BradsGuitarGarage]

Yes, it pales in comparison with modern amps when it comes to power, but it'd be a great bass recording amp in the studio. Just a hair of overdrive on a P-bass in you're in heaven.

[@russellesimonetta3835]

Uhhh that polarity switch,,,, how about a mid pot?? I think fenders need mid pots. The higher tier amps had mid pots.

[@BradsGuitarGarage]

That's not a bad idea, but the position doesn't lend itself to nice wiring layout. The owner was happy to just leave it unused, being at the rear, too.

[@goodun2974]

@@BradsGuitarGarage , most people never use the Normal channel in a Fender amp; it seems to me that we could/should take advantage of that rather marginal channel in creative ways.

[@BradsGuitarGarage]

In this case, guitarists are more likely to use the normal channel, but I understand what you mean.

[@kbkman7742]

I stuck a master volume in that spot on my ab165. Perfect position for a rudimentary cross line master

[@Splattle101]

I set the ground switch on my old Super Reverb to switch the negative feedback on or off. It was a very easy non-invasive / non-destructive change. REALLY changes the sound.