Blackface Bassmans/Bandmasters

[Brad Bosenberg]

Hi everyone

Can someone tell me the differances btw the AA864, AA165, AB165 Bassman circuts;

and how the AB763 Bandmaster differs other than being 40w. Thanks

Brad

[jay42]

Can't say much about the Bassmans, except that one of the AA versions is considered the best. The Bandmaster has a tremolo circuit and has a smaller output transformer than the Bassman or a Super Reverb. Then again, some like them stock.

In looking at the 65 schematic, it looks like they were trying to lower the gain a bit. The Bassman's gain staging is more like the reverb amps than the non-reverb versions like the Deluxe and Bandmaster. There's an extra triode in between tonestack recovery and the phase inverter.

[Blue Strat]

Hi everyone

Can someone tell me the differances btw the AA864, AA165, AB165 Bassman circuts;

and how the AB763 Bandmaster differs other than being 40w. Thanks

Brad

What sort of detail are you looking for? I could give you the detailed circuit by circuit, component by component run down, but it wouldn't be useful if you can't read schematics. If you CAN read schematics you probably wouldn't be asking this.

So, what exactly are you after?

[Brad Bosenberg]

Hi Mike

I had heard that one of the AA Bassmans was better. What is meant by better, sonically?

Where was the bandmaster designed to slot in sound wise? It was obviously designed for guitar instead of bass, and it has trem. Is that why the tranny is smaller?
If the bandmaster has 40w it would overdrive sooner, eh.

I guess I want to know what the differences would be if I plugged my guitar into either one. distortion characteristics, cleans, highs, lows, etc. thanks

[Blue Strat]

Hi Mike

I had heard that one of the AA Bassmans was better. What is meant by better, sonically?

Where was the bandmaster designed to slot in sound wise? It was obviously designed for guitar instead of bass, and it has trem. Is that why the tranny is smaller?
If the bandmaster has 40w it would overdrive sooner, eh.

I guess I want to know what the differences would be if I plugged my guitar into either one. distortion characteristics, cleans, highs, lows, etc. thanks

Since there is no "better", it's hard to say what "better" means. It's all subjective and what's better to one player sucks for another player.

In general, the 864 is preferred over the AA165 and the AA is preferred over the AB. You'll always find someone who disagrees though. Also note that you could listen to 10 864s and they'd all sound different. Same for all the other models. 40 years later, components have drifted which makes each amp unique.

Yes, the Bandmaster produces less clean power (especially low end) due to the smaller output transformer.

All of these are great amps in their own right. You need to listen to them all, and several of each to make an informed decision.

[phsyconoodler]

For guitar the AA864 is head and shoulders better than the AB165.The later being better for bass guitar.
The phase inverter on the AB165 is very funky and sounds dull and lifeless with guitar.The AA864 is probably the best sounding head of that era.It is loud but has nice breakup and lots of harmonic overtones.The bandmaster is alright for guitar too.The OT is smaller but it is not a whole lot growlier than the bassman.
don't be tempted to buy an AA or AB165 unless you are handy with a soldering iron.You will immediately want to change it to an AA864.

[Blue Strat]

don't be tempted to buy an AA or AB165 unless you are handy with a soldering iron.You will immediately want to change it to an AA864.

Except that he doesn't know what an 864 sounds like ;)

[Brad Bosenberg]

I was looking at something to play roots-rock stuff. I have never played an old fender head -but I always thought they were cool with the piggyback setup.
Vol is not a problem so it would be cranked a little, with some help from a rangemaster or Barber LTD. That AA 864 sounds nice

I will be playing a Hamer with seth lovers and need something that is punchy and tight clean, with some growl as you turn it up.

Mike, ever hear of folks running either of these heads with KT66s? thanks for all the replies

[ChickenLover]

The AB763 circuit in the Bandmaster is the typical BF Fender circuit that's pretty much the same across almost all the BF guitar amps...the Deluxe/Reverb, Vibrolux/Reverb, VibroVerb, Pro Reverb, Super Reverb, Twin Reverb, etc. They all have basically the same circuit aside from power tube/OT/PT differences (and slight circuit adjustments for them) and then if they have reverb that's another addition. The Bandmaster is a bit dirtier than many/most of the amps above.

However the Bassman circuits are different from the above and even the AA864 and the Ax165 circuits are quite different from each other. IMO they all can sound pretty good. The AB165 can actually do the roots-rock stuff pretty well. An AA864 Bassman will likely cost a lot more than an AB165 and an AB165 can be modded to be like an AA864 fairly easily if the person knows their way around tube amps.

[Blue Strat]

Mike, ever hear of folks running either of these heads with KT66s? thanks for all the replies

A lot of people have wanted to, but KT66s are too tall to fit in the head cabinet.

You can get roots rock tones out of ANY of these amps keeping in mind that specimens with the same model numbers sound different from one another.

[Brad Bosenberg]

thanks everyone :BEER

[mageerc]

I have a '66 Bandmaster that is an AB763 circuit that I though was a bit anemic even after having it serviced with new electrolytics and such. I purchased a new OT from David Allen, a TO40MT, and the difference was like day and night. Extremely tight bottom and just much more dynamic in general. The Bandmaster was a good amp, but just a bit crippled with the output transformer that was used...

[Wakarusa]

The whopping difference in the AB165 circuit when compared to other Fender designs of the period is the use of negative feedback.

The first place to look is in the "third" or mixing gain stage right before the phase inverter. In an AA864 the bass channel has three gain stages, the normal channel two gain stages (in a very similar configuration to an AB763 circuit) with the two channels coming together through mixing resistors into the phase inverter. In the AB165 this "third" gain stage is shared by both channels and has a local negative feedback loop on it (partly made up of the 470K resistor going from plate back to grid on the schematic).

Next in the AB165, there is again local negative feedback in the power amp. It's the 220K resistor from 6L6 plate back to the PI plate (and coupled through a cap back to the 6L6 grid). And, finally, there's the "usual" global negative feedback from OT secondary back to the PI input.

All of this NFB comes together to make an AB165 sound tighter (and, in my opinion, a lot less sparkly) and have very different dynamic range than your average Fender of the period. Too, when the AB165 finally breaks over into distortion the transition tends to be much more abrupt and have a more "metal" (read: harsh to my ears) character than its relatives.

[pfflam]

Jeezuz . . . I just bought an AB165 and I thought it sounded unbelievably fantastic.

Guess I was wrong ;)

[devbro]

Good question Brad and you're still welcome around here even if you don't know how to read schematics :rolleyes:. By actually knowing the answer, Todd nailed your question.

[phsyconoodler]

All I can say is if you thought the AB165 sounds great,you are in for a real treat when you play the AA864.
The phse inverter is the real key here.The negative feedback too.

I have KT66's in mine and they fit fine.The bandmaster cabinets are too short for KT66's.

[pfflam]

Can i simply look at the guts of my amp and tell whether it has already been modded?

Would somebody be able tell from a picture?

And how easy would it be for me (a complete hack) to modify?

[devbro]

Short answer - No. You may be able to spot obvious mods but there could be other less obvious changes that only comparrison with the schematic would reveal.
Same problem.
If you're handy with a soldering iron and understand the dangers of working with caps and how to safely discharge them - yes. The problem will be knowing what needs to be changed.Fortunately, there are allot of very smart people on this board that have helped me countless times. If you can take good quality photos and can annotate them with something like Photoshop to help you describe your questions, you can probably pull it off. If I can do it, anyone can. :o

[jay42]

Can i simply look at the guts of my amp and tell whether it has already been modded?

Would somebody be able tell from a picture?Anyone used to working on BF Fenders would be able to tell you in a few minutes time in person. Basically, there's a look to 40 year old solder joints and Fender was consistent with components then. If the amp was repaired somewhere along the line, there may be some components that look wrong, though they may be stock values.

1st test. Does it have the original 2 prong AC cord? If not, it's been modded at least in that respect.

2nd test. Does it have the original power supply capacitors? They're the most likely parts to have been changed.

3rd test. Any blatantly obvious things like extra holes, pull switches, flying components, blobs of goo, ext spkr jack replaced with a pot, switch or a jack.

This is supposed to be a '66.
http://p2p-amps.com/chassis/display.aspx?curpage=34

This one looks like three caps have been replaced
http://p2p-amps.com/chassis/display.aspx?curpage=62

[tlpruitt]

The AB165 can sound pretty darn good in stock form. The normal channel can definitely "grind" due to its use of the third gain stage as mentioned above. Years ago I modded my AB165 "partially" to the AA864 circuit by changing the PI to the more standard type found in the AA864 circuit and by removing the 220K feedback resistors on the power tubes. I left the normal channel's use of the third gain stage in tact. It turned out great.

Another popular option is to convert the bass channel to a 5F6a type circuit. All the basic pieces are there in the 165 and the 864. I did that 15 years ago to another bassman head I have and it turned out great.

-Tim