AA864 vs AB165 Bassman

[Powerstrokedr]

Here is a comparison of the 1965 Blackface Bassman AA864 that I bought not functioning ( all caps had been robbed out of it and resistors were metal film) vs my All original ( except for filter caps) 1965 AB165 Bassman. The AA864 was brought back to life with carbon comp resistors and mojotone dijon caps. All tubes are the same brand NOS rca 12ax7 in V3, jj 12ax7 in v2 for the ab165 which uses v2 for a second gain stage in the normal channel, aa864 does not, and nos sylvania 12at7 in V4. Mullard RI 6l6gc power Amp tubes. Cab is a 1965 fender bassman 212 loaded on top with a wgs invader 50, bottom is wgs reaper 55. Simple playing, not elaborate and clean to illustrate the difference between the amps with one original and one restored with modern parts.
https://youtu.be/LjAYCupiXAs

 

[jeremy]

Re: AA864 vs AB165 Bassman

so what do you think of the two of em? clips are never as good as hearing and feeling the difference in person

 

[Powerstrokedr]

Re: AA864 vs AB165 Bassman

so what do you think of the two of em? clips are never as good as hearing and feeling the difference in person

The all original AB165 sounds looser on the bottom and seems to have more presence to me, however the presence may be the additional gain stage of that circuit. The AA864 seems tighter and a bit more compressed. I think that is due to the higher efficiency of the modern coupling caps. I wish I had the original caps for the aa864 however, I am glad it still has a very convincing blackface fender tone. It is not often that one of these amps are brought back after being completely destroyed. I am pleased with the restoration, but my favorite of the two is the ab165 circuit. It suits my style more as it is more bluesy and when dimed it has that holy grail overdrive. The aa864 dimed has a very creamy smooth overdrive but sounds compressed, almost like a tube screamer kind of sound without the mid hump.

 

[Powerstrokedr]

Re: AA864 vs AB165 Bassman

Oh, forgot to say bias was set the same as well. Both amps were set to 26mA, as the ab165 only has a balance pot, where the aa864 has a true adjustable bias. The ab165 is fixed at 26mA so I set them both there.

 

[Myaccount876]

Re: AA864 vs AB165 Bassman

The bias current is meaningless without knowing the plate voltage. If you want to compare the amps with an equal bias, you should match the wattage dissipation of the power sections. Power (watts) = current * plate voltage - mind you that the plate voltage and negative input voltage will change a little bit when you are playing and running a full signal, so your wattage calculation will have a small margin of error, but it's small enough that you wouldn't notice it in practice. Also with the amps that have the tubes matching (the AB165 has a hum balance too, right?), you could do a really useful mod by replacing the hum balance control with two 100 ohm resistors on the pilot light filaments to ground, and replace both trim pots with independent fixed bias controls for each output valve. That will let you get the desired dissipation while being able to "match" any two output valves so you won't have any extra hum/a need for matched pairs.

 

[Powerstrokedr]

Re: AA864 vs AB165 Bassman

The bias current is meaningless without knowing the plate voltage. If you want to compare the amps with an equal bias, you should match the wattage dissipation of the power sections. Power (watts) = current * plate voltage - mind you that the plate voltage and negative input voltage will change a little bit when you are playing and running a full signal, so your wattage calculation will have a small margin of error, but it's small enough that you wouldn't notice it in practice. Also with the amps that have the tubes matching (the AB165 has a hum balance too, right?), you could do a really useful mod by replacing the hum balance control with two 100 ohm resistors on the pilot light filaments to ground, and replace both trim pots with independent fixed bias controls for each output valve. That will let you get the desired dissipation while being able to "match" any two output valves so you won't have any extra hum/a need for matched pairs.

I took that into consideration, however with the AB165 being completely original, I do not want to alter it at all. I didn't like replacing the filter caps on it, but they were physically leaking so it was a must. This Amp is museum quality condition, so I'm leaving it alone. Basically I wanted to see if amps that had been raped and various parts thrown in them over time could be put back to original spec with original type parts and still sound convincingly like they should. The 864 sounds pretty close side by side and on its own would probably be solidly convincing. This encourages me to find more of these old picked through amps and bring them back. Undo years of messed up work and mods and make them as close to original as I can.

 

[Myaccount876]

Re: AA864 vs AB165 Bassman

Fair enough. I can understand keeping those models stock - they're two popular Bassman variants and you're maintaining their value. If you had a less-desired Bassman (not saying they're bad amps - just less talked about), then I'd say go nuts and make the amp sound however you'd want it (whether that'd be stock or not) because resale for other Bassmans wouldn't be that much.

 

[jeremy]

Re: AA864 vs AB165 Bassman

how much does a bassman head go for these days?

 

[guitfiddle]

Re: AA864 vs AB165 Bassman

how much does a bassman head go for these days?

$600-$800

 

[jeremy]

Re: AA864 vs AB165 Bassman

ok, i remember seeing them for $400 but that musta been while ago

 

[Myaccount876]

Re: AA864 vs AB165 Bassman

how much does a bassman head go for these days?

Depends which model - some can still be found for very cheap. You won't find any other hand wired amps with chassis mounted components at their price point which already is a big plus in my book. I got my Bassman 70 for $450 (July, 2015), and a Bassman 50 can be had for a very similar price and is nearly identical to the AB165 - the only real differences are the negative feedback loop (the only difference here literally being a capacitor), the power section's bias circuit, and possibly the output transformer (the Bassman 50 isn't one of the ultra-linear amps; the Bassman 70 is, and ultra-linear isn't a bad thing). Apparently users on the internet also think the Bassman 50 and Bassman 70 are similar, with the 70 just being ultra-linear, but there's more differences than that. V2 on the 70 has some extra crap on it, and a master volume circuit that I've been contemplating on completely removing because the master volume circuit on that amp doesn't allow you to fully drive the input of the phase inverter circuit, and I always crank both volumes to ten anyways when I use that amp. Another cheaper ultralinear Bassman is the Bassman 10's of the late 70s - those use the same exact output transformers as the Bassman 70. By the time the AB165 came along, they also started putting a .01 capacitor in parallel with the 100K resistor on the plate of V1A (bass channel), and this is creates a rediculous low-pass filter that makes the channel unusable. Just remove that capacitor, and boom the bass channel opens up and no longer sounds constipated.

 

[jeremy]

Re: AA864 vs AB165 Bassman

i need another big amp like i need to shoot myself in the foot with a 12 gauge but it sounds like a fun amp! even my old dr is too loud to crank up most of the time, cant even remember the last time i turned on the dual showman

 

[Powerstrokedr]

Re: AA864 vs AB165 Bassman

I picked up the '65 AA864 that was completely thrashed for 50 bucks at a garage sale. It was off in the corner. The chassis wasn't even installed and the faceplate that is covered was gone. I completely rebuilt the amp. All original all transformers and choke, but all caps and resistors had to be replaced as most were missing or just wrong. I rebuilt the front panel, and used a repro logo and aged blackface cloth. Looks legit. The all original '65 AB165 I picked up for 695. Well worth it. It sounds like liquid gold. However, when I first picked it up, I tried it out in the garage with an extension cord. I was barefoot when I fired it up. I was quickly reminded why power cords get changed to 3 prong and death caps removed. That funny tingling creeper up my left arm holding my LP. I quickly unplugged and plugged it back in the gfi outlet after flipping the ground switch. Talk about a blast from the past. These bassmans can be found cheap just have to look. The cheap ones aren't pretty and require work, but the juice is worth the squeeze.