Bassman AA864

[C Moore]

In the Bass Channel tone stack, at the 250pf cap - 220k resistor. Is that a high pass filter? If I were to remove the 220k, would more high frequency pass, controlled by the 250pf?
Or more simply put, what happens when that 220k is removed?
Thank You
http://www.el34world.com/charts/Schemat ... _AA864.pdf

[BTF]

That circuit approximates what you'd get with a normal treble setup turned down quite a bit. So yes, it's a treble attenuator. If you remove it, the treble pot may need to be replaced as it will probably seem quite ineffective. I have that amp, and the entire channel is set up to create a dark, boomy bass sound. You can plug an electric guitar into that channel and get a big, dark bassy tone. I plugged a P-Bass into that channel once, unplugged it and never tried it again.

Also, the .001uF cap in parallel with the 220K on the third triode is a treble attenuator as well.

Hope this helps.

[Structo]

That would be a very easy amp to mod into a killer clean/overdrive amp.

[M Fowler]

I am in the process of building the amp right now and loaded about half of my board Saturday.

I am going to stick with the stock AA864 values. But man that layout is hard to read so it's a good thing I have a decent PDF of the schematic.

Oh and I am using 715 ODs.

[C Moore]

BTF - Thanks for the info. If I remove that 220k , Would I be going over board with a 500k pot while retaining the 250pf cap. In you opinion of course, not looking for any guarantees from anybody...... I guess what I am trying to do, if possible, is to make the bass channel more guitar friendly without duplicating the normal channel or going too mod crazy.

Structo - I have another Bassman head also. That is the one I will be looking to mod a bit more. It is a real beater, and will never be sold; so no worries about what I do inside.

Hey Mr.F - I would be real interested in your opinion of the "Bass Channel" when used for guitar. Can you get back to us when you are finished with that build.....?

Thank You

[M Fowler]

I have had so many bassman amps in my life time and used them for guitar until I ran across my Tremolux.

Used that Tremolux exclusively, but sold that to Mike Keller and not sure if he ran that when played he with Double Trouble or not. I was suppose to get a 59 Bassman 410 in trade but his dad bowed out on the trade deal.

I'll get back to you on this though. This amp will sound better than an original or I will have to start over.

[BTF]

Over the years (and before I realized that the 864 was going to become such a Big Thing) I used my 864 for experiments. I put it back stock except that I did rework the Bass channel. I simply hate the sound of that channel.

Sure, you can replace the treble pot with a 500K. It will go a bit darker and brighter than the 250K option.

To tell you the truth, I cannot fathom WHY people go crazy for the 864 except for the fact that it was made for only a year or so. During my experiments, I wired it as a 6G6B (with my current bass channel) and I tell you it was God's Own Amp as far as I was concerned! It had a fantastic clean, and a crunch so creamy you were ten pounds heavier after you played it.

Sadly, I'm a nebbish and felt guilty after the 864 became so Holy. That's why I put it back. I still feel the 864 is a POOR second to the 6G6B. Its crunch is grittier and more one-dimensional than the 6G6B. But beauty is in the ear of the beholder, so what do I know?

Good Luck to All! Bill.

[M Fowler]

Yes I like the 6G6 tone stack wiring myself which is very similar to a Komet 60.

If you lower the 250pf that should help with mid range, keeping the 220k as is.

[C Moore]

I took a quick peek at the 6G6 (A or B). There is a huge difference on the bass channel I see. Cat follower to drive most of the tone stack, and the treble pot is handled differently. The 6G6 also uses both halves of that last triode before the PI. So I can read a schematic, but I do not have enough knowledge to know what it all adds up to? I guess the 6G6 would be a Blonde or Brown amp. Does a guitar sound any better through the Bass Channel of a 6G6 than it does through a Black Face circuit? My ears have no experience with a Blonde Bassman.
Thank You

[M Fowler]

http://www.youtube.com/watch?v=LUv4iUWLOAA

Well maybe there's better videos

[BTF]

One thing I'll point out is that I was not using the Bass channel stock or modified to get my sound. When I redid the Bass channel, I completely reworked the channel first using a tonestack setup recommended by Ken Fischer, then I later used essentially the same setup but with a 59 Bassman tonestack driven from the plate. Ken's stack was very smooth, but a bit toppy. The Bassman stack was a wee bit more old school. My Bassman was wired so that I could use the Deep switch to internally activate both channels. I still use that as it's VERY neat and you don't need the patch cable.

Now that the amp is back to 864, it's a better power amp to use with pedals than a crunchmeister.

Regards!

[M Fowler]

http://acruhl.freeshell.org/mga/main/AA ... AB165.html