Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Lizard King on November 03, 2012, 03:44:10 pm
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Just picked up a bassman....mostly because it had the matching 2x15 cabinet. Opened it up and found it is an AA865 which seems to be a POS according to what I've read.
I've seen recommendations to leave pre-amp alone and mod power section to 864 specs. Any other suggestions?
I found a schematic but can't find a layout for this model...anyone have a layout?
Thanks.
{EDIT: fixed title -PRR}
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I can't find any info on a Bassman AA865. Are you sure about the model number?
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D'OH....AA568. Dyslexic
(Have you heard about the dyslexic, agnostic, insomniac? He stays up all night worrying there really might be a dog.)
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Well, here are schematics and layouts for the AC568 (http://www.el34world.com/charts/Schematics/files/fender/BASSMAN_AC568.pdf) and AA864 (http://www.el34world.com/charts/Schematics/files/fender/BASSMAN_AA864.pdf) Bassman amps.
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You probably wont find a layout. But you got the real thing. Just take some good pics. However, there is a layout for the 864 so just rip out everything between the PI and the grids of the 6L6s and then put it back IAW the 864 layout. Just be careful and don't rip out the foundation or a supporting wall. :wink:
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aC568....I'm a two time looser....the first clue were the 150 ohm resistors on the cathodes. It look like a previous owner completely rewired it - no cloth push back wire left, sheilded leads for inputs, and Mallory coupling caps. I wanted a layout just to make sure it was the 568 be not bastardized.....I can use the schematic, it just takes me longer....never know about hidden jumpers under the board....whoever did it did a good job....I'll post some pics if I can figure out how...
Is the stock preamp/864 poweramp the recommended mod?
Thanks
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The normal channel is the same as an AB763, but the bass channel is, umm, voiced for bass guitar. The good news is there are 3 triodes involved and that makes it easy to do something Marshally.
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Anyone ever done the Steve Aloha (sp?) blue guitar.org hot rod bassman mod?
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It look like a previous owner completely rewired it - no cloth push back wire left, sheilded leads for inputs, and Mallory coupling caps.
The shielded inputs are probably new, but everything else you describe sounds stock. Original wire was thick PVC insulation, and there were a bunch of white Mallory electrolytics in that amp. Coupling caps would have been blue with white lettering, don't remember any specific brand (but could have been Mallory).
If they're M150's, then that's new stuff.
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I must be used to older bassman. I'm used to green cloth heater wire and cloth wire everywhere else. The wire used looks to be different gauges...guess I'll be ordering some wire (and maybe parts for a tube recti).
The other caps look standard - the big red ons - but I'm used to the blue tube caps from other Bassmans I've owned-didn't know Fender used Mallorys.
It has both 1/2watt and larger (1 watt?) carbon resistors.
It looks like the under board wires I'm used to have been run on top of the board, which is a good thing.
But what I haven't figured out yet is a brown wire soldered onto the end of one of the input jacks - not an eyelet, soldered right to the outside of the part the pointy end of the plug hits. Internally jumping input channels???? I didn't have time to look to see where the wire went as it goes down through a hole to the other side of the amp. I just had time for a quick look Friday before I had to leave for the weekend.
I'll keep you posted.
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Here is an article with some ideas about bassman amps:
www.tone-lizard.com/Bassman_Modifications.htm#Bassman_Modifications (http://www.tone-lizard.com/Bassman_Modifications.htm#Bassman_Modifications)
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soldered right to the outside of the part the pointy end of the plug hits.
Yikes! I'd like to see a pic of that.
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My bad....brown wire goes from input jacks AROUND rubber grommet (not through) and goes into cap case. It has been cut on both ends so it connects nothing....curious as to what someone was thinking though...
I was thinking more of a complete gut/reconstruct like the hot rod SF bassman found on this site:
www.blueguitar.org (http://www.blueguitar.org). hrt_smbf.pdf
This is my third bassman. Both of the others were AB165. I've read most of the tone lizard stuff when I was modding my previous amps. This one looks like a major build though. There can't be much collectors value in the amp in its current condition.
I finally got rid of the last of my vintage amps - a BF Baseman & drip edge Bandmaster when I picked up a new Super Sonic....thought my modding days were behind me but then this showed up at the guitar store and I couldn't resist....it's like a drug.
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I am curious to know the manufacture date of your AA865 for future reference? Is this amp past the time of Shumacher trannys?
Thx, Jack D
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I am curious to know the manufacture date of your AA865 for future reference? Is this amp past the time of Schumacher trannys?
Thx, Jack D
The transformers date to 1969.