Today's "score" - 1965 Fender Bassman Barn Find... allegedly.

[Wally]

Ime, that discoloration is due to environmental conditions…probably tars in cigarette smoke. I have seen Fenders with the same chassis metal appear pristine….no brown/copper coloration. Those ‘clean’ amps were those that were kept in cleaner conditions.

 

[Huddy]

Ime, that discoloration is due to environmental conditions…probably tars in cigarette smoke. I have seen Fenders with the same chassis metal appear pristine….no brown/copper coloration. Those ‘clean’ amps were those that were kept in cleaner conditions.

Yes someone in a FB group suggested that it is burnt on vapor from the lacquer inside the transformer when it overheated. It cleans up a bit with lacquer thinner and little effort - though it might clean up the same with warm water as well. But I just went straight for the hard stuff.

 

[Wally]

Yeah, there has obviously been some smoke get loose in there. There are those who would pull everything out in order to clean that chassis. I like the way it looks…as long as all carbon traces are cleaned.
All,of,the AC wiring needs to be done in best and safest manner. A careful restoration of all aspects of the bias circuit, and the output section has to be done. Fingers crossed on the PT and the OT.
The AB165 is a great amp, imho.

 

[Huddy]

Yeah, there has obviously been some smoke get loose in there. There are those who would pull everything out in order to clean that chassis. I like the way it looks…as long as all carbon traces are cleaned.
All,of,the AC wiring needs to be done in best and safest manner. A careful restoration of all aspects of the bias circuit, and the output section has to be done. Fingers crossed on the PT and the OT.
The AB165 is a great amp, imho.

Good gracious… can’t believe it’s almost been 3 months. Got busy with life but finally got on this thing over the weekend. I ended up pulling everything out because the discoloration was a nasty film of a dusty grime. My mild OCD got the best of me.

I thought I had mentioned this but the PT has an open primary. Got a Hammond for it and will include original on sale if I decide to sell it. However after all the work I will have done I’m probably gonna treat this one like a child and keep for forever.

Cleaned the back plate… front panel before pic; cleaned up pretty good - some wear spots from the knobs are still visible but should be covered mostly when back together.

Scrubbed out the chassis with WD40 and 0000 steel wool and then followed behind with isopropyl alcohol to remove all the WD40 and any steel wool shards.

I think this pic might’ve been after the first pass. It looks a fair amount better than this. Not perfect, but much better than when I got it.

Just waiting on B+4 27k dropping resistor that I didn’t have on hand. Hopefully I can get it done before I go out of town on Sunday.

 

[tele_savales]

Red scotch brite will take that tarnish off. It would leave a fine scouring pattern though. There's much finer grades that they dont carry at my local hardware store so I haven't tried them. Might as well go all the down since you pulled everything off the chassis. That's just me though.
https://www.3m.com/3M/en_US/metalworking-us/products/flat-stock/hand-pads/

 

[keithb7]

Now you're on the right track! Build a solid amp that can be played, not oogled over and un-playable.

Of all the amps I have owned, the bassman ranks very high for break up crunch.. Its a rock'n roll amp through and though. Especially with almost any Gibson-esque humbucker equipped guitar.
It's darn loud when it sounds best in my opinion. A real stadium amp. Back in the day, bars and their patrons would allow you to crank up a Bassman amp. Today? I think a large stand up acoustic bass is the ceiling of tolerance. Lol.

I recommend the 3 prong grounded cord. Re-assign the rear ground polarity switch to a switchable negative feedback switch. On/ff is my preference. Helps get some nice break up at lower volume. Alas good drive pedals will help get you tolerable breakup overdrive levels. Not quite as ballsy and full sounding as the natural amp cranked to breakup though.

 

[Huddy]

Now you're on the right track! Build a solid amp that can be played, not oogled over and un-playable.

Of all the amps I have owned, the bassman ranks very high for break up crunch.. Its a rock'n roll amp through and though. Especially with almost any Gibson-esque humbucker equipped guitar.
It's darn loud when it sounds best in my opinion. A real stadium amp. Back in the day, bars and their patrons would allow you to crank up a Bassman amp. Today? I think a large stand up acoustic bass is the ceiling of tolerance. Lol.

I recommend the 3 prong grounded cord. Re-assign the rear ground polarity switch to a switchable negative feedback switch. On/ff is my preference. Helps get some nice break up at lower volume. Alas good drive pedals will help get you tolerable breakup overdrive levels. Not quite as ballsy and full sounding as the natural amp cranked to breakup though.

I haven't worked on it since I posted last. Hope to make time this weekend and get it knocked out. I've been scanning a bunch of forums looking for common circuit mods and there's a big consensus around removing the local negative feedback on the AB165 - not sure how that affects the global negative feedback but... i'm open to guessing and checking. With the replaced PT i'm going to take a couple liberties that I perhaps wouldn't do if it had all it's original iron. I've never played through one of these so I don't know what I don't know. Cross your fingers for me that I can make it happen.

 

[keithb7]

Negative Feedback off:

 

[keithb7]

Another example for you, negative feedback was mad switchable:

 

[Huddy]

Another example for you, negative feedback was mad switchable:

Yeah at first listen I kinda like the AA864 better between those two clips... I'll have to re-listen with some good headphones to verify.

 

[ETMusic777]

Yeah at first listen I kinda like the AA864 better between those two clips... I'll have to re-listen with some good headphones to verify.

I have both... a late 64 AA864 and a 67 BF AB165. Both sound very similar at lower clean volumes, but the AA864 is a touch "sweeter" on lower volumes. At higher volumes through a Fryette Powerstation, the AA864 overdrives like the best blues amp ever made, and the AB165 crunches like the best rock amp ever made. If I were recording music for a Harley Davidson road TV commercial, Id use the AB165 as it rocks out. If I had to choose one over the other though it would probably be the AA864 but its very close.

This guy gets some nice tones out of his AB165



This guy gets a nice tone too

 

[Gunny]

That a project I would love to have. It's too far away for me. I've got the time and skills to restore it (and as a bass player, I'd play it too) but these restorations aren't for everyone. My personal goal would be functional, safe restoration of the amplifier. Once it's up and working right again, Joe Average doesn't know or care about the appearance of what's inside; they ought to be impressed by how awesome it sounds. Some guys want an 800 Watt solid state bass amp. This one would suit my needs just fine.

 

[Huddy]

Finally got on this thing. Coming along nicely.

Hope to get the preamp portion done done tomorrow morning but with my track record - don’t hold your breath.

 

[1 21 gigawatts]

That is looking good. Huge improvement from where it started!

 

[Huddy]

I’m such a bum. Finally got the preamp stuff done. On to the heaters. If these wires have DC on the insulation or are microphonic I’m gonna be super discouraged.

Planning on firing it up tonight without tubes and checking voltages and test with tubes in the AM.

 

[Huddy]

Volumes are super scratchy. Won’t seem to come clean. No DC present. .01 uf ceramic disc after 220k mixing resistors is beyond microphonic.

A couple of the sockets (or the tube pins) need some extra attention. Will do cleaning and some rolling if need be tomorrow.

But it’s alive and making sound. My only cabinet is 16 ohm so I had my only 8 ohm speaker was just laying on the dining room table. Hard to say what it “sounds” like at this point. Need to borrow or buy a cabinet for this type of testing and future use.

 

[zook]

Nice job. I love to see things brought back like this.

 

[Huddy]

Small update - Replaced the Ceramic .01 with a Mallory and it's slightly microphone but lightyears better than the ceramic. Rustling persisted.

I had isolated down to the 220 kΩ channel mixing resistors or just before there. I do not own a scope - here are the steps I've taken to reach that conclusion:

• Removed phase inverter (V4) - noise gone
• Sub Phase Inverter (V4) - Noise Present
• Remove V2 - Noise Gone
• Sub V2 - Noise Present
• Remove/Sub V1, V3 - Noise Present
• Ground Grid Side of .01 µF Coupling Cap after mixing resistors - Noise Gone
• Notice Cap is ultra microphonic, sub Mallory 150 - Noise Present, still microphonic in very center of cap, either legs are quiet.
• Lift mixing resistor side .01 µF cap leg - rustling gone, minimal white noise.
• Noticed single digit mv on various locations on the board 1-2 mv mostly with spikes from 8-10 mv - probably not the cause of the noise.

From there I replaced the 470 kΩ V2 feedback resistor and the 2x 220 kΩ mxing resistors and the noise has subsided significantly but it is still present. But then I plugged in the guitar and it's pretty darn loud even on 2-3 - perhaps that's normal-ish while still leaving room for improvement.

• Will replace the associated plate resistors for the second gain stages of each channel this evening.
• Not sure if maybe there's moisture/contamination underneath the board that's not present on the top side causing conductivity - but it's getting to an eyelet from the bottom side I'd still be able to measure it on the top side of the eyelet so perhaps that's not an issue - just thinking out loud ;-)
• It's also possible that heating the eyelets to replace the parts drove away some of that DC on the board - will try to flush as much out this evening as well.

Let me know your thoughts on things I should be looking out for if you have any.

 

[gabasa]

What an exciting project, great work so far!