Rusty Bassman

[Smokebreak]

Hey now,

It's been awhile! I moved out to the suburbs a couple years ago, stopped building amps every waking minute of the day, and transitioned into repairs/mods. Turns out you can make a living do that, and I guess I got good at it by troubleshooting all my builds back then
One of my customers brought over a SF Bassman that he told me on the phone he had scored from underneath a pile of junk and said it was a "2" on a 1-10 scale. My first thought when I saw it was "What would make this a "1".
He said he didn't want to spend anymore than $400 on it, my labor included. When I finally got the chassis straps off, the cab basically disintegrated. When I saw the inside, and the extent of the neglect, I let him no there was no way I could get this done for that price, even if he didn't have to get a new cab.
So he told me to keep it!

This will be my rainy day project, and I guess the first amp I've "built" in a few years. I'm really looking forward to it.
As you can see the rust is pretty bad, but I'm guessing the trannies are fine, and I'll be damned if I can't use most of the stuff on the board. The pots don't even turn lol.
I'll of course need to replace most everything else, but my question is about the rust.

I plan on stripping it down to the chassis, and addressing the rust first. To what extent should I try and remove the rust and inhibit further destruction?
What does doing this up correctly entail?

Cheers- Jeremy

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[xtian]

Welcome back!

Wow. If those transformers are in good shape, I'd pull them out and trash everything else. Ever-y-thing.

[Smokebreak]

Thanks Aaron!
Awww part of the fun here for me is to revive this thing in it's chassis, plus, I'm pretty sure there's some mojo left underneath that rust

[TUBEDUDE]

Dumpster bait. Save the iron, toss the rust.

[Stevem]

That looks real close to the way a Bassman looked that I picked up about 5 years ago that spent a whole summer outside or more outside.

I dryed it out for 1 week sitting on two heating pads, put tubes in it and 2 or 3 new filters and the darn thing played fine, to say the least I was shocked!

[dorrisant]

Strip the chassis down to bare and soak it in a diluted vinegar bath... I did this same thing to a BF Twin a few years back. Pretty sure it was one from the Nashville flood. It took about 2 1/2 months of soaking and ocasional scrubbing, but it did stop the rust. Then I sprayed it with a zinc based paint.

I pulled all of the signal caps off of the original board and started over with a new board. The original was conductive, go figure...

[Leo_Gnardo]

Mid 90's an acquaintance from North Carolina called me, said he had a nice BF Bassman head for sale, only $175. Plus shipping of course. When it arrived, it was the rustiest thing I ever saw. Probably spent its life in shore-side damp salty air, playing at shag dance parties for the locals & tourists. I did the usual trouble shooting, installed all fresh electrolytic caps, let it run for weeks. Turned out to be one of the best sounding Bassmen I ever heard! Sold it to a local musician for 6 c-notes, which covered me for parts & labor. He still has it, still working fine 20+ years later. BTW I did nothing to remove the rust, except give it a bit of a scrub, mostly cleaning the tolex.

If you want to de-rust yours, might be an idea to pull everything off the chassis, have it sandblasted, optionally also treated with phosphate to inhibit further rusting, even give it a nice coat of paint. A good auto body shop can handle all of the above. You will have to scrape paint away in a couple of spots to create good ground paths, maybe also mask off the area behind the control panel if you count on making grounds through the pot bodies the way Fender did.

Rusty transformers? There's a couple of thoughts on this. Some claim has been made, it's a bad idea to wire-brush rust off the lamination stacks. All too easy for flecks of steel to bridge the lams & disturb their effect on the magnetic fields. As long as the transformers are perfectly dried out & have no leakage from windings to frame/lams you're good to go. All in all, best left alone. Maybe, only if there are big gobs of rusticles, a light wire-brushing to knock those off might be in order. Otherwise the lazy solution is best. Also - test the power supply choke for leakage too, due to water infiltration. If it's bad, swap in a new one. Cheap enough & it beats fussing over it.

[roberto]

I would suggest citric acid instead of diluted vinegar: it works better with the material of the chassis.
4%w is a good starting point (40 grams every liter of water). Room temperature or up to 50 Celsius.

Few hours and the rust should be gone.

[Phil_S]

I suggest Google for "rust remover" and you'll see discussion of many different products and methods including phosphoric acid based stuff. I think that I'd be inclined to try electrolysis. It's really a very straight forward process. You'll need a car battery charger, washing soda (sodium carbonate), a metal post, a plastic container, water, and a few other things. Youtube for it. Be prepared to lose the paint on the front panel. If that matter, do something less aggressive. Nice "find."

[Stevem]

You don't want to waste time removing the rust, just get a Brush type paint can of Automotive rust Converter as it changes rust into a primer.

[AtomCap]

looks like workable surface rust - if the irons good, gut it bare, have the chassis media blasted, mask off some areas to tie necessary ground, have it powder coated?

[oj]

Hi Jeremy
the rust is not a big problem, just strip the hole chassi and just taket to company that do the same finish that was original (don't know what is call l English)
They take care of the rost (they dip it in saltpeter) and give a original finish.
Good look !

[Smokebreak]

Thanks guys! I was at the grocery store and saw citric acid in bulk, so I got some, and will go that route and see what happens, as I've got some time to kill today.
I just put 11VAC via a lil step down wall wart I have, and the PT is putting out voltage. At 11V the heaters are at .63VAC, the bias supply at 4.8VAC, and the HT at 60VAC. Doing the math it's all good but the HT does seem a lil high, makes 660V across the secondaries unloaded. However it is too late to not get rust off the trannies, as I did that weeks ago. The lead hole on the PT however is completely sealed so hopefully I'll be OK.
I'm gonna strip the chassis and soak it in 4% citric acid solution in a bin.

[drew]

I think that I'd be inclined to try electrolysis. It's really a very straight forward process. You'll need a car battery charger, washing soda (sodium carbonate), a metal post, a plastic container, water, and a few other things. Youtube for it.

The Youtube video-opiod algorithm got me hooked on watching a guy in Australia renovating an old steel trawler. Episode on electrolysis rust removal:
CAUTION MAY BE ADDICTING

[Smokebreak]

Very cool process Drew and Phil. I ended up soaking in citric acid yesterday for a while , and scrubbing a bit, and am doing again now.
I got a rattle can of Rustoleum and plan on hitting it with that. I'm just gonna order a board from somewhere, but even though my mantra has been "just rebuild the amp...just rebuild the amp", my old ways are emerging, and I can't help but think about building another circuit in here. Any ideas? I'd like to at least keep it in the bassman lineage, something for rockabilly. Maybe 6G6?
Even considering the good ol 5F6a. Any Marshall-esque thing I've ever built into a Fender chassis w/ Fender iron always sounds so good. Anyone ever figure out that Overdrive deluxe 6V6 amp? That would be cool too, with 6L6