Chassis Corrosion - Dynaco SCA-35

[albusark]

Hi all,
I've become a Dynaco fanatic and have started buying and rebuilding various amps to gift to friends and family. I just received one off the bay and electronically it looks pretty good, was previously recapped and resistored. However, at some point prior to being sold off, someone got it wet and it now has a rust spot on the back and dots of corrosion on the interior chassis. What would you do to treat this so it doesn't get worse, or is it possible to even repair? I don't especially want to disassemble the entire amp to paint the chassis although I probably will if there isn't another option. From my very light research I read that these SCA-35 chassis were painted, and then some say that they are cadmium coated. Any info on this?

 

[century tek]

I wouldn't worry about it but its possible it lived it's life somewhere where the humidity was high.

You can sand the chassis and just paint it with Rust-oleum.

 

[stanko]

I've never seen one painted.

 

[trainbuftony]

They're plated with something.
My sca 35 had hideous corrosion, I painted the chassis before giving up on the selector switch and turning it into a ST35 instead.
Welcome to AudioKarma!

 

[kappclark]

Ditto on corrosion challenges - here is initial condition of my Fisher 400 .. (a donation from a neighbor) .. glad I have the wood cabinet ! Rust or not, the sound is great !

 

[Bicyclist]

I rubbed mine down with WD-40 just to stop the corrosion. In my view it's ok for them to not look perfect.

 

[crispycircuit]

Yours looks good compared to what I work on.. I'd check with gun collectors to see what rust inhibitor they use. Most the time we wipe them down and call it a day.

 

[Jalousie]

The chassis on my restored ST-35 looks about exactly like the OP's picture. Agree with just clean it up with iKlear wipes or something. A bit of corrosion = character on these old SCA-35 and ST-35 units. Dynaco had a budget for these and stainless or chrome or nickel plated was out of the question.

 

[Lavane]

I would just wipe off what you can and call it good. It doesn't look that bad.

 

[familyguy]

Given the age of the amp that amount of corrosion is minor and to be expected for an amp of that vintage.

Here's some before and after pics of a guitar amp I recently did - your SCA is a longway from needing a chassis restore.

 

[albusark]

Holy Guacamole! Ok I feel better, and a bit ridiculous now. Thanks all. I cleaned the chassis thoroughly with wd-40 and called it a day.

 

[albusark]

Given the age of the amp that amount of corrosion is minor and to be expected for an amp of that vintage.

Here's some before and after pics of a guitar amp I recently did - your SCA is a longway from needing a chassis restore.

That's insane. I feel ridiculous now in comparison. You did an awesome job restoring, rustoleum to the rescue. Thanks for sharing.

 

[albusark]

View attachment 3198885

Ditto on corrosion challenges - here is initial condition of my Fisher 400 .. (a donation from a neighbor) .. glad I have the wood cabinet ! Rust or not, the sound is great !

Holy cow that's extraordinary that the amp still works.

 

[albusark]

I rubbed mine down with WD-40 just to stop the corrosion. In my view it's ok for them to not look perfect.

Followed your advice, thank you.

 

[albusark]

The device is clean finally, 35 q-tips later. The bass knob is still being a butthead despite copious amounts of deoxit and contact cleaner and I expect it may perform poorly. The larger can cap is leaking very slightly from the base so I will replace both as they've done their duty and deserve a retirement. By the way, the "M A" 50+50 uF 500v cap is a serious upgrade for these SCA's, you can immediately notice the bass response improvement and for $10 with mounting bracket on parts express, there's no excuse. They test perfectly on ESR meter. Will be checking component values and re-soldering any old looking points, and then will begin testing the amp on oscilloscope. That's all for today, make sure to like and subscribe for more Dynaco content.

 

[Mr Boochie]

Hi all,
I've become a Dynaco fanatic and have started buying and rebuilding various amps to gift to friends and family. I just received one off the bay and electronically it looks pretty good, was previously recapped and resistored. However, at some point prior to being sold off, someone got it wet and it now has a rust spot on the back and dots of corrosion on the interior chassis. What would you do to treat this so it doesn't get worse, or is it possible to even repair? I don't especially want to disassemble the entire amp to paint the chassis although I probably will if there isn't another option. From my very light research I read that these SCA-35 chassis were painted, and then some say that they are cadmium coated. Any info on this?

I've bought several vintage amps with those tiny brown-black dots. From the amp's history, they may be cigarette smoke tar droplets. They are very hard to remove. Rubbing alcohol and Simple Green works a little, but I end up leaving the dots alone.

My Silverface 1968 Fender Bassman. Spent its life working in a bar.

 

[quadtech]

Now this is corrosion -

diytube.com • View topic - Rustiest ST70 Chassis of All-Time??

 

[gadget73]

want to know the easiest way to fix this? Put the lid on and turn the volume up.

 

[albusark]

Nothing beats the logic of things could be much worse. Thanks all.

 

[albusark]

Well it bothered me enough and I was confident enough in a fix that I delved into chemistry and found that oxalic acid in a 10% solution was able to remove oxidation and make the chassis look brand new (using a fine paint brush on the spots). You old dogs can still stand to learn some new tricks. After removing the corrosion, wiped down with some WD-40 and ready to move on with the restoration. I really appreciate your help and I know that sometimes I'll have to explore on my own and figure out a solution for the future amp heads who will undoubtedly have more and more rust and corrosion as the years pass by.