Hello there everyone. This is my first thread on this forum, just thought I would post my progress on an HK A500. This is the first amplifier I have attempted to restore so I am bound to make a bunch of mistakes and whatnot.
Sorry about the image quality on some of these, photography is not my strong suit.
1.
After taking it apart for the first time, the face plate was caked in dust and I had to vacuum out about a cup full of mouse turds. There seemed to be quite a bit of rust on the surface as the amp spent most of its life in New York.
2.
I got a better camera and moved into a new apartment. This is after cleaning and polishing the face plate.
3.
Cleaned all the dust and grime with 70% isopropyl alcohol. There is a good amount of cooked on grime and rust on the chassis. As of now I don't want to drill all of the rivets out and replace all of the components so I am going to attempt a cleaning with the sockets, transformers, and psu caps in place (although I will replace the supply caps and leave the originals as dummies).
4.
Pulled off the bottom plate, the inside looks great and there aren't too many caps that need to be replaced. I will do all of the electrolytic and paper-foil types. The .25uF caps I will probably replace with .22uF. I believe they are the coupling caps on the output stage so I might lose a little low end, but then again, .22u is a 12% deviation from .25u which, i would guess, is better than the tolerance of the paper-film caps. (Correct me if i'm wrong 😀)
5.
I took the rust and grime off with some 400 grit paper and began to polish it up with 1200 grit. I am sure that I am botching this part, if anyone has some tips they would be greatly appreciated.
Also let me know if this whole method of putting in pictures and my steps is annoying, like I said this is a first for me. Advice is more than welcome.
Sorry about the image quality on some of these, photography is not my strong suit.
1.
After taking it apart for the first time, the face plate was caked in dust and I had to vacuum out about a cup full of mouse turds. There seemed to be quite a bit of rust on the surface as the amp spent most of its life in New York.
2.
I got a better camera and moved into a new apartment. This is after cleaning and polishing the face plate.
3.
Cleaned all the dust and grime with 70% isopropyl alcohol. There is a good amount of cooked on grime and rust on the chassis. As of now I don't want to drill all of the rivets out and replace all of the components so I am going to attempt a cleaning with the sockets, transformers, and psu caps in place (although I will replace the supply caps and leave the originals as dummies).
4.
Pulled off the bottom plate, the inside looks great and there aren't too many caps that need to be replaced. I will do all of the electrolytic and paper-foil types. The .25uF caps I will probably replace with .22uF. I believe they are the coupling caps on the output stage so I might lose a little low end, but then again, .22u is a 12% deviation from .25u which, i would guess, is better than the tolerance of the paper-film caps. (Correct me if i'm wrong 😀)
5.
I took the rust and grime off with some 400 grit paper and began to polish it up with 1200 grit. I am sure that I am botching this part, if anyone has some tips they would be greatly appreciated.
Also let me know if this whole method of putting in pictures and my steps is annoying, like I said this is a first for me. Advice is more than welcome.
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Hi, i wish i had could have let you known sooner about the plating that they used on the steel, i believe it is cadmium and is a toxic substance. So you should be wearing protective equipment , respirator, gloves, when you are sanding and try not to get the dust everywhere. I did a chassis with rust on it by painting it with special epoxy paint that seals in the rust. Other people use a "rust converter" chemical which turns rust inert. Which you can paint over. Other than that very nice work and good luck with your project.
Thanks DAK808, I got some of the dust in my nose and it stung pretty bad. After that I got the respirator and gloves. Thanks for the heads up and advice, i'll look into the epoxy paint.
Once sorted out this should be a very nice sounding amp. I've not had good experiences with the American Radionic caps in terms of reliability, they seem to become intermittent in some cases - otherwise they are pretty good caps. The ones I have disassembled were film and foil, the problem arises with the terminations which seem to work over time due to differing coefficients of expansion between the ceramic tube they're in and the capacitive element itself. (Just a swag on my part)
You might find this useful.
Richard Sherman
Long ago I owned an A700 (late 1970s) and have for decades regretted parting with it. Possibly the best sounding integrated tube amp I have ever owned. (Or maybe the HH Scott 296? LOL)
Richard Sherman
Long ago I owned an A700 (late 1970s) and have for decades regretted parting with it. Possibly the best sounding integrated tube amp I have ever owned. (Or maybe the HH Scott 296? LOL)
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