I'm in the process of restoring a 40+ year old un-molested power amplifier. It works, sounds great and has almost no DC offset on the speaker terminals.
I found two mica capacitors (30pF and 120pF) both of which have a dark spot in the middle. Not sure if that is a burn mark or just color aging with time.
Question - do mica capacitors degrade with age or is this due to heat and I need to replace them?
Rgds
Mayank
I found two mica capacitors (30pF and 120pF) both of which have a dark spot in the middle. Not sure if that is a burn mark or just color aging with time.
Question - do mica capacitors degrade with age or is this due to heat and I need to replace them?
Rgds
Mayank
Attachments
Mica capacitors are one of the most stable materials for capacitor dielectric, it shouldn't be easy to make those parts fail in that kind of applications. The brown part you say is cause they are dipped in colored epoxy/silicone resin and then are made to drip the excess
Last edited:
Thank you for your explanation re epoxy/resin. I will leave them in place and just focus on replacing the bead tantalum and electrolytic capacitors.
Rgds
Mayank
That power amp appears well built, who is the manufacturer?
If it's working well I'd be tempted to leave well alone.
If it's working well I'd be tempted to leave well alone.
This is a BGW-250D pro-audio power amplifier from the early 1980's. It is very well built and in great condition inside.
I was introduced to BGW amplifiers when I came across their flagship BGW-750A power amplifier which was retired from service at Universal Studios, Hollywood. It was built in mid 1970's for the production of the movie "Earthquake", which introduced Sensurround to the world - a few years before Lucas used surround sound in Star Wars. I spent several months carefully restoring and rebuilding it for home use with a lot of help from members here and at AudioKarma. The progress was documented here:
BGW 750A - Restoration | Audiokarma Home Audio Stereo Discussion Forums
I am now in the process of restoring its younger sibling the 250-D which I rescued from a recording studio which unfortunately went out of business.
These are great (designed, sounding & built) amplifiers, especially after the refresh/upgrade.
Rgds
Mayank
I was introduced to BGW amplifiers when I came across their flagship BGW-750A power amplifier which was retired from service at Universal Studios, Hollywood. It was built in mid 1970's for the production of the movie "Earthquake", which introduced Sensurround to the world - a few years before Lucas used surround sound in Star Wars. I spent several months carefully restoring and rebuilding it for home use with a lot of help from members here and at AudioKarma. The progress was documented here:
BGW 750A - Restoration | Audiokarma Home Audio Stereo Discussion Forums
I am now in the process of restoring its younger sibling the 250-D which I rescued from a recording studio which unfortunately went out of business.
These are great (designed, sounding & built) amplifiers, especially after the refresh/upgrade.
Rgds
Mayank
The only thing I'd do if it were mine would be to clean the flux off the connections that were made (power transistors, wires) after the PCB was mounted to the heatsink.
Bit of isopropyl, and a toothbrush, and it'll clean up beautifully.
You see this so often on boards. The stuff that was done in the wave soldering machine is pristine, because the board goes through a wash afterwards. Then there's those last few connectors or pots or what-have you that are put on by hand afterwards, and they're a filthy mess.
Bit of isopropyl, and a toothbrush, and it'll clean up beautifully.
You see this so often on boards. The stuff that was done in the wave soldering machine is pristine, because the board goes through a wash afterwards. Then there's those last few connectors or pots or what-have you that are put on by hand afterwards, and they're a filthy mess.