We help IT Professionals succeed at work.

Is my power amplifier breaking?

Enabbar Ocap
Enabbar Ocap asked
on
I bought a HH s130 slave amplifier, very second hand and it was unsure if it was working. So I plugged my guitar in connected up the speakers and it works, well there is sound and it has a really nice tone too. I don't think its a full 100 watts coming out though, it's not as loud as my other 100w amp. I took the covers off and there are two large capacitors in there, 4700uF 50v electrolytics 53mm high and 35mm diameter, both of which have some serious bulges on the tops as if they are just on the point of melting.
Questions:
What are these caps for? I'm assuming that they are in the output stage as they are so big?
If they do blow can I expect 50-100v through my speaker coils and expensive damage to the speakers?
Might them being partially blown be contributing to the nice sound I am getting?
Is a guitar a high enough level input for this amp or is it expecting a line level as it is a slave amp? (There is an 'input' on the front and an 'aux input' at the back)
I will replace the caps but I want to know if its safe (for the speakers) to use it in the meantime.
Comment
Watch Question

Business Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018
Commented:
They are probably filter capacitors. They could be power supply capacitors. It is hard to say precisely what damage may occur. However, if they are as you describe, then turn off the amplifier and replace them. Do not  continue to apply power to the amplifier starting right now. The electrolyte in these is poisonous, dangerous and corrosive. Do not let them blow up.    ... Thinkpads_User
 
> poisonous, dangerous and corrosive

That has  me convinced. As well as this article that suggests that age and non-use can kill the capacitors. I've no idea when the amp was last used, but it is quite dusty as if it has been stored a long time. There is a fair amount of rust on parts of the chassis and some white powdery deposits on most of the insides. I thought this was from damp storage but maybe its from leaky caps and the amp wasn't used after a smoky incident. I'm definitely changing them now.

http://www.nmr.mgh.harvard.edu/~reese/electrolytics/
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018
Commented:
I have purchased several used electronic instruments (usually test equipment). If dry (mine have been dry), they get dusty and need to be cleaned, but no white powder. That white powder from yours is most likely from the leaky capacitors. The damp white power is conductive, so it needs to be cleaned off the circuit board. It sounds like the amplifier needs to be dis-assembled as much as possible, cleaned using distillled water most sparingly (and sometimes a solvent manually applied and again sparingly) and air dried.
 ... Thinkpads_User
ok thanks for the advice.
I'll strip it properly when I'm changing the capacitors and give it a good clean all through.
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018

Commented:
Thank you and good luck with your project. ... Thinkpads_User
Just an update and a thankyou. I found these people http://www.majelectronic.co.uk/ who have all the spare parts for H||H ampifiers. I spoke to them and they were very helpful and friendly on the phone. Ordered the parts (new caps, new rubber feet, volume pot, and even the correct coloured replacement plastic nut  for one of the jack sockets and was given good advice on how to change the parts. The parts arrived less than 24 hours from my phone call and all fitted perfectly (good price too).
My amp sounds great still, I just wanted to say thanks for the help I got here and to recommend MAJ in case anyone else is looking for parts for one of these amps.