oh oh i lost a channel

[ginsner]

ok i am worried now
just set up my new (to me)stereo on the weekend QUAD 33 405 and B&W DM-220's
and i just lost the right channel
I am kinda freaked as I am just trying to learn about high end and i am or rather was in love with this thing

as for what happend, I was playing Jeff Buckley at low volume when the right channel popped and quit
i swapped the speaker cables to see if it was just a fuse in the speaker itself which apperently the 220's have
but they are fine

before i start opening things up can anybody assist and give me some advice as to what to look for?

I would really appreciate the help

[anatech]

Hi ginsner,
It's obvious. It doesn't like Jeff Buckley. You're lucky, Neil Young would have caused a fire.

Unplug the 33 and do the finger hum test by lightly touching each center conductor of the RCA plug, one after the other. Hum both sides means the 33 has a problem. Hum on one side means either the cord or the amp has a problem. Repeat with another patch cable.

If the amp has a problem, unplug it and let it sit for a long while. Then carefully remove the cover. Look for fuses that are blown. If you see any badly silvered or blackened, the amp needs a good technicians hand (everyone thinks they are a technician, especially the bad ones). If the fuse glass has a little "puff" on the inside you can try another. Test the DC output voltage before connecting a speaker to it. It must less than 0.050 VDC, more means a fault.

90% of people will try another fuse hoping that's it. All they do is increase the damage, and the bill. Approach this intelligently.

-Chris

[ginsner]

I opened the 405 and yes there were puffs in fuses,
more than one of them so i am guessing the slo-blow fuses were just waiting to go
so now i have to decide where to go

[anatech]

Hi ginsner,
Well, replace them. If you have a variac, use it and watch the current as you increase the voltage. If not, you can just power it up with nothing connected, then measure the DC offset at the outputs terminals. If the fuse elements bend or glow as you turn it on, turn it off straight away.

-Chris

[ginsner]

Thanks for the advice,
normally i would have opened it up straight away and gone and replaced fuses without hesitation
but the amp came from my dad and he would be rather unhappy if I damaged it. even though he hasnt used it in years

i am assuming that the blown fuses are because of age, near 30 years of service. thats any easy fix, but then this could be an ongoing problem with other components and am considering an overhaul including published modifications
Not before alot of research and some practice doing the same to my luxman first though

oh and i did find the last repair bill which was for replacing the output transistors and it was $100 which seems rather steep
along with the bill were the old transistors as well as old slo-blow fuses (just found them) the repair was done in 03 and i dont think the amp has been used since which is suspicious and makes me wonder if something else was wrong.

[anatech]

Hi ginsner,
$100 doesn't sound expensive from a proper shop. I would worry about the repair from what you have told me.

Can you list the old part numbers and the new ones from the transistors?

One common error made is installing fast blow fuses where slow blow types are called for. I'd have to check my notes for that. Also, the heastsinks should have had the old grease completely removed (cleaned) before the new grease was applied. If the old grease just has new grease put on, or no new grease was used, the job was not done properly.

-Chris