Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: BobL on February 26, 2021, 10:07:57 pm

Title: How to test/repair speaker?
Post by: BobL on February 26, 2021, 10:07:57 pm: I bought a pair of used Celestion Blues for a build, and one of them seems to be dead. I have them wired in parallel - going to the first speaker, then from the first speaker to the second... and the first speaker is the dead one, while the second speaker makes noise but seems to have some strange overtones, which maybe could be from the first speaker?

Amp into other speakers works just fine...

It's been a bit since I bought them since I yanked what I originally built and did something else, so a return might be tricky, and wondering what I can do to troubleshoot from my end.

Two 8 ohm speakers, I'm measuring about 3.2ohms, which is about what I'd expect, so I don't think I've got a disconnected wire.

Thanks!
Title: Re: How to test/repair speaker?
Post by: PRR on February 27, 2021, 12:09:34 am: Measure the Ohms of each speaker separately, in a quiet room.

You expect the DC Ohms to be 80% of the Audio Ohms.

You can normally hear the "skkiritch" of the ohm meter's test current in the speaker.

Then try each speaker *separately* on a healthy amplifier. It is OK to run a 8 Ohm load on a 4 ohm amplifier, if it is NOT loud and not for long. Does it play some quiet-to-medium clean strumming OK? How about the other one?
Title: Re: How to test/repair speaker?
Post by: BobL on February 27, 2021, 09:21:21 am: I can't hear anything with that speaker on its own w/ the MM, but I'm getting 6 ohms on it.

By itself with the amp I actually can get some noise out of the speaker (maybe I was before and the other one was just so much louder I couldn't tell), but it's super noisy and thin and quiet...
Title: Re: How to test/repair speaker?
Post by: acheld on February 27, 2021, 09:56:42 am: Is the voice coil rubbing?
Title: Re: How to test/repair speaker?
Post by: BobL on February 27, 2021, 10:16:26 am: Quote from: acheld on February 27, 2021, 09:56:42 am
Is the voice coil rubbing?

Why yes, it is... badly, it would seem.

This doesn't look serviceable w/o removing the spider?
Title: Re: How to test/repair speaker?
Post by: BobL on February 27, 2021, 10:25:30 am: Going to see if I can get the seller to take it back... ordered a month ago today, so hopefully I don't get told to take a hike.
Title: Re: How to test/repair speaker?
Post by: PRR on February 27, 2021, 12:33:09 pm: Sudden rub on a "new" "just bought" speaker suggests the magnet shifted in shipping. I've never seen a home repair for a large magnet shifted.
Title: Re: How to test/repair speaker?
Post by: BobL on February 27, 2021, 12:36:28 pm: Quote from: PRR on February 27, 2021, 12:33:09 pm
Sudden rub on a "new" "just bought" speaker suggests the magnet shifted in shipping. I've never seen a home repair for a large magnet shifted.

Yeah, it's a used speaker, so I'm not sure. It was not especially well packaged. :/
Title: Re: How to test/repair speaker?
Post by: acheld on February 27, 2021, 08:46:42 pm: If the seller won't take it back, you could do a tear down and see what you've got.

Although not especially popular on this forum, Uncle Doug has a couple of videos on speaker repair and reconing that are pretty good, I think.