Safe DIY way to test if an output transformer has been blown?

[Orang Goreng]

As some of you might now, recently my beloved amp (a modified 70s 100W Vibrosonic Reverb; used nothing else for over 15 years) got blown up. And by "amp" I mean the speaker, at least. We tested the resistance in the studio, and it read "infinity".

Given how it took us a while to figure out what was going on, the amp was on for a while with this speaker attached, with me turning up the volume while strumming my guitar. Guess is that while I was doing this, the OT blew because it saw an open circuit for at least some minutes.

But of course, I don't know this for sure. Maybe it's just the speaker. The amp could be fine otherwise. I noticed today that the caps (which I identified as the likely culprit) don't show any signs of leaking, swelling, or otherwise. They look pretty much new, so I don't think any of them failed.

Before getting a tech to look at the whole thing, I'd like to know if there's a safe way to test if the OT is OK or not. I bought an identical (but working ) amp recently... is it safe to simply hook up that speaker to the broken-down amp and see if it makes noise? Or is that a potential way to blow up my new speaker? Is there perhaps something I can test with a multi-meter? (I've been looking for an excuse to buy a new one)

TIA,
Z.

[Orang Goreng]

Thanks øøøøøøø, I was hoping you'd reply .

Sometimes people tend to think of them as these great mysterious things, but... if no signal is going to the speaker, what could hurt the speaker?  Smiley Smiley Smiley

Well, if I gave you any idea I have anything remotely resembling tube amp knowledge, I apologise . I don't really know what "a blown output transformer" really entails... for all I know it passes MORE current now. I guess that's not too logical indeed, no....

Well, that's very cool! It's a bit late in the evening to give it a try, but I will tomorrow.

Heh, if this means all I'm looking at is a speaker recone, all this may not be so bad after all....

[Orang Goreng]

I don't want to start yet another thread about my amp situation, so I'll post this here... I just found this DIY recone set on-line. Does this seem good?

Please keep in mind that
- I have a tendency to be a complete idiot at times
- I'm very good with precision work at the semi-microscopic level
- I'm crap at anything that requires work at the somewhat larger level, unless it's assembly of pre-made kits.

http://www.soundspeakerrepair.com/speak ... /JBL+Kits/

[Orang Goreng]

OK, just tested it... the old amp's fine indeed! I hooked it up to the new D130F, and the old sound was there straightaway. Phew!

I re-tested the old speaker with my ratty, half-working multimeter. It can still read Ohms and DOhms, so the usable range is still there. Speaker cable is perfectly fine, but I get an infinity reading when I test at the jack, the attcments of the speaker wires, and the wires themselves.

So... partial Yay! Thanks, øøøøøøø!

About that recone... yeah, that's tricky. I found a number of local(ish) recone services, but they all seem to cater to the HiFi market, which may mean I'd have to buy the recone set anyway and just hire them to install it. But if you're serious about that reconed D130...heck yeah I'm interested, though that's something best discussed over PM. Shipping such a mofo can't be cheap...

Anyway, thanks again!

If that's not the case, you may have an open voice coil winding.  I'm not a speaker expert, but I don't know what you would do for that.  A recone wouldn't fix an open voice coil though.  My best advice in that case would be to e-mail Ted Weber, from his website at www.tedweber.com

Here's my limited knowledge rearing its head again. I recently learnt (yeah, really ) that the coil is glued to the cone. The re-cone set has a new voice coil in it. Wouldn't that take care of the problem?

[øøøøøøø]

try this:

Get a 9v battery and BRIEFLY connect the two terminals of it to the two speaker terminals of the dead D130.  You should get an enthusiastic "pop" as the speaker excurses IF the voice coil is OK.

Remove the battery quickly so as to not overheat the voice coil if it is still good (speakers don't like DC across them for long periods, but it will be fine for a second or two to test).

PM about the D130 is on its way. 

[Orang Goreng]

PM'd back .

Yeah, the company in the link makes a big deal out of the fact that they use flat..something..aluminium rather than copper usually found on recone kits. Apparently. Can't really tell if this is relevant or marketing blurb, but at any rate, yeah, there's a coil in there which has to be dropped in and aligned with the voice coil gap.

Hey, if Jay hadn't educated me a bit about speakers when the thing first broke, I'd still be thinking the sound is produced by a pixie living in that bell structure with the little mesh-covered hole (which I assume is there to allow the pixie to breathe).

[øøøøøøø]

yes.  Flat aluminum ribbon wire is the correct voice coil wire for that speaker. 

[Orang Goreng]

Cool.

Funny.. I've had the new amp for over a week now, transplanted cabs on it, but only today I actually TRIED it out.. I just never play plugged-in at home, so somehow it never came of it. I heard it when I bought it though.

Anyway...wow. I know not a lot of people like the OD that comes from the pre-amp on a master volume silverface, but that thing on 10 with a bit of reverb, driven by the humbuckers in my SG...great sound. Actually, I prefer the way these things sound at a very low volume over the way they sound when they're cranked. They're just a bit too trebly then, which I guess is what sets them apart from the non-master-volume models.

STILL haven't tried it with the JMs...

[mynameisjonas]

Anyway...wow. I know not a lot of people like the OD that comes from the pre-amp on a master volume silverface, but that thing on 10 with a bit of reverb, driven by the humbuckers in my SG...great sound.

that sound is the heart and soul of UDDUP, both me and mattias mainly used his 135W SF twin on our recordings