Why doesn't this AR5 tweeter play?

[prrtraincow]

I have a nice old pair of AR5s. I haven't been using them

much, and I just notice that neither tweeter works. They definitely used to. Back in 1981, I replaced them both after somebody carelessly

blew them up using the speakers at a party. They've played great ever since.

I disconnected the tweeter and the mid on the front solder tag strip.

If I connect the mid to the mid terminals, it plays. If I connect it to

the tweeter terminals, it plays. If I connect the tweeter to

either terminal pair, it does not play.

So, I was pretty convinced that the tweeters were dead (although I can't imagine why, since I rarely play these speakers and never all that loud). I drive them of a Dynaco stereo 80 solid state amp with a PAT-4 preamp.

But here's the puzzling thing. An ohmmeter reading on the tweeter reads

5.9 ohms, which seems just about right. I would have expected it to be "open" (infinite) if the coil were burned out.

What else could keep the tweeter from playing?

[dynaco_dan]

Hi there;

First, I would suggest that you re-connect the leads back up as they were originally.

After that, turn the pots back and forth numerous times to sort of self-clean them, some what.

With a source of music or sine waves you should begin to hear output if you have the pots set at maximum, or while turning them back and forth.

[frankmarsi]

I think it's obvious, it's the pots, it's always the pots. Could be a leaking cap also? Could be your electronics? Could be some atmospheric grime here or there?

FM

[prrtraincow]

Please note:

If I hook the midrange driver up to the tweeter terminals on the front panel, the midrange PLAYS. So the tweeter terminals have signal on them. If I hook the tweeter to those same terminals, it does NOT play. So it has to be the tweeter driver. If it was the pot, the

midrange driver wouldn't play either, when connected to the tweeter terminals. And yes, I moved the tweeter pot back and forth while I had the midrange hooked to the tweeter terminals, and the level goes up and down like it should. The pot isn't corroded.

My puzzlement is over how the tweeter could not play when it has a 6 ohm resistance. I would have expected it to be an open circuit.

[rrcrain]

Check the resistance from either terminal to the frame. Perhaps the voice coil overheated, warped and is bound in the magnet gap? Failing that, test the speaker with a signal generator. If it works with a sig gen, the problem is definitely with the crossover.

[dynaco_dan]

Hi there;

A quickie and safe test is, if you have access to just the drivers 2 lead outs, use a 1 1/2 volt battery, no higher voltage, to test it.

This will tell you if the driver is or isn't any good.

[prrtraincow]

I received my replacement tweeters (off Ebay) today. Each of them plays if I hook it to the tweeter terminals on my AR5s, where the current tweeters would not play. So, it's definitely the tweeters.

But I played them on very low volume just to make sure they work.

I am going to replace all the crossover capacitors before I connect these in for good. I suppose if the 4uF series caps that protect the tweeters are going bad, or are shorted, that could have fried the tweeters I had in there.

[rrcrain]

I'm not familiar with this particular tweeter so someone feel free to disagree.

If the original tweeters are repairable, I'd suggest doing so if nothing else so you have a set of backup tweeters.

[RoyC]

The tweeters are identical to the AR-3a tweeter, but are higher impedance versions that were used in the AR-5 and (later) AR-2ax.

They have the old urethane foam/butyl rubber coated suspensions. For all practical purposes, they are not repairable.

Roy

[dynaco_dan]

Hi Roy;

I will now add my small comment to this topic.

There was an Asian man, perhaps Korean, who was working on repairing them a year or so ago.

I never heard anymore about that project.

There was several photos of the domes and magnets in his write-up.

Otherwise, you are absolutely correct, unless we have a new genius, an inventor type member, come on board with that experience.

Irregardless, I would take good care of them, as if they can be repaired, in a box, for possible future repairs or credit towards that end.

[kkantor]

While an open circuit is the most common failure mode, there are others. For example, the tweeter's coil can become detached from the diaphragm, resulting in almost no sound output, but fairly normal electrical impedance. The coil can "shuck" a few turns of wire, and become jammed, too.