AR3a Tweeter Revalation

[oldarnut]

Today, I finally reached the end of my patience with one of my AR3a's. I use them for rear surrounds in my home theater system. On one of the AR3a's, the pots for mid and tweeter were very intermittent so I decided to clean them. I removed the woofer, fiberglass, and porcelain pot cover and went cleaned the wiper and coiled resistor element with #400 emery cloth. When I snapped the porcelain covers back on, the mid and tweeter worked immediately without diddling with the adjustment knob!! But, the tweeter output was very low, even with the level control turned all the way up.

I remembered I had some spare tweeters that Dynaco Dan sent me several years ago, so I dug one of them out, checked it for continuity. It measured right around 3 ohms DC resistance with a healthy "pop" as I touched the meter leads to it. I soldered the leads of this tweeter in place of the "quiet" one, stuffed the fiberglass back in along with the woofer.

As I suspected, the system sounds like I remembered AR3's from years ago. You now don't need a toilet paper roll to hear the tweeter--you can actually hear it when you stand in front of the speaker.

The one I removed has a date of May 30, 1975 on it, so it appears this was a replacement unit from AR. There are no numbers on it. The one I installed was manufactured in 1973--don't remember the month and day.

The flexible material that holds the dome, including the three little dabs of what feels like silicone rubber, feels resilient and the dome appears to be secured by this material. Resistance is the same as the tweeter I put in its place--about 3 ohms DC.

I snapped some pictures of the tweeter I removed and attached them.

[dynaco_dan]

I remembered I had some spare tweeters that Dynaco Dan sent me several years ago, so I dug one of them out, checked it for continuity.

Hi there

Weren't me my friend.

[oldarnut]

Sorry, typo on "revelation." I really do know how to spell it.

Also, I forgot to mention that I was doubting my memory of how these speakers sounded when new--and thinking maybe my high freqency hearing was worse than I thought. This doubt sas strengthened by recent posts suggesting the tweeters put out very little sound due to this high crossover frequency. While I can no longer hear above 19Khz as when young, I thought there should be at least noticeable output above the tweeter crossover point (5500 hz?). Well, the memory was right. The new tweeter makes the system sound as my memory said it should.

AR3's rock---just as they did in 1969!

[oldarnut]

The spare tweeters did not come from dynaco__dan. I found the box they were shipped in dated 2003. The label is faded, but the name looks to be Edward Arnold from Pennsylvania. I think he removed the six tweeters from an ARLST and replaced them with somethine else. Anyone know of his whereabouts so I can thank him again?

[RoyC]

Also, I forgot to mention that I was doubting my memory of how these speakers sounded when new--and thinking maybe my high freqency hearing was worse than I thought. This doubt sas strengthened by recent posts suggesting the tweeters put out very little sound due to this high crossover frequency. While I can no longer hear above 19Khz as when young, I thought there should be at least noticeable output above the tweeter crossover point (5500 hz?). Well, the memory was right. The new tweeter makes the system sound as my memory said it should.

Glad you got your 3a's working properly! Wouldn't comparing your two speakers have told you something wasn't right about the one with the bad tweeter?

Whatever the case may be, variable output is a problem with the old tweeters these days. The likely reason for the low output of your bad tweeter is crumbling foam under the dome getting into the voice coil. The orange blobs on the outside of the dome are also comprised of polyurethane foam covered by a butyl rubber compound, which serves as the suspension. This can be deteriorated as well, though it does not appear to be the problem in your case.

The original tweeter indeed has far less output at lower frequencies than modern tweeters, which often makes people think there is a problem. This is a different issue than the deterioration described above. The original tweeter's output above 5000hz is actually quite strong (when functioning properly).

Roy

[oldarnut]

The other AR3a in my home theater system already had a morphodite tweeter installed by the previous owner. It does not sound like I thought an AR3a should sound, so I'm going to see if one of the other spare AR tweeters marked "Good" will work as good as the one I installed yesterday. If I find a good one, I'll have two good-sounding AR3a's. If not, Hi-Vi Parts Express is the next step.