fran604g Posted March 23, 2019 Report Share Posted March 23, 2019 Hiya folks, I'm in the midst of replacing the pots in both of my AR3a's and in addition to the bad pots, I also determined that one of the tweeters has failed. It measures at 1.0 ohm - so I'm thinking either an internal short or something has occurred. But, after removing the tape that holds the leads in place (hoping the problem was there - which it wasn't), I realized that the leads for the tweeter are connected backwards in relation to the position of the large red "+" sticker on the mounting ring of the tweet. I consulted the rebuild guide, and on page 11, fig. 3.6, the wiring is illustrated to be the same as mine is connected. Maybe this has been addressed elsewhere on the forum, but is this correct? Why would the positive sticker have originally been placed at the negative lead side of the tweeter? Was this wired out of phase? Link to comment Share on other sites More sharing options...
Chris1this1 Posted March 25, 2019 Report Share Posted March 25, 2019 Hi Fran, I can shed some light on this. The tweeter is not actually wired out of phase, if it was a working example, you will see that the + lead is still on the right after crossing by a simple 1.5v battery test(dome will push away from base when + of battery attached to + lead on right). Must have been crossed to correct polarity during tweeter production, which seems common (I see a lot of these tweeters from rebuilding). Crossed or not, they keep the + on the right from what I have seen. Chris Link to comment Share on other sites More sharing options...
fran604g Posted March 25, 2019 Author Report Share Posted March 25, 2019 Thanks, Chris. Link to comment Share on other sites More sharing options...
RoyC Posted March 25, 2019 Report Share Posted March 25, 2019 What Chris said... Make sure to replace the tape between the leads to prevent shorting. Roy Link to comment Share on other sites More sharing options...
fran604g Posted March 26, 2019 Author Report Share Posted March 26, 2019 The thing that tripped me up is the illustration in the guide (pg.11, fig.3.6, "Front-wired terminal block). It clearly shows positive as being on the left side of the tweeter. My tweeter was wired to the diagram, counter to the actual labeling of my tweeter, i.e. reversed polarity. I don't think I switched the leads when I repaired it in 2012, so presumedly it was wired this way in the factory. Or not. I just obsess sometimes over the "why", when I should simply concentrate on the "do". It doesn't really matter all that much, both will be wired to the schematic once I get them back from Chris. Link to comment Share on other sites More sharing options...
fran604g Posted March 26, 2019 Author Report Share Posted March 26, 2019 Oh, and what about fusing? I use these with my TAD 60 amp, which might over power them. Currently I'm using Tung-Sol 6550 reissues for output tubes. I would estimate output to be in the neighborhood of 50-60 wpc. If this is the reason behind the tweeter failing, I'd obviously prefer to prevent a repeat occurrence. That being said the other speaker still functions. Link to comment Share on other sites More sharing options...
RoyC Posted March 26, 2019 Report Share Posted March 26, 2019 5 hours ago, fran604g said: The thing that tripped me up is the illustration in the guide (pg.11, fig.3.6, "Front-wired terminal block). It clearly shows positive as being on the left side of the tweeter. My tweeter was wired to the diagram, counter to the actual labeling of my tweeter, i.e. reversed polarity. I don't think I switched the leads when I repaired it in 2012, so presumedly it was wired this way in the factory. Or not. I just obsess sometimes over the "why", when I should simply concentrate on the "do". It doesn't really matter all that much, both will be wired to the schematic once I get them back from Chris. All AR-3a front-wired tweeter leads I have seen were originally crossed under the tape as shown in the guide, and the actual + side of the tweeter's voice coil is as shown in the AR-3a guide's illustration. As seen on Fran's tweeter, for a period of time, AR confusingly placed a + sticker on the side of the tweeter to which this lead was routed under the tape. I have, in fact, seen AR -3a tweeters with red + labels on both sides...and many more with no sticker at all. When these tweeters became back-wired in the mid 70's the + side remained on the left (when viewed from the front). Roy Link to comment Share on other sites More sharing options...
Aadams Posted March 26, 2019 Report Share Posted March 26, 2019 Now I am confused 1 hour ago, RoyC said: All AR-3a front-wired tweeter leads I have seen were originally crossed under the tape as shown in the guide, Roy are you saying this is normal for front wired AR3a tweeters. Of the four I have removed only one has been crossed. Adams Link to comment Share on other sites More sharing options...
fran604g Posted March 26, 2019 Author Report Share Posted March 26, 2019 2 hours ago, RoyC said: All AR-3a front-wired tweeter leads I have seen were originally crossed under the tape as shown in the guide, and the actual + side of the tweeter's voice coil is as shown in the AR-3a guide's illustration. As seen on Fran's tweeter, for a period of time, AR confusingly placed a + sticker on the side of the tweeter to which this lead was routed under the tape. I have, in fact, seen AR -3a tweeters with red + labels on both sides...and many more with no sticker at all. When these tweeters became back-wired in the mid 70's the + side remained on the left (when viewed from the front). Roy Thank you Roy, that explains it. That's great. Fran Link to comment Share on other sites More sharing options...
RoyC Posted March 27, 2019 Report Share Posted March 27, 2019 8 hours ago, Aadams said: Now I am confused Roy are you saying this is normal for front wired AR3a tweeters. Of the four I have removed only one has been crossed. Adams Yes, crossed under the tape is normal for the 3a and the 5, as shown in your photo. The center terminal represents the + side of the crossover, and is also where the mid + side is connected. It is where all those yellow wires inside the cabinet end up. Roy Link to comment Share on other sites More sharing options...
Dchristie Posted March 28, 2019 Report Share Posted March 28, 2019 And not to confuse (hopefully) the issue further, but all of the Chris 1 REBUILT AR 3a tweeters that I have received from Chris ( 4 pairs to date) have had the positive lead of the tweeter on the RIGHT side of the tweeter faceplate (when viewed straight on) which would then NOT require the leads to be crossed under the tape when resoldered back to the middle tabs on the cabinet front. Chris has the ability to place the leads wherever he sees fit when he does his rebuilds and usually places the + lead on the right side. As Roy has stated above, the key is to make sure the + leads from both the mids and the tweeters are always soldered to the tabs where the yellow wires are attached from the xover. (I have also had one each of both pairs of the mids on my AR 3a and AR 5's crossed under the tape as well). And as Chris has also stated above , the most prudent thing to do to verify which lead is + or - is to do a battery test and confirm the dome moves up (when the positive lead is attached to + battery terminal and negative lead is attached to the - battery terminal) or down if the leads to the battery terminals are reversed. Although not always easy to see on old, original tweeters due to their stiffened suspensions, it is easy to see movement on Chris's rebuilds and can often even be seen on original tweeters with the help of some magnification. Dean Link to comment Share on other sites More sharing options...
fran604g Posted March 28, 2019 Author Report Share Posted March 28, 2019 Thanks Dean. I've sent both tweets to Chris, so I'm sure the polarity will be maintained. It's funny to me that the OEM would be so confusing. But stranger things I've seen in my lifetime. Link to comment Share on other sites More sharing options...
RoyC Posted March 29, 2019 Report Share Posted March 29, 2019 6 hours ago, fran604g said: Thanks Dean. I've sent both tweets to Chris, so I'm sure the polarity will be maintained. It's funny to me that the OEM would be so confusing. But stranger things I've seen in my lifetime. To make it even more interesting, some (not many) early AR-3a and 5 mids' leads were also crossed under the tape. I have checked a few of these mids with the metal grill removed, and found the + side of the voice coil to be on the opposite side of their later brethren, necessitating the crossed leads. In the absence of verification, however, the general rule of thumb is the left voice coil lead of front-wired 3a/5 tweeters and mids are + when viewed from the front. This is true of the later back-wired versions of these drivers as well. Earlier drivers have a greater chance of variation. Polarity of AR woofers varied more than the tweeters or mids into the mid 70's, so it is prudent to check them as well Roy Link to comment Share on other sites More sharing options...
fran604g Posted March 29, 2019 Author Report Share Posted March 29, 2019 Roy, Out of curiosity, what have you discovered with the mid range drivers? Also, how would I be able to determine whether the phasing is correct with them? My apologies if this topic has been explained elsewhere. Fran Link to comment Share on other sites More sharing options...
Dchristie Posted March 29, 2019 Report Share Posted March 29, 2019 Hi Fran, as Roy stated above, even the front wired 1.5 dome mids may have the leads reversed with respect to the left or right side of the faceplate. Since the mids handle lower frequencies compared to the tweeters, the movement of the dome is much more noticeable ( especially with the metal grill removed). I have found this to be occasionally true with the very early midranges , and in my case, only one of the mids in the pair was reversed. Since Roy has dealt with many more mids ( and tweeters) he may have a better feel for how commonly this lead reversal occurs . Although It is not easy, it is possible to see the dome move with the battery test . I position the midrange driver so that a bright light source reflects off the dome surface where it can be observed between the damping material attached to the metal screen ( usually the best place to see the dome is near it's base ) . The dome surface is somewhat shiny and any imperfections on the surface of the dome can provide a point of reference for the light reflection. I usually also use reading magnifying glasses to help see the movement . Although not dramatic, applying the 1.5 volts to each of the leads does show the reflected area of the dome move up or down as per the + or - characteristic of the respective leads. Dean Link to comment Share on other sites More sharing options...
fran604g Posted March 29, 2019 Author Report Share Posted March 29, 2019 Thanks Dean, visual inspection was a problem. I simply cannot tell which way it's moving. Fran Link to comment Share on other sites More sharing options...
RoyC Posted March 29, 2019 Report Share Posted March 29, 2019 Fran, The vast majority of mid and tweeter leads are as described in my last post. If there is a departure from the norm (tweeters' crossed/mids' not crossed) you will see the original position of the leads under the tape on the driver itself. Just go with the position of the leads as you find them. If you are using tweeters rebuilt by Chris, ask him to identify which side is + if he hasn't already done so. Bear in mind, only the earliest front-wired mids may have crossed leads, and there is no known reason to uncross them. Removing the grill is not recommended unless you have a solid reason to believe the mid has been tampered with. Based on the photo you posted above, there is no reason to be concerned with the installation of that mid. The + sign and lead are clearly where they should be. Roy Link to comment Share on other sites More sharing options...
fran604g Posted March 29, 2019 Author Report Share Posted March 29, 2019 Thank you, Roy, that's what I'll go with. Link to comment Share on other sites More sharing options...
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