Elialan Posted January 18, 2021 Report Share Posted January 18, 2021 Hi everyone! I'm Elia from Italy, I'm new to this forum and I'm just working on a pair of magnificient AR3, which have been appeared in Italy in the early '60 from a NATO base. The speakers have been forgotten for a very long time and the boxes have some dents and need a restorations, but the loudspeakers are all original and in working condition. After almost 55 years, the capacitors need to be replaced. And here is the question. My speakers have a serial number C22312, so according from the reference article here in classic speaker pages, they have a crossover topology 'C', where the midrange and tweeter are filtered only by a capacitor, without any inductor. However, looking at the crossover the stamped date seems to be JUN 11 1963, so the crossover topology must be the'B'. Any advice on this incongruence? And then another doubt..... One woofer bolt is missing. What is the thread of the woofers bolts? Elia Quote Link to comment Share on other sites More sharing options...
RoyC Posted January 18, 2021 Report Share Posted January 18, 2021 The added inductor is not in your photo, so it is not an issue. I presume your mids have rounded magnets (?). Post a photo of them. The woofer screw is a 1/4-20 fillister head screw. Roy Quote Link to comment Share on other sites More sharing options...
Elialan Posted January 19, 2021 Author Report Share Posted January 19, 2021 Very good for the screws, now here in Italy will be a very hard challenge to find them! The midrange magnet structure is noot the rounded one, but they are the squared one, which according to the article, are correct for the period. Regarding the L-Pad, they are quite oxidated and expecially one cursor has rusted. I have some spare L-Pad coming from a couple of AR 2AX speakers. Seems that they are equivalent, is that so? My idea is to replace only the internal cursors and the ceramic part which houses the resistance and the contacts. Quote Link to comment Share on other sites More sharing options...
Elialan Posted January 27, 2021 Author Report Share Posted January 27, 2021 The pots that i think were good, shows great corrosion, so they are useless. I've found four 16 ohm, 50 watt vintage rosenthal (yes, the one of fine ceramics!!!) N.O.S. for cheap (50$ for the whole bunch). Do you think that they are good enough? Quote Link to comment Share on other sites More sharing options...
Aadams Posted January 27, 2021 Report Share Posted January 27, 2021 3 hours ago, Elialan said: I've found four 16 ohm, 50 watt vintage rosenthal (yes, the one of fine ceramics!!!) N.O.S. for cheap (50$ for the whole bunch) Those are nice looking. Can you not use Lpads with resistors? Quote Link to comment Share on other sites More sharing options...
Elialan Posted January 27, 2021 Author Report Share Posted January 27, 2021 I've read something about L-PADS in classical ARs. However, since the pair that I am restoring one of the second gen of AR3, I prefer to use rehostats to have a more historically correct result. Obviously L PADS are more reliables, if one day I'm going to restore a pair of AR3A for example, I will use them. Just a curiosity. Ive seen some ebay adverts for classical AR rehostats. The seller claim that LPADS in classical AR usually last for at least 6 months and then they melt. Is that true? If we put the parallel resistor to the load, i cannot see the problem to use them. Quote Link to comment Share on other sites More sharing options...
genek Posted January 27, 2021 Report Share Posted January 27, 2021 These will work electrically, but you will need to add some kind of housing or shroud to shield the open windings so the cabinet stuffing doesn't get into them. Also, because the originals were 15 ohm units. the center dot will no longer be the correct "Normal" setting. You can adjust for this by measuring the resistance, setting each unit to the "Normal" value in the restoration guide and placing the control so that setting is aligned with the center dot. Quote Link to comment Share on other sites More sharing options...
Elialan Posted January 27, 2021 Author Report Share Posted January 27, 2021 Yes, I think i'll go to design a cover which i'll fix in the center of the shaft in the rear of the rehostat. It will be designed as a disk whose diameter is exactly the external diameter of the rehostat itself, to protect the contact. The aetna pollak which I have measures 16 ohms. Since they are linear pot, if the dot corresponds to the middle of the resistance value, i think that I have no problem. Quote Link to comment Share on other sites More sharing options...
genek Posted January 27, 2021 Report Share Posted January 27, 2021 The dots never corresponded to the middle of the resistance values. The 3a restoration guide specifies what the resistance should be at the center dot for the mid and high controls. Note that mid and high controls have different resistance values for their respective dot positions. Quote Link to comment Share on other sites More sharing options...
Elialan Posted January 27, 2021 Author Report Share Posted January 27, 2021 I m a poor student, sorry! I've read now about the pots positioning! :) is the reference position equal between the AR3 and AR3A? Quote Link to comment Share on other sites More sharing options...
genek Posted January 27, 2021 Report Share Posted January 27, 2021 Good question. Have never heard anyone say they are not. Ultimately, though, most people set their levels by ear and the main reason to align the dots with specific R values is to ensure that all of your speakers are set up the same. Those pots have a pretty loose tolerance and the same position on any two will often not be the same resistance. Quote Link to comment Share on other sites More sharing options...
Elialan Posted January 27, 2021 Author Report Share Posted January 27, 2021 I think the tolerance is the point.... in mine I have several ohm between the solder tabs and the corresponding brass rivets inside the pots. However I'll go with the settings in the reference article! Quote Link to comment Share on other sites More sharing options...
JKent Posted January 28, 2021 Report Share Posted January 28, 2021 23 hours ago, Elialan said: Just a curiosity. Ive seen some ebay adverts for classical AR rehostats. The seller claim that LPADS in classical AR usually last for at least 6 months and then they melt. Is that true? Not true. Absolute nonsense. In fact, AR switched over to L-pads on some models (maybe the 3a Limited or 3a Improved). That guy sells some nice looking pots but I don't trust anyone who makes false claims. Those Rosenthals look very nice. Just be sure there is enough room to fit them (I'm sure you already checked) and remember Gene's advice: They will need some kind of box or shield to keep the fiberglass out. Same as when we use Ohmite pots. Good luck! Kent Quote Link to comment Share on other sites More sharing options...
RoyC Posted January 28, 2021 Report Share Posted January 28, 2021 The person peddling the misinformation is also selling L-pads for use in other speaker brands. I have seen melted and burned original pots, but have never seen a heat damaged L-pad in an AR cabinet. I have also tested the controls he is selling. They work satisfactorily, but if knobs are not used with them, the shafts are too stiff to turn without a screwdriver. The seller also implies he has something to do with the manufacture of the replacement pots, which is false. They are sourced from China and purchased in quantity through Alibaba. L-pads were used in the AR-3a Limited, which was manufactured in the late 80's. When the 25 ohm parallel resistor is used to make the L-pad act more like the original AR control, power handling is increased. Roy Quote Link to comment Share on other sites More sharing options...
JKent Posted January 28, 2021 Report Share Posted January 28, 2021 hmmmm..... He also says they're made in the USA! Quote Link to comment Share on other sites More sharing options...
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