Large Advent possibly blown?

[JKent]

Thanks Doug

btw--I don't want to start a controversy about caps--everyone has their own opinion--but the Carli Mylar caps at Madisound are good IMHO and inexpensive. The 8uF is $1.95 and the 15uF is $3.40. And 15 is close enough to 16 (figure +/- 10% is OK). If you are compulsive you could wire a 1uF in parallel (0.60 ea) but it's not necessary.

Kent

[Doug G.]

Actually, yes, a good argument could be that Leo may want to hear their original sound before making any modifications. Thus, installing a 16uF cap. first and see how he likes it.

Doug

[Leo7504]

I thought Imade two posts but I think they got censured, Doug, I removed the cap in the picture you saw because I hought you had to have them out of the circuit to test impedence. There must be some law of physics that says you don't.

On the speaker in question, the only thing that shows any resistance is the resistor which measures 3 ohms. Everything else both caps and both inductors show 0.

I picked up a pair of 1974 OLA's on Saturday and they sound great. When playing next to my other OLA I noticed that the tweeter sounds veiled or muffled and not at all bright. When I pulled the bass to test the crossover components I found the yellow colored inductor and the bottom cap both at 0. Does this indicate these need to be replaced?

Yes Doug, you are right, I would try to restore to original, particularly with the new set which I plan on using in a stacked configuration as soon as I can restore them to original performance.

Any suggestions on glue to use to attach the new components to the crossover plate? Also, what to use for putty to make the cabinent airtight when I replace the bass speakers.

Thanks,

Leo

[Doug G.]

OK, now I understand re C2! :^)

Anyway, when you say some of the components show 0, do you mean that the display on the meter stays blank or do you mean that it actually shows "0"? If it stays blank, that means the component is open (like a broken wire). If the display shows, like 0.00, that means the component has no resistance or is shorted.

OK, so R1 is OK (3 ohms). The small inductors will not have a very high DCR (direct current resistance) but should not be absolutely zero. This would indicate that they are shorted. If L2, the inductor in parallel with the tweeter, is shorted, that would kill any output from the tweeter as it would short the signal to ground.

If L1 is shorted, it would not kill the tweeter since signal would still pass through it. The output would just not be correct for the switch setting.

If the caps are shorted, signal would still pass also but would be way too much low frequency content for the tweeter and would be bad for it.

No tweeter output has to be either L2 shorted or other components open.

I guess it's always possible that the switch has gone bad but it's not probable.

I guess you could just replace all of the components as it wouldn't cost that much. Advent used hot-melt glue to attach the components to the plate and you could use that or any glue like contact cement.

The usual "putty" to use for sealing the woofer back to the speaker board is called "Mortite" which is a brand name. It's handy because the roll is divided into strips and you can just pull one strip away from the roll and run it around the woofer surface where it meets the board. You can get it at Home Depot.

BTW, if your tweeter is measuring 4 ohms, that's too high. It should be around 2.5 ohms. It indicates that the tweeter may have been overheated by your son :^)

Doug

[Leo7504]

Doug,

OK. I've ordered replacement parts. Does the 4 ohm reading on the one tweeter mean that I should get a replacement? Pete said to mount the inductors as far apart as possible, does that mean more than the two inches that separate them currently?

Leo

[Doug G.]

OK great!

Yes, I would replace the tweeter because your current one probably will have low output.

They are on eBay all the time. Make sure you get one meant for the original Advent and not the smaller Advent. The magnets on the regular ones are 3" square and the smaller ones are 2.5" square.

2" should be plenty of space for the inductors.

Doug

[Pete B]

Thanks Doug

btw--I don't want to start a controversy about caps--everyone has their own opinion--but the Carli Mylar caps at Madisound are good IMHO and inexpensive. The 8uF is $1.95 and the 15uF is $3.40. And 15 is close enough to 16 (figure +/- 10% is OK). If you are compulsive you could wire a 1uF in parallel (0.60 ea) but it's not necessary.

Kent

Those are fine Kent, however Polys are better, they've gotten a bit expensive

for the Bennics. While I agree that 15uF is close enough, many people like to

match between right and left if it is their main system and a simple way to do

it is with higher tolerance parts. PE has 1% caps here:

http://www.parts-express.com/dayton-loudsp...precision-1.cfm

Meniscus has 3% here at a much more reasonable price, yet significantly better

than 10%:

http://meniscusaudio.com/capacitors-pulsex...-c-101_104.html

You can also find 2% resistors at PE.

[JKent]

Two thoughts: I've been advised that hot melt glue should not be used to fasten capacitors because the high heat can damage them. You could use a mechanical means, such as a cable tie, or try "Goop" or an RTV (silicone caulk and the like). Suggest you refer to the AR 3a Restoration Manual in the Library.

Another option instead of Mortite is "Duct Seal" sold in the electrical dept of hardware stores, Home Depot, etc. It is a brick of black stuff that you can roll in your hands like plasticene modeling clay to make a long thin snake to seal the drivers.

Kent

[Pete B]

Doug,

OK. I've ordered replacement parts. Does the 4 ohm reading on the one tweeter mean that I should get a replacement? Pete said to mount the inductors as far apart as possible, does that mean more than the two inches that separate them currently?

Leo

4 ohms on the tweeter is correct for the early LA as you can see from my

schmatic where I list the DC resistance for the drivers. The New LA tweeter runs

between 2 - 2.5 ohms.

What does the other one read?

Caps should be an open circuit, inductors ideally as close to zero as possible.

However, the small early LA inductors used VERY fine wire and the steel colored

one should measure about 2 ohms, not near zero. I also list the correct measured

values at my web page.

Not to offend, but are you good with a meter Leo? You need to have clean contacts

a good battery, it properly zeroed to get good low ohm readings, and a decent

meter of course.

Another thing, you mention a new pair, they could be the later revision in which

case you might want to rebuild this pair also as the later revision. The difference

is not that significant, and the newer revision offers better protection for the

tweeter.

[Pete B]

Two thoughts: I've been advised that hot melt glue should not be used to fasten capacitors because the high heat can damage them. You could use a mechanical means, such as a cable tie, or try "Goop" or an RTV (silicone caulk and the like). Suggest you refer to the AR 3a Restoration Manual in the Library.

Another option instead of Mortite is "Duct Seal" sold in the electrical dept of hardware stores, Home Depot, etc. It is a brick of black stuff that you can roll in your hands like plasticene modeling clay to make a long thin snake to seal the drivers.

Kent

Kent - most caps are rated for 85 deg C, some even 105 deg C, military types up to 125 deg C.

I really don't think that hot glue is an issue if you work fast and do not touch the hot metal

tip to the cap case. I've noticed much better quality hot glue these days that sticks better than

the old stuff. Use a good quality glue of this type.

Silicone glues release acetic acid, I would not use them:

http://yarchive.net/electr/silicone_sealan...rosiveness.html

I hear that Goop is also very good and safe if you want something in a tube.

[Leo7504]

Pete,

No offense taken, I changed the battery on the meter, which is an analog multimeter from Radio Shack that I got just for this purpose, I paid about $28 for it. It has an X1 scale to allow for a low reading. I zero the meter before each reading, and the tweeter reads 4 ohms. The other tweeter reads 1.5 ohms. Does this indicate possible damage?

My Advents show a Sept 1972 date. The ones I just acquired show a November 1974 date.

At this point I think I will update the crossover components and see what it soulds like. I will keep you posted.

Thanks,

Leo

[JKent]

Thanks Pete for the tip re silicone. I was going by info on p 16 of the AR3a manual

http://www.classicspeakerpages.net/library...-3a_full_pd.pdf

but better safe than sorry. There are other types of RTV, such as Phenoseal, which should be safe but take a while to cure. Mechanical fasteners are always good.

Leo: See p 19 of the AR3a book for discussion of Mortite, duct seal, etc.

Kent

[Pete B]

Pete,

No offense taken, I changed the battery on the meter, which is an analog multimeter from Radio Shack that I got just for this purpose, I paid about $28 for it. It has an X1 scale to allow for a low reading. I zero the meter before each reading, and the tweeter reads 4 ohms. The other tweeter reads 1.5 ohms. Does this indicate possible damage?

My Advents show a Sept 1972 date. The ones I just acquired show a November 1974 date.

At this point I think I will update the crossover components and see what it soulds like. I will keep you posted.

Thanks,

Leo

The 1.5 ohm tweeter is bad.

Probably excessive heat that destroyed the insulation between windings.

I believe that the 1974s are probably the later revision, you might pop them open to

have a look. The tweeter inductor will be a bar type if so.

I would then for sure rebuild your first pair with the later revision values.

I really prefer Mortite to reseal the woofer, it is what Advent used and is

available at Home Depot. Your 1974s should also be recaped, the caps are just well

past even their shelf life.

[Leo7504]

Will do, I will keep you updated on my progress.

Thanks Pete,

Doug,

for your advice.

Leo

[Leo7504]

Pete, Doug,

Got the parts in the mail today and when I got home from work I replaced all four caps and both inductors in each speaker. The caps were bought on line a couple of weeks (Dayton) ago and they were a 15 and a 1 wired together. The new inductors from Madison were significantly larger than the old. It was about midnight when I finished so I didn't have a chance to give them a critical test to see how they sounded. I did wire them in paralell with the top advents upside down and played what was on the turntable "Sunny Side of Heaven" Danny Kirwan old Fleetwood Mac.

Is there a post that suggests wiring a fuse when the speakers are stacked? I don't want anyone blowing these guys up now. Pete and Doug, you guys have been a great help in guiding me through this.

Leo

[Pete B]

Pete, Doug,

Got the parts in the mail today and when I got home from work I replaced all four caps and both inductors in each speaker. The caps were bought on line a couple of weeks (Dayton) ago and they were a 15 and a 1 wired together. The new inductors from Madison were significantly larger than the old. It was about midnight when I finished so I didn't have a chance to give them a critical test to see how they sounded. I did wire them in paralell with the top advents upside down and played what was on the turntable "Sunny Side of Heaven" Danny Kirwan old Fleetwood Mac.

Is there a post that suggests wiring a fuse when the speakers are stacked? I don't want anyone blowing these guys up now. Pete and Doug, you guys have been a great help in guiding me through this.

Leo

Thanks for checking back in, good to hear that they're working again!

Sounds like you kept them original with 16/16 caps and just the tweeter

inductor replaced?

[Doug G.]

Good deal that you got them going, Leo!

If you use the search function and use "fuse", you will get quite a few hits on this subject.

Here's a good one regarding stacked Advents and fusing them:

http://www.classicspeakerpages.net/IP.Boar...927&hl=fuse

Doug