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oldsoundz
11-25-2008, 11:09 AM
So I recently acquired a pair of Summits that needed work. They need foam/maybe cones. Having another pair on hand I swapped the woofers out and found the 077s were not working.:(

After pulling one of the tweeters I found that it was working properly.:blink:

So on further looking I found that something has somehow fried the hf/brilliance pot on at least one speaker. The back cap was off of the pot, laying inside, and shows signs of FIRE. I took a pic of the inside to share with the group.

Now I need to know how is the best way to correct this as one of the screws holding the pots is blocked by the foilcal. Don't want to screw it up.

Suggestion? Thought? And most of all, what the _____ Happened?

spkrman57
11-25-2008, 11:27 AM
Definitely much more wattage into that L-pad than is needed for tweeter duty!!!:banghead:

Hair dryer heat should lift the foilcal nicely from the front. Go nice and slow and don't force it.

Good thing you got a chance to resuce them and I'm sure they will sing real pretty when your done!

Ron

Hoerninger
11-25-2008, 11:29 AM
Party!
Weak amp and full power - fortunately it was the pot and not the tweeter!
As I do not like pots in a speaker I would replace the pot by a voltage devider. Some work is needed of course.
___________
Peter

grumpy
11-25-2008, 02:31 PM
Concur w/ Peter... If you prefer to not mess up the foilcal, wire up an 8-ohm L-pad in
place of the burned out unit (without removing the old one... just desolder/disconnect
the wires and attach them to the new one).

Find the setting you prefer.

Measure the resistances required for the divider, after taking the new/good L-pad
back out of the circuit.

Then wire up the two resistors matching the measured values from the good L-pad
and leave them inside (hoping 10watt-rated resistors would be sufficient).

For reference:

http://www.audioheritage.org/vbulletin/showpost.php?p=215410&postcount=7

oldsoundz
11-26-2008, 01:18 PM
I think I will be trying the hairdryer trick as I want to keep them as close to original as possible.

Thanks for the input fellas.

Chris

oznob
11-26-2008, 04:45 PM
http://audioheritage.org/vbulletin/showthread.php?t=5918&highlight=foilcal+removal

Here's an old thread that reinforces Ron's advise. The key is to go SLOW. I would recommend a heat gun if one is available. Good luck!

Mark

JBLRaiser
11-26-2008, 05:26 PM
http://audioheritage.org/vbulletin/showthread.php?t=5918&highlight=foilcal+removal

Here's an old thread that reinforces Ron's advise. The key is to go SLOW. I would recommend a heat gun if one is available. Good luck!

Mark


to keep it moving swiftly back and forth across the foilcal while working the thin, flexible 2-3" putty knife under it. The heatgun will bubble anything with a painted surface if not kept moving. With the hair dryer, you won't have that problem, but may take much longer to soften the cement. Once it reaches the proper temperature, the blade will slide under effortlessly.

mech986
11-26-2008, 05:48 PM
I swapped the woofers out and found the 077s were not working.:(

After pulling one of the tweeters I found that it was working properly.:blink:

And most of all, what the _____ Happened?

Hi Chris,

Always better to find out your 077 is working when you thought it was dead!!

Likely clipping or HiFrequency oscillation probably fried the L-pad. A similar problem occurs with the BBC LS3/5a if the speaker is fed signal from a RTR tape machine in full rewind with audio on. Can really put a hot signal into the UHF.

Use the hair dryer - you don't really want to have that dead carcass L-pad in there.

Regards,

Bart

oldsoundz
12-08-2008, 10:46 PM
So where do I find a replacement? Were there any lesser/more common networks that used the same pot? Or is it still available for some strange reason?

mech986
12-09-2008, 01:12 AM
http://www.jblproservice.com/pdf/Network%20Schematics/3133%20Network.pdf

http://manuals.harman.com/JBL/HOM/Technical%20Sheet/L300%20Summit%20ts.pdf

The 3133 / L300 equivalent schematics lists the L-pad as an 8 ohm 5 watt unit, part number 10285. The part number does not match up to any available L-pad through JBL Pro at present.

Aside from getting them used from another JBL part, IIRC, most advocate using Parts Express or equivalent part like this one:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=260-250

which is rated at 15 watts and has a 1 inch long shaft. Problem may be though adapting the knob to fit the shaft for the oem look. Also, seeing as you have limited space next to the mid L-pad, you'll probably want to measure carefully to see if it will fit.

Checking the other commonly available crossover/L-pads, it appears the 10285 unit is available scavenged from crossover in the 4311 and 4312 series, both using them for the tweeter and mids. That means the L-pad is likely the same on the L100 series too, which may be much more commonly parted.

http://www.jblproservice.com/pdf/Studio%20Monitor%20Series/4312LR.pdf

http://www.jblproservice.com/pdf/Studio%20Monitor%20Series/4311B.pdf

Also found in the L110, L150, L166, L19/4301, L16/26/36, L65 just to name a few. In short, should be able to find a good used one pretty easily if you have any access to parted crossovers and L-pads by JBL.

Hope that helps, good luck!

Bart

PS, found a couple of L65 crossovers with 2 L-pads each which went for $10 bux each on flea-bay so pretty easy to find a replacement for pretty cheap.

oldsoundz
12-09-2008, 08:35 AM
Thanks Bart

I have a set of trashed L36 that I have been unwilling to part with. :bouncy:This must be the reason I held on to them.

I will update the thread

Chris

oldsoundz
12-09-2008, 10:50 AM
Can you help me verify for sure this part will work?

My 36's yielded these...

I am assuming the brilliance pot, but I want to be certain. Thanks

Brilliance pot says:

CAT 40H
8ohm 50db
7601
Japan

Presence Pot says:

CAT 40H
8ohm 50db
1975-12
Japan

mech986
12-10-2008, 11:16 AM
Hi Oldsoundz,

Although not the same numbered, I'll go out on a limb and suggest that these are probably some OEM replacements when the inventory was low or costs were an issue. If both of the crossovers have all 4 the same, probably they were all subbed at the time of manufacture. If they are dimensionally ok, I'd probably give them a try, they're not pulling a ton of power.

However, if you really want the OEM part with number, you may have to continue your search.

Regards,

Bart

mech986
02-10-2009, 11:02 AM
Hi oldsoundz,

Did you ever sort out the 10285 L-pad issue? I keep seeing lots of them in L19, and 70's L series HF and UHF applications, among others. The crossovers are popping up fairly frequently so for OEM replacement, they're out there.

Bart

Got any pics of how those L300's ended up?

oldsoundz
02-10-2009, 12:32 PM
Hi oldsoundz,

Did you ever sort out the 10285 L-pad issue? I keep seeing lots of them in L19, and 70's L series HF and UHF applications, among others. The crossovers are popping up fairly frequently so for OEM replacement, they're out there.

Bart

Got any pics of how those L300's ended up?

Hey Bart

I have decided what I am using. I have it in stock:blink:

However, no progress yet as I am none to anxious to tackle the foilcal. I have been informed on how to do it, but still apprehensive.

Maybe this will start a fire burning again.

Hope you are doing well!

Chris