I picked up my spkr from the tech. I took him your suggestions & he disregarded them, instead repl. 2 diodes & 1 resistor. I haven't plugged it in yet. I am going to continue on myself. I will gladly remove a tweeter to mail you. I believe you can send me a private mess. w/ your address. No level change w/ L-pad rotation. I am going to buy a low cost capacitance meter from parts express along w/ more caps and recheck. I have been suspecting the diaphragms suffer from old age. Can't tell if all tweeters have same output. Woofer is clearly louder. E-bay has an Isophon ST H 5/16 init appears very close dimensionally. I only mention this in passing. Thank You. civil6
I removed dia. tweeter panels. They are about 1 1/2 x 5 1/2 x 5/16 thick. A rear cover, spacer and the dia. itself is all there is to it. The dia. is left exposed, (ergo single ended) only protected by the grille fabric. No visible damage (tears, disintegration) to dia. It looks like alum. foil with appox. 5 longitudinal bevels of a very slight angle. All wiring solder joints are firm, very little oxid. @ some mounting tabs. It's so simple it looks infallible. The dia. are all dry. Are they supposed to be? Thanks to "you all" for the GREAT insight. I'm so excited I don't even want a beer!
2a tweeters removed
This is what the single ended tweeter panels look like. I put ohmeter probes across each one, could not get any reading. I set dial to each division; from 2k to 20m. Nothing. Any ideas? Thx, civil6. Disregard rt. photo.
This is what the single ended tweeter panels look like. I put ohmeter probes across each one, could not get any reading. I set dial to each division; from 2k to 20m. Nothing. Any ideas? Thx, civil6. Disregard rt. photo.
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Since the ESL panel is a capacitor, you should not get a resistance reading across the terminals. If you did that would indicate a shorted panel. Of course you already proved you didn’t have shorted panels because you measured ~300Vdc bias voltage with them wired up. You should, however, get a capacitance reading if you happen to have a meter than can measure it.
It is hard to understand exactly how the contact is made to the conductive metallic coating on the diaphragm. Can you measure resistance on the surface of the diaphragm when placing your meter probes 1/4” apart on the diaphragm? I know Philco put a coating over top of the conductive layer on the ESLs, so maybe these were built in a similar manner.
The ESL is made up two electrically isolated parts:
1) the diaphragm with a conductive layer stretched across
2) a curved perforated sheet metal surface.
An electrical connection needs to be made to each part.
As best I can tell, the riveted terminals are connections to the curved sheet metal surface under the diaphragm. The rivet also is used to attach the metal surface to the grey insulator plate. The diaphragm is wrapped around the curved metal surface and glued in place on the back side of the grey insulator plate. Then the whole assembly is placed inside the metal frame. The 4 slots on the back side of the metal frame appear to show what I think is supposed to be the connection to the conductive metal coating on the diaphragm.
I found a few more pics on ebay that appear to be the same as yours...
It is hard to understand exactly how the contact is made to the conductive metallic coating on the diaphragm. Can you measure resistance on the surface of the diaphragm when placing your meter probes 1/4” apart on the diaphragm? I know Philco put a coating over top of the conductive layer on the ESLs, so maybe these were built in a similar manner.
The ESL is made up two electrically isolated parts:
1) the diaphragm with a conductive layer stretched across
2) a curved perforated sheet metal surface.
An electrical connection needs to be made to each part.
As best I can tell, the riveted terminals are connections to the curved sheet metal surface under the diaphragm. The rivet also is used to attach the metal surface to the grey insulator plate. The diaphragm is wrapped around the curved metal surface and glued in place on the back side of the grey insulator plate. Then the whole assembly is placed inside the metal frame. The 4 slots on the back side of the metal frame appear to show what I think is supposed to be the connection to the conductive metal coating on the diaphragm.
I found a few more pics on ebay that appear to be the same as yours...
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The butterfly wings touch the curved perforated conductor. Only one wing is active. The red lead attaches to (1) of the wings on the other side of the grey plastic. The foil is wrapped over the perf. conductor, around and under its sides. There are two strips of adhesive securing the foil film. That is where the tear occurred. The foil may be salvageable.
Real Elec 2a tweeter repair...
I finally got a chance to look at the tweeters you sent. Your disassembly pics pretty much show how they are built. The curved perforated stator plate has 5 runs of #38 wire to space the diaphragm away from the stator. The two brass springs tension the diaphragm by pushing the stator upward. The electrical connection to the stator is made thru the springs to the two terminals riveted on the back side of the plastic plate.
When I received them, none of the tweeters had conductivity between the metalized coating on the diaphragm and the metal base plate that the black wire is hook to. The metalized coating was still conductive all around the assembly, it just wasn’t making an electrical connection with the metal base plate. Looking at how they were originally glued together, the contact with the metal based plate seems a bit iffy.
For the repair I decided to use VHB tape of the same thickness as the cardboard it was replacing. By leaving the inner portion of the VHB uncovered by diaphragm it can be used to attach the plastic plate to the metal base plate. This will also provide a distributed pressure along the length of diaphragm to ensure positive contact between the metalized coating and the metal base plate.
The diaphragm measured at 1/2mil (12 μ m) in thickness. A cheap readily available replacement is the metalized Mylar used as emergency blankets which you can pick up at most sporting goods stores. The VHB tape is available at any hardware store.
The repair went smoothly and tweeter is happily “tweeting” again.
I’ll post some response measurements later this week when I get some time.
I finally got a chance to look at the tweeters you sent. Your disassembly pics pretty much show how they are built. The curved perforated stator plate has 5 runs of #38 wire to space the diaphragm away from the stator. The two brass springs tension the diaphragm by pushing the stator upward. The electrical connection to the stator is made thru the springs to the two terminals riveted on the back side of the plastic plate.
When I received them, none of the tweeters had conductivity between the metalized coating on the diaphragm and the metal base plate that the black wire is hook to. The metalized coating was still conductive all around the assembly, it just wasn’t making an electrical connection with the metal base plate. Looking at how they were originally glued together, the contact with the metal based plate seems a bit iffy.
For the repair I decided to use VHB tape of the same thickness as the cardboard it was replacing. By leaving the inner portion of the VHB uncovered by diaphragm it can be used to attach the plastic plate to the metal base plate. This will also provide a distributed pressure along the length of diaphragm to ensure positive contact between the metalized coating and the metal base plate.
The diaphragm measured at 1/2mil (12 μ m) in thickness. A cheap readily available replacement is the metalized Mylar used as emergency blankets which you can pick up at most sporting goods stores. The VHB tape is available at any hardware store.
The repair went smoothly and tweeter is happily “tweeting” again.
I’ll post some response measurements later this week when I get some time.
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bolserst: once again, how is the film tension determined? Does the film tighten as you push down and on to the spring arm? Do you trim the repl. film same size as O.E. before installing? Yes, they were assembled with a price point in mind...simplistic beauty! Merci beaucoup! civil 6
Sorry I wasn't able to take any pics while attaching the film, but the process required two hands.
I trimmed the replacement film to the OEM height, be left a couple inches extra on the width.
First I attached one side of the film to a VHB tape strip, then with the stator centered on the springs I pulled the diaphragm over the stator and down the other side. I pulled down with enough tension for the stator to completely depress the springs, then I pressed the diaphragm to the other VHB tape strip and trimmed away the extra. After assembly, the springs push the stator upward to keep the diaphragm tension constant even if it stretches a little bit with age.
I bought the dia. material @ TARGET. I'm unclear on the tape choice. 3M 411 and 414 are consumer grade items...ACE has the 411. The VHB line of tapes is quite expansive. I have no idea where to start. Some VHB tapes are only sold by the case...any suggestions? Thanks, civil6
The 411 should be fine. You can get small rolls of either 411 or 414 at Home Depot.
You don't need much of it, so can buy the smallest roll to avoid expense...should be $5 - $8.
As requested, here are a couple more pics during the assembly process.
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Here is an overlay of measured response for the 4 tweeters.
Up to 14kHz they match surprisingly well considering the construction method.
They have been shipped back to civil6. Hopefully in the next week or so he can get them wired back in and report back on the sound.
Up to 14kHz they match surprisingly well considering the construction method.
They have been shipped back to civil6. Hopefully in the next week or so he can get them wired back in and report back on the sound.
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I just wired up the 4 ELS tweeters & connected to an amp. I'm way satisfied. They sound really fine. Sure, they are single ended...but I'm 64 & don't play as loud as I used to! The old ad from RS back in the day was spot on...you really do need at least 12 watts. I recommend them.
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