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Replacement drivers for old PA system
Replacement drivers for old PA system
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Old 28th October 2017, 11:18 PM   #1
Sorfak is offline Sorfak  Belgium
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Cool Replacement drivers for old PA system

Not sure if this is the right forum, but today I've been repairing an old PA speaker system (Novanex professional powertwin pl250) and need some help on choosing replacement components.

Some information about the system:
- There are two amplifiers: one for the left channel, one for right
- Each amplifier drives 2 woofers and 2 piezo horns.
- Woofers: Philips AD12100/HP4 12" 4Ohm (rated 0.04-12 kHz)
- Tweeters: Motorola/Peavey 15E83386 J03 (likely 4-27 kHz)
- All drivers on one side are wired parallel
- No crossover was used
- Everything mounted in one large case

I've managed to restore most of the system (I had to repair the tinsel leads on 3 of the woofers) but one of the 4 tweeters seems to be broken.

As it's very hard to find one of these tweeters for sale I was wondering if it's possible to swap out the broken tweeter with a similar one?
Do I just look for a tweeter with the same frequency range and similar impedance? Or just leave the system as is? It plays fine now but it'd be cool to repair it completely.

Same problem with the woofers. I've managed to get all of them playing again but the tinsel wire repair probably won't last very long so I'm also looking for replacements as well. Any tips/recommendations?

Thanks for the help,
Sorfak
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Old 29th October 2017, 12:20 AM   #2
conanski is offline conanski  Canada
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Do you really just want to put it back the way it was? Those piezos are super tweeters really.. they got no business operating at anything below 8-10khz. The original Motorolas were good at that though... the later replacements not so much, but given that info that leaves a sizeable hole in the mids to fill in with something... if you are buying drivers anyway. Lots of possibilities here including a using an 8-12" fullrange driver with whizzer cone or an actual closed back mid driver, and a crossover to make all this cooperate. Or you could stick with a 2 way design and substitute a proper compression driver and horn.. some enclosure mods necessary. I understand if this is a shoe string budget type of thing and you're not going to spend any more money than absolutely necessary, but given how cheap it is to buy a multi kilowatt power amp these days I fear these things will just get blown up again very quickly if you just put them back as they were found.

Last edited by conanski; 29th October 2017 at 12:23 AM.
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Old 29th October 2017, 02:27 AM   #3
nigelwright7557 is offline nigelwright7557  United Kingdom
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The Fane 12-250-TC is good full range speaker.
Go's up to 17KHz.
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Old 29th October 2017, 12:08 PM   #4
Sorfak is offline Sorfak  Belgium
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I'd like to keep the system a 2-way. And you're right, my budget is limited.
Say I want to replace
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Old 29th October 2017, 12:22 PM   #5
Sorfak is offline Sorfak  Belgium
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Quote:
Originally Posted by conanski View Post
Those piezos are super tweeters really.. they got no business operating at anything below 8-10khz. The original Motorolas were good at that though... the later replacements not so much, but given that info that leaves a sizeable hole in the mids to fill in with something...
Are you saying that if I swap out the broken horn with a new one ( for example Piezo Tweeter : Peavey.com) that I should add a filter to block out frequencies under 8-10 kHz?
But that would leave a gap in the mids?
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Old 29th October 2017, 01:57 PM   #6
JMFahey is offline JMFahey  Argentina
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Just thinking aloud:
1) that system is quite old.

2) those Philips speakers only stand 25W RMS each, fine in the 70īs, very little today.

3) are you sure they are 4 ohms each and wired in parallel?
If so, each cabinet would be 2 ohms total , very unusual and 99% amps out there canīt drive them.
**Maybe** they are wired in series in each cabinet, which would then be very reasonable 8 ohms each, cabinet stands 50W RMS and *may* be used with a *clean* amplifier up to 80 or 100W per channel, if always clean (as in a PA system in a Church); will last seconds under Rock/DJ use.

4) of course, if you also have the original Novanex amplifier driving it, speakers and amplifier "should" be well matched to each other.

5) I find quite worrying that you had problems with the tinsel wires, that makes me think about corrosion (humid environment?) in those 40 y.o. speakers; if so they will fail again quickly.
I would definitely try to buy 50cm or 1 meter (the minimum amount they will sell you) of speaker tinsel wire and carefully replace all 8.
Those speakers are excellent, just donīt stand high power by modern standards.

6) the tweeter is just "a plastic piezo tweeter", the brand and model which was available way back then; just use one of the modern generic ones.

7) IF you will replace the 12" speakers with modern ones, then what you have today is just a couple nice empty wooden boxes ... what will you drive them with?
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Old 29th October 2017, 02:43 PM   #7
Sorfak is offline Sorfak  Belgium
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Hey guys, thanks for the replies!

Quote:
Originally Posted by JMFahey View Post
2) those Philips speakers only stand 25W RMS each, fine in the 70īs, very little today.
I'm pretty sure those are rated at 50W max as it's the high power version (HP) of the ad12100 (I found an old Philips Catalog online with some specs)

Quote:
Originally Posted by JMFahey View Post
3) are you sure they are 4 ohms each and wired in parallel?
If so, each cabinet would be 2 ohms total , very unusual and 99% amps out there canīt drive them.
**Maybe** they are wired in series in each cabinet, which would then be very reasonable 8 ohms each, cabinet stands 50W RMS and *may* be used with a *clean* amplifier up to 80 or 100W per channel, if always clean (as in a PA system in a Church); will last seconds under Rock/DJ use.
Yes I'm 100% sure that they're wired in parallel and that they're 4 Ohms. I can say this because when we tested the system before the repairs, only one of the woofers was playing (the tinsel wires were damaged in the other three). This wouldn't be possible if it were a series arrangement.
Quote:
Originally Posted by JMFahey View Post
4) of course, if you also have the original Novanex amplifier driving it, speakers and amplifier "should" be well matched to each other.
Yeah we're still driving the speakers with the two original novanex amplifiers (which still work perfectly). I guess they're custom built for this speaker system? I'll see if I can obtain some more information about this system from Novanex (they're still in business)
Quote:
Originally Posted by JMFahey View Post
5) I find quite worrying that you had problems with the tinsel wires, that makes me think about corrosion (humid environment?) in those 40 y.o. speakers; if so they will fail again quickly.
I would definitely try to buy 50cm or 1 meter (the minimum amount they will sell you) of speaker tinsel wire and carefully replace all 8.
Those speakers are excellent, just donīt stand high power by modern standards.
While there was corrosion on the speaker terminals the tinsel wires don't seem te be affected. In three of the woofers, the tinsel wires were damaged in the exact same spot: always the right wire, at the point where the wire leaves the cone. The wire on the right seemed to always depart from the cone at almost a 90° angle which puts alot of unnecessary stress on it when the cone moves.
And you're right, these speakers are excellent. We're at least the third owner and this thing has taken alot of abuse over the years. Apart from the broken tweeter it's playing fine again (it's quite loud actually; Novanex put a warning note on the back: "Sound level may exceed 120 dB")
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