I have a pair of vintage Ohm Walsh 3 speakers which the bass dropped out on. Took apart and found a blown filament lamp/fuse, NOT on the tweeter circuit as is typical on many speakers (though it had them there as well) but on the bass/woofer side. Contacted Ohm company but John Strombeen provided terrible customer support and basically refused to answer any questions I had regarding this lamp and would only resolve the issue by me shipping both cabs back to them and paying a ridiculous service fee, when all I need is a replacement lamp. Poorest customer service I have ever experienced from a stereo/music company but I digress...
The circuit, on the woofer side, post crossover, is basically a lamp (burn out - first picture attached) with a 14uf capacitor in parallel, followed by another larger filament lamp (second pic attached) which then connects to the woofer. The first (burnt out) lamp is the same filament size lamp that is used on the tweeter as well. From what I've gathered, these types of bulbs have a 0 resistance at rest, but as they heat up, their resistance goes up. So I'm thinking the parallel cap offers a method of bleeding off the lows, if the power gets too high. The state it's in now , with the lamp blown, there's an infinite resistance of course through the lamp. So 100% of the signal goes through the cap, thus acts as a high pass filter now and the cause of the loss of lows. But in normal use, low volume with a good lamp, Most of the signal goes around that cap, through the limiter lamp. lamp heats up as volume increases and I'm guessing as that bulb resistance rises, more signal runs through the cap vs the lamp, thus bleeding off the lows to protect the speaker. The second series (larger) lamp I assume just provides pure limiting, though I'm not clear of the design purpose, since the first lamp most definitely will blow before the second one ever does.
The cabs are rated 200 watt, 8 ohms (both woofer and tweeter are 8 ohms each) If I did my math correct that yields roughly 40V (sqrt(200 watts x 8 ohms)) which yields 5 amps (watts/volts), at full power.
Not clear if the second larger bulb really is a 5 amp one or not, or if both bulbs in series need to total to 5 amps. I've only found two bulbs of this type (festoon double ended) online of any substantial rating (parts express, amazon, ebay etc. One is clearly rated 12.8v 2.1a. The other is a Eminence PX:BULB which is a soldered pair. Can't find any specific rating info on that - it only states "provides smooth 3:1 analog compression during input overload conditions over 250 watts RMS" so i assume a Single bulb pulled off the pair does that to 125 watts.
Thoughts/Advice?
The circuit, on the woofer side, post crossover, is basically a lamp (burn out - first picture attached) with a 14uf capacitor in parallel, followed by another larger filament lamp (second pic attached) which then connects to the woofer. The first (burnt out) lamp is the same filament size lamp that is used on the tweeter as well. From what I've gathered, these types of bulbs have a 0 resistance at rest, but as they heat up, their resistance goes up. So I'm thinking the parallel cap offers a method of bleeding off the lows, if the power gets too high. The state it's in now , with the lamp blown, there's an infinite resistance of course through the lamp. So 100% of the signal goes through the cap, thus acts as a high pass filter now and the cause of the loss of lows. But in normal use, low volume with a good lamp, Most of the signal goes around that cap, through the limiter lamp. lamp heats up as volume increases and I'm guessing as that bulb resistance rises, more signal runs through the cap vs the lamp, thus bleeding off the lows to protect the speaker. The second series (larger) lamp I assume just provides pure limiting, though I'm not clear of the design purpose, since the first lamp most definitely will blow before the second one ever does.
The cabs are rated 200 watt, 8 ohms (both woofer and tweeter are 8 ohms each) If I did my math correct that yields roughly 40V (sqrt(200 watts x 8 ohms)) which yields 5 amps (watts/volts), at full power.
Not clear if the second larger bulb really is a 5 amp one or not, or if both bulbs in series need to total to 5 amps. I've only found two bulbs of this type (festoon double ended) online of any substantial rating (parts express, amazon, ebay etc. One is clearly rated 12.8v 2.1a. The other is a Eminence PX:BULB which is a soldered pair. Can't find any specific rating info on that - it only states "provides smooth 3:1 analog compression during input overload conditions over 250 watts RMS" so i assume a Single bulb pulled off the pair does that to 125 watts.
Thoughts/Advice?
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