tvickey Posted February 20, 2023 Share Posted February 20, 2023 Hi All, So my new band just played our debut show on Saturday, and I took one of my GK 410 RBH cabs. These things handle 800 Watts 8 Ohms... We were up first at the show, I didn't notice anything unusual while I was playing through our set. Signal was going into the cab via the 1/4 socket rather than the SpeakOn. The bassists in the bands that came after us all used my cab, most of them with their own heads. I was around and helped connect things, and we were always using my speaker cable which is really high quality (nice Designacable one with Neutrik jacks). During the performance of the very last band, I noticed that something was glowing periodically in the upper left side of the rear of the cab. There was a white / yellowish glow that looked to me like it was coming from sparks. The glow was so bright, that it even shined through the paper on the speaker cones on the left of the cab. Everything continued to sound fine... performance went on and the cab never caught fire or anything. 😂 Has anyone seen this happen before? I'll have to pull out a speaker or two and see what is going on back there... I also wonder if using the 1/4" jack rather than the SpeakOn connector had something to do with it. I have two of these 410 cabs, have driven them really hard in the past, but never experienced any issues. BUT on all other occasions I was using the SpeakOn socket. Quote Link to comment Share on other sites More sharing options...
AndyTravis Posted February 20, 2023 Share Posted February 20, 2023 Some PA Speakers (and possibly cabs?) have a bulb in them as a circuit breaker to protect the speakers… I’m sure peavey did this. I might be wrong…it was a long time ago and I’ve met many beers since then… if I’ve imagined this - I’m very sorry. God…I answered that really quickly and now I’m doubting myself. now I’m trapped in an internal monologue… 3 1 1 Quote Link to comment Share on other sites More sharing options...
Acebassmusic Posted February 20, 2023 Share Posted February 20, 2023 Andy, you are correct 👍 In my old SWR cabs they had bulbs as fuses to protect the tweeter / horn from over enthusiasm 😁 2 Quote Link to comment Share on other sites More sharing options...
tvickey Posted February 20, 2023 Author Share Posted February 20, 2023 Actually @AndyTravis, I think you might be right. I don't know the inner workings of these GK cabs, but just googling around a bit now folks mention light bulbs acting as a current limiting device in a lot of cab circuits (as simple fuses could just blow). I was reasonably sure that I had driven these really hard in the past, but perhaps I just never looked closely enough to notice the glow. 1 Quote Link to comment Share on other sites More sharing options...
AndyTravis Posted February 20, 2023 Share Posted February 20, 2023 Ah good. I’ve just counted my marbles…and they’re all present. If I might push my luck - I’d suggest the bulb might be housed in or around the back plate (with all the input gubbins). if I’m right there - I will be pleasantly chuffed with myself. 1 Quote Link to comment Share on other sites More sharing options...
tvickey Posted February 20, 2023 Author Share Posted February 20, 2023 3 minutes ago, AndyTravis said: If I might push my luck - I’d suggest the bulb might be housed in or around the back plate (with all the input gubbins). Yeah, that is all situated at the back-left on the RBH cabs... exactly where I saw the glow. 1 Quote Link to comment Share on other sites More sharing options...
AndyTravis Posted February 20, 2023 Share Posted February 20, 2023 Well, I’ll go and get myself a chufty badge. been a while… A broken clock is right twice a day etc. 4 Quote Link to comment Share on other sites More sharing options...
King Tut Posted February 20, 2023 Share Posted February 20, 2023 Eden cabs have the lightbulb protection as well. I remember going into Halfords to replace a duff one! 2 Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted February 20, 2023 Share Posted February 20, 2023 These are really common, it's a really simple solution to protecting the speakers, mainly the tweeters. The bulb has a very low resistance when cold but as the current increases it heats up and the resistance rises reducing the current to the tweeter. In the quieter sections it cools down and full power is restored. 3 2 Quote Link to comment Share on other sites More sharing options...
Woodinblack Posted February 20, 2023 Share Posted February 20, 2023 46 minutes ago, tvickey said: I was reasonably sure that I had driven these really hard in the past, but perhaps I just never looked closely enough to notice the glow. I would imagine that every time you have driven the cab hard you haven't been facing it? 2 Quote Link to comment Share on other sites More sharing options...
AndyTravis Posted February 20, 2023 Share Posted February 20, 2023 3 minutes ago, Woodinblack said: I would imagine that every time you have driven the cab hard you haven't been facing it? Yeah - I meant to say that, but I’d excelled myself by remembering something 1 1 Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted February 21, 2023 Share Posted February 21, 2023 4 hours ago, Phil Starr said: These are really common, it's a really simple solution to protecting the speakers, mainly the tweeters. The bulb has a very low resistance when cold but as the current increases it heats up and the resistance rises reducing the current to the tweeter. In the quieter sections it cools down and full power is restored. Correct. In effect they work like a compressor, taming transient peaks that otherwise might cause the tweeter to fail. In extreme cases of overpowering they'll blow, turning them into fuses, although that's not their intended purpose. Those extreme cases are usually the result of using distortion effects, which increase the high frequency power content well beyond what most bulbs or tweeters can handle. 2 1 Quote Link to comment Share on other sites More sharing options...
tvickey Posted February 21, 2023 Author Share Posted February 21, 2023 6 hours ago, Woodinblack said: I would imagine that every time you have driven the cab hard you haven't been facing it? Yes, of course you're right. It was also not always as dark as the venue on Saturday. Quote Link to comment Share on other sites More sharing options...
Bunion Posted February 21, 2023 Share Posted February 21, 2023 They’re in ampeg cabs too the stop the horn from blowing, my old 210 is a normal car tail light but I think they’ve updated them now to something more fancy 😄 1 Quote Link to comment Share on other sites More sharing options...
KingBollock Posted February 21, 2023 Share Posted February 21, 2023 I remember when I was a kid an had started mucking about with electronics, I had an idea… I had been given a pair of 1x12 speaker cabs. They were huge, something like 24”x18”x18”. I assume they were PA cabs or something, they weighed a lot, too. Anyway. Each had a port along the front bottom (haha!) of the cab, and I had the bright idea (pun totally intended!) of wiring a painted (by me) car light bulb in series with the speaker. The idea being to give me a kind of disco light effect shining from the port. Surprisingly it worked! But I had no idea, at the time, that I was actually making the cabs better! (Although, they didn’t actually have tweeters). 1 2 Quote Link to comment Share on other sites More sharing options...
casapete Posted February 21, 2023 Share Posted February 21, 2023 Years ago I was playing in a resident band at a large cabaret venue. Whilst playing, a member of the audience tried to catch my attention, and thinking he was a drunk wanting a request I ignored him. He got more animated so I bent down to hear him shout ‘your PA cabs are on fire’ !! Turned out the Ohm cabinets had the bulbs fitted and were glowing a lot. 2 Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted February 21, 2023 Share Posted February 21, 2023 6 hours ago, Bunion said: They’re in ampeg cabs too the stop the horn from blowing, my old 210 is a normal car tail light but I think they’ve updated them now to something more fancy 😄 They've been using 24v aircraft bulbs for quite some time. 1 Quote Link to comment Share on other sites More sharing options...
ahpook Posted February 21, 2023 Share Posted February 21, 2023 Sounds like light overdrive to me 1 Quote Link to comment Share on other sites More sharing options...
Woodinblack Posted February 21, 2023 Share Posted February 21, 2023 Good oportunity here to improve things. You remember those fibre optic lights that were all the rage in the 70s? Well, they just had one light, a disk with lots of colours that just slowly spun and a group of fibre optic elements. If you can find one of those in a charity shop, take the disk out and fit that to your cab - so if you play hard enough you get a colour light show! 1 Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted February 23, 2023 Share Posted February 23, 2023 (edited) On 21/02/2023 at 01:01, Bunion said: They’re in ampeg cabs too the stop the horn from blowing, my old 210 is a normal car tail light but I think they’ve updated them now to something more fancy 😄 Probably something like a self resetting Polyswitch which are now used in my Acme cabinets replacing the lamp. Edited February 23, 2023 by BassmanPaul Quote Link to comment Share on other sites More sharing options...
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