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Ampeg Cab Lighting Up

I am Soma

I am Soma

Jan 2, 2013
2,614
2,505
MN
#1
Good evening guys,
So I'm currently running a Fender Bassman 100T through an Ampeg SVT 410 HLF and have been doing so for about 4 months (switched to the Ampeg cab from a Fender 410 Neo). Great combo and have had no issues before tonight. The drummer noticed the cabinet lighting up whenever I really dug in. I was able to recreate whenever we got to a section of a song that was faster/heavier. In 20 years I've never heard/seen this so of course it freaked me out. I'll list my settings below. I'm hoping someone can tell me what is going on and how to fix it. My first thought is it was the tweeter, but I really have no idea why that crossed my mind. I'm thinking it's not a watts issue with the disparity between the what the amp can provide vs what the cab can handle, but again I'm def no tech.

Invalid Link Removed
Channel: Overdrive
Gain/Blend: 7
Channel Volume: 10
Bass: 5
Mids Freq/Volume: 8
Treble: 5
Master: 4 @ 100w setting

Ampeg SVT 410 HLF:
Tweeter 1/2 way up

Pedal Board:
EH Micro Pog:
Dry@10
Octave down @ 1/4
Octave up @3/4

EH Steel Leather:
Response and Level: 1/4

Other pedals I run that weren't being used during the cab lighting up:

TCE Shaker, Delay, Chorus, Flanger, Tuner, Reverb

EH Holy Grail

EH Super Ego

Seriously any advice/insight anyone can lend would be great as this kind of stuff keeps me up and worried!

Thanks,
Dustin
 
#4
I didn't think so - but maybe my mids approaching into treble territory. What are my options for protecting the cab? Would turning the tweeter off help? Re-EQ'ing? Or is the light coming on even mean it's hurting it at all? Thanks again for all your help!!!
 
#5
Try turning everything to 11. Seriously, have you pulled the plate on the back of the cab where the input jacks are located? Inside you will find what looks like an automotive tail light bulb. This is used in place of a fuse to protect the tweeter. The one I replaced was 24 volt. These are used for aviation purposes. I found some at an O'Reilly's Auto Parts store which was located close to an airport.

I discovered this when using a new markbass SD 1200. When I would slap or pop a string the amp would go into protect mode and shutdown. After a few minutes it would reset and I could turn it back on. The problem was that the bulb (fuse) was out in the cabinet and with the transients having no place to go the amp would shut down. It took several emails to markbass and some thinking to determine the problem.

If it lights up it's working but I would try to find some spares and tape them to the inside of the cabinet. I hope this helps and saves you some time.

Sleep well...
 
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#7
Holy I never knew about this kind of build before. Seriously thank you so much everyone. Most cabs I've owned never had a horn so never had this issue. I'll work on turning the horn down and tweaking the EQ and hopefully that solves the problem!
 
#9
I am Soma said:
Holy I never knew about this kind of build before. Seriously thank you so much everyone. Most cabs I've owned never had a horn so never had this issue. I'll work on turning the horn down and tweaking the EQ and hopefully that solves the problem!
Click to expand...
Don't worry about the bulb lighting up. That is not a problem. It's doing what it's supposed to. That's just the way they designed the circuit.
 
#11
Yep, ages ago I was cranking a fuzz patch on my (then new) Zoom 506 into one of my (then new) Ampeg 410 cabs, and noticed how it would light up when pushed even just a little. It has a standard "twist-in" socket, and I eventually replaced the original bulb something like an 1157 automotive bulb. I bought this cabinet new in early 1999.

20131009_124846_zpsac4cfbd4.jpg


I bought another one brand new in 2001, and have just recently pulled the rear panel for the first time. I noticed it has two smaller bulbs actually hot glued to the board... So much for an easy fix there!

20131009_125239_zpsde0ab045.jpg
 
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#12
wave rider said:
If I have the concept correct, there is a lamp (automotive?) in the crossover circuit to protect the tweeter. When you dig in, it lights up to use up the excess energy.

=wr=
Click to expand...
I've never heard of this that's crazy!! and why not have it so it can be easily seen by the bass player and is it even in the manual to keep people from freaking out when they see it?
 
#13
As I understood that video, he was saying if you're lighting up a lot, it's too much. Back off of some of the treble. Yes, the lights will protect your tweeter. - until they blow. The next thing to blow will be your tweeter.

Raf
 
#14
simplyamason said:
Try turning everything to 11. Seriously, have you pulled the plate on the back of the cab where the input jacks are located? Inside you will find what looks like an automotive tail light bulb. This is used in place of a fuse to protect the tweeter. The one I replaced was 24 volt. These are used for aviation purposes. I found some at an O'Reilly's Auto Parts store which was located close to an airport.

I discovered this when using a new markbass SD 1200. When I would slap or pop a string the amp would go into protect mode and shutdown. After a few minutes it would reset and I could turn it back on. The problem was that the bulb (fuse) was out in the cabinet and with the transients having no place to go the amp would shut down. It took several emails to markbass and some thinking to determine the problem.

If it lights up it's working but I would try to find some spares and tape them to the inside of the cabinet. I hope this helps and saves you some time.

Sleep well...
Click to expand...
i would want that bulb socket on the back outside where i could see it working and get at it quickly when/if it fails,and spares in close proximity...
 
#15
Raf Seibert said:
As I understood that video, he was saying if you're lighting up a lot, it's too much. Back off of some of the treble. Yes, the lights will protect your tweeter. - until they blow. The next thing to blow will be your tweeter.

Raf
Click to expand...
Actually, once the light blows, your tweeter quits working, or so I'm told, since I never have this problem because I never use them ;)
 
#16
Lamps are used quite a bit in the electrical/electronics industry for exactly that purpose, a simple and inexpensive current limiting device. I've seen them used on several equipment applications in my line of work (i'm an industrial electrician).

A simple lamp makes a great and inexpensive current limiting device because there's not much resistance when there's just a small amount of current. But once there's enough current to illuminate the bulb, the electrical resistance then starts to increase very rapidly due to the lamp element heating up.
 
#19
The bulbs do act as a fuse and if pushed hard enough will blow. That is why they call them fuse bulbs. So take care when you see it flashing.

The resistance of the bulb increases as current passes through it. When the bulb lights it is dissipating excessive energy as heat. A problem with them is that, relative to a spike, they can be slow to react. So they aren't perfect. Still better than nothing and they do a good job at protecting the horn most of the time.
 
#20
dogbone nailed it. When cold, the bulb has low resistance, passing signal easily. When it gets enough power to light up, the resistance goes up, cutting down the signal to the tweeter.

There are variations on this design. Some use automatically resetting PTC fuses. These look like small ceramic caps. some use combinations of the bulb and resetting fuse. The PTC alone turns the tweeter on and off. That's not ideal. Better designs will put a 2 ohm resistor and PTC fuse in series and then put the bulb in parallel with that. If the fuse opens, the bulb takes over, varying the output of the tweeter.

Your bulb lighting up is a good thing. If it were not there, the tweeter would have likely blown.
 

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