Class 5 head problem ?

[ready505]

Hello everybody. I'm new to this forum and unfortunately my first post is because of a problem I'm having with a Class 5 head.

I have ruined two Celestion Heritage G12H-30 55hz speakers. It seems that I'm melting the glue in the voice coils. I bought an Avatar 1x12 loaded with one of these speakers and while breaking it in over the period of about a week and a half it developed a kind of "charm bracelet" buzz. Dave at Avatar sent me a replacement speaker which I swapped out with the bad one. I let that speaker sit connected with the amp on and the volume turned up but nothing connected to the input. After about 45 minutes I plugged in my guitar, lowered the volume and started strumming some chords for 15 minutes. Then I raised the volume a little and continued strumming chords and within 10 minutes the second speaker started making the same sound. I called Dave and he seems to think it is the amp. He also called Celestion and they think it's the amp. I should add that I replaced the tubes with a NOS Brimar 4004 in V1, a NOS Mullard 4024 in V 2 and a NOS GE EL84 power tube. Also, I too have the problem with the volume knob not cutting the guitar totally and I am occasionally getting a pop turning the amp on and off.

I have been using Marshall for almost 40 years and had just about everything happen that can happen but nothing like this.

If anybody out there has any idea what might be happening I would greatly appreciate the help.

[exotl]

A 5 Watt amp roasting a 30 Watt Celestion doesn't sound realistic to me at all.

[ready505]

An update:

It's also happening with my VOX AC15HW loaded wth a VOX Blue and JMP-1H and Egnater Tweaker cab. I've tried swapping tubes, cables, picks, everything I can think of. I couldn't possibly done the same thing to three amps or four speakers. Is there a possibility that there is something going on with the electric service into my house? Something that the amps aren't filtering that's getting passed to the output? Everything else electrical seems to be working properly- TVs, stereo, computer. I'm totally lost here.

[Dave W]

Well, thats some scary stuff.

It cannot be your Class5 if it is happening to your other amps now.

Have you changed guitars? I know thats sounds stupid, but how could it be all the amps. I would think its something in your signal chain like a guitar or maybe your electrical outlet.

Are the speakers dead or just buzzing?

If you are using a correct speaker cable and tried another one too that should rule out the connection from amp to speaker.

Have you moved the amps to a different area of the house to try a different outlet?

It is normal for the Class5 to have a small amount of volume to the speaker even with the volume at zero, some other amps do this too. it also is not uncommon for an amp to make a pop at times when powering on-off in my experience.

Let us know what the cause is when you find out as this one has me confused!

[ready505]

It happens with both my Les Paul and Telecaster. I use Mogami guitar cords but I've tried all my cords. No change. I have Mogami speaker cables between the Marshall heads and the cabs but I swapped them out with the cheapie Marshall speaker cables and some Proco heavy duty speaker cables I have. No change. I mixed and matched the amps and speakers, except the VOX Blue, which is hardwired. No change. I tried different circuits in my house. No change. I haven't tried anywhere outside my house yet because neither of my neighbors are in town because of Sandy. By the way, this happened weeks before Sandy hit so I'm ruling out any post-storm electric utility work on my grid.

It's nice to know that the volume and pop things are OK.

Update!!! Before I finished the above and posted it...

I just tried a Smokey battery power practice amp that has 1/2 watt output and can actually power a speaker. It was loud enough to reach well past the volume level needed to create the noise and NO NOISE! I am reasonbly certain that it is nothing to to with my equipment but something in the electric in my house. But what?

[ready505]

Well, I've just finished going through the house and unplugging all transformers, battery back-ups, anything that draws power even when off, all outlet surge protectors, shutting off the pole and outside garage lights that use photocells. Nothing makes a difference- the sound is still there, no better, no worse. It must be something coming in from the street. Don't know how to check or who to call.

[Dave W]

Thats frustrating and stresfull. Hopefully you get some answers soon after the neighbors are back or maybe take it somewhere out of the neighborhood and try it.

[David Corrales]

Definitely strange... did you try going back to the stock tubes? I know it sounds crazy but maybe the old glass is misbehaving.

[ready505]

Hi David. Yes, while troubleshooting I put everything back to stock in all the amps. Unfortunately it didn't make a difference.

[ready505]

Update time. Took the Marshall heads, the Avatar and Tweaker cabs to Coupe Communications in Ambler, PA and we ran a few tests. We only tried the Tweaker cab with both heads and the sound was still there but it wasn't as pronounced and now seems more off axis (see below). The tech hooked the cab to a tone generator and swept the speaker from 60hz to well past audible using sine, sawtooth and square waves at about 15 watts and we didn't here the sound. Then he hooked up dummy loads and measured the output wattage. Suprisingly, the Class 5 maxed out at 26.2 watts with the volume at 11 o'clock and the rest of the way had no effect. The JMP-1H registered 3.2 watts at 10:30 and went none higher. They checked out the Furman gear and it was fine. They gave me a device to check for bad grounds in my electrical service as they are known to develop suddenly and could cause voice coil damage by passing AC through the amp tranny and out to the speaker.

When I got home I checked every outlet in my house and they tested good. Next, I hooked everything back up, fingers crossed, hoping that something, anything, had changed. Good news, same news, good news. Good- the Tweaker cab now seems a little more open sounding with a little nicer low end. Same- the sound is still there. Good- the sound is somewhat diminished in the Tweaker. I've been playing the hell out of the AC15/Blue and pushing the Avatar and Tweaker cabs to see if I can get them to fail. Funny thing is they don't sound any worse. It's like the voice coils (if that is the problem, or what's making the noise according to Celestion) were damaged as much as they're going to be. As I said above, the sound now seems more off axis when playing loud. If I stand to the side I hear it. If the speaker is directly in front and in my face I don't hear it. Don't know, my ears are tired. I'm tired. Gonna leave it alone for a few days. More food for thought.