Electra dyne big issue with speakers blowing out

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Hi to all,

Am facing with possible big problem with my Electra Dyne 112. The needed inputs to approach this topic are:
1. Mesa boogie - Electra Dyne 112 110 V (i use a transformer to convert from 220 to 110 V for all the time i have the amp more than 6 years now)
2. Celection Black Shadow 90W 8 ohm speaker (stocked)
3. Celection AlNiCo Cream 90W 8 ohm speaker (custom purchase) surprised to measured at 6.7 ohms and i didn't put the amp switch to 4ohms as i used it on so many occasions as one spaker to 8ohm setting, yes this can increase the total W as P=U*I and I=U/R :(
4. 6l6 (new and used) and EL34 (new) power tubes , amp has bias selector
5. Amp has 4/8 ohm switch but this is not applicable to this test.

Problem No1
While doing a setup for a recording session (nothing out of the ordinary usage) i've experienced a sound being interrupted like a falty cable experience (on/off). This went on for few minutes and I don’t’ know why I suspected maybe it is the power tubes 6l6. As I have a mess boogie branded 6l6s I decided to switch them. No surprise at all the same problem persisted. However, I did noticed that when the signal was not being played through the speaker I heard from the amp (possibly from the tubes or I don’t know which part would be doing this), also when the signal reappeared on of the entirely new tubes were producing a blue flame (not very big one but enough to be noticed).
After few more minutes of testing the signal just stopped entirely, so I decided to call it a night as I was not going anywhere. At this point my Black Shadow speaker is in an external cabinet and I have in the combo installed Alnico Cream Celection 90W 8ohm, but not plugged in only was using the stock Black Shadow also 8ohms for the recording.
I called in a person that deals with amp repairs so not much but bring it in or check if the speaker is blown.
On the second return i tried testing with multimeter so no Ohms were produced and no response to batter test on the speaker so it has surely died.

Problem No2
I called in the guy again to tell him that it was the speaker and as I need to do recording I will use the Alnico Cream speaker but I wanted to make sure that I take some preventive measures so the same would not happen. He told me, turn on the amp, put the multimeter on the speaker connectors and without playing just check if the amp is sending DC voltage to the speaker. I’ve asked what would be acceptable tolerance if there is any kind of DC voltage, he said, as long as the DC voltage messured is in the small mV amounts. Test performed, all good only very small DC mV I measured, I also checked what happens when I set the multimeter on ohms, when amp was on on the speaker connectors the ohms were very close to 0 ohms. So taking the advice of the person with high experience, and confidence boosted form the no damaging Volts measured i produced to do a short playing test.
But, before I made all measures I made a poor choice to do another power tube swap as I also have branded Mesa boogie EL34s. Wanted to try them for recording to get a different tone. As the Electra Dyne offers a bias switched I made sure I put it on the EL34 setup (red led indicator is on). I tried the amp for few minutes and I was actually playing it on 90W starting from not so much loud to a loud setting but not pushing the max limits.
After 6-7 minutes of playing, the Cream Alnico speaker just went from 100% sound to 50% sound with some cracking notice. I stopped playing immediately, turned off the amp and tried a very simple test to gently push the speaker cone inwards. Yep, it produced the scratching noise and I new that the coil of the speaker is damaged but not entirely broken as it still produced a sound and a bit stiff flexibility.

The mistake I regret doing is the power tube swap from 6l6 to EL34 as i have no consistency now, as I have never played the Alnico Cream 90W speaker with those tubes. I did played it with 6l6 a lot, even pushing the amp a lot, never had i had problems in the past. If I had use the 6l6s I was going to be more sure that this is the AMPs fault. However, I might have blown this speaker by the 90W setting and simply using the EL34s that deliver a hotter signal as the end product might be more than 90W of power.
One last AMP test, I paired the electra dyne with an 18” Electro Voice 8Ohm 400W speaker to see if the AMP is still working. Tried it for 10 sec and I noticed that amp signal is ok, guitar sound and tone all fine and turned everything off, being afraid not to blow this 3rd speaker

The wrap up:
I have produced a damage of nearly 700$ worth of speakers and an AMP that possibly will burn another speaker with a big doubt to even take the Amp to the repair person (that has a lot of experience) as I simply told him everything on the fly and his conclusion after the second speaker died was, "well I don’t know what to think now"
Thanks for even reading this entire text, and also many many thanks for useful guidance.
 
stephen sawall said:
Blowing two speakers is unusual. Don't know what to think about this one.

Stephen thanks for replying, yeah it is very unusual and am so angry with my self to make actions that would lead to results that can't be narrowed down. Very amateur of me to introduced inconsistencies in changing the test environment to produce new outcomes. But this EL34 swap possible issue popped as a mental hygiene 2 days after the "lovely" experience
 
Don't feel too bad...we all make mistakes and learn. I've blown a few speakers and have had amp issues.

I had a tube red plate last week and take out a bias resistor.
 
So weird. To me, the crackling and volume fluctuation kind of smells like power tube failure.

Have you tried moving the voice coil manually by gently pushing on the cone? If the speaker is blown, the voice coil will rub and make noise
 
marjan.jovanovski said:
3. Celection AlNiCo Cream 90W 8 ohm speaker (custom purchase) surprised to measured at 6.7 ohms and i didn't put the amp switch to 4ohms as i used it on so many occasions as one spaker to 8ohm setting

It’s normal for an 8ohm speaker to measure between 5 and 7 ohm at idle.

A 4ohm speaker would measure between 2.5 and 3.5 ohm at idle.

Beyond that, I’m not sure why you’ve blown two speakers.
 
Do you have something in fx loop? The erratic cutting I’ve had most frequently have been caused by dirty fx loop connectors not making proper connecting while the loop is empty 🤔
 

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