EL84M Issues in Amp?

[cap217]

My RXES has sovtek el84M's installed. I rarely put it past 6 but today I did and I got a horrible screech-feedback, then the 1/2 amp fuse blew.

I put a new fuse in and the amps works but with the EL84M tubes it sounds great up to noon then it starts to fart out and cut in and out. If I go to 7+ screech and blown fuse.

I swapped the EL84M for another new set and same thing.

Then I put in the old GT EL84s and no issues of farting out or blown fuses. I also tried JJ tubes and no issues. But the amp gets muddy and doesnt sound that good past 6. And at lower volumes the EL84M's sound a lot better and fuller.

What is going on here? Is this a tube thing or does it sound like something else? I am thinking that the amp cant take EL84M tubes (that doesnt make sense to me) because other tubes work. Or there is an issue with the amp and I will just send it to Z for repair. I am trying to rule out simple things first.

I guess its possible that I have 2 bad sets of EL84Ms but I used them in a Kane Liverpool by his recommendation and got this same type of screech-feedback. He said 2 tubes were bad back then. Maybe there are quality issues with these.




Also, off topic but I have a Sovtek rectifier in there and swapped it for another Sovtek to rule out that. Then I tried to put a JJ in there and it wont push into the tube socket. I am pushing hard and working it back and forth and yes, its lined up properly. The Sovtek goes in perfectly.

[Stevem]

One or both of the tubes must be arcing at a certain level of drive signal/ current draw.
The JJs are a far better built and sounding tube all around and has it way over the Rusky when drivin hard not only in cleam mode so I would just stick with them and be done with it!

[cap217]

One or both of the tubes must be arcing at a certain level of drive signal/ current draw.
The JJs are a far better built and sounding tube all around and has it way over the Rusky when drivin hard not only in cleam mode so I would just stick with them and be done with it!

I was afraid of that. I bought 3 sets of the 84m tubes and they are all bad. Makes me mad.

[randalp3000]

about a year ago EH had a big sale on el84m's and I bought 10. I checked them on my Amplitrex and they all had very low current as well as other parameters.

sometimes you get what you pay for with tubes. I learned my lesson, maybe.

[cap217]

about a year ago EH had a big sale on el84m's and I bought 10. I checked them on my Amplitrex and they all had very low current as well as other parameters.

sometimes you get what you pay for with tubes. I learned my lesson, maybe.

Thats the thing. These are more money than standard EL84s and they werent on sale. Every set of these I have ever used (5 total) have been bad.

[billyz]

about a year ago EH had a big sale on el84m's and I bought 10. I checked them on my Amplitrex and they all had very low current as well as other parameters.

sometimes you get what you pay for with tubes. I learned my lesson, maybe.

The el84m is more like a 7189. If you test it as a standard el84 it might look weak. On my tv7 the difference is in the bias setting for each. 7189 bias at 10 , el84/6bq5 bias at 30.

[randalp3000]

about a year ago EH had a big sale on el84m's and I bought 10. I checked them on my Amplitrex and they all had very low current as well as other parameters.

sometimes you get what you pay for with tubes. I learned my lesson, maybe.

The el84m is more like a 7189. If you test it as a standard el84 it might look weak. On my tv7 the difference is in the bias setting for each. 7189 bias at 10 , el84/6bq5 bias at 30.

Thanks, good to know. I'll try that next time.

[cap217]

Tube Depot is going to replace 2 sets of the EL84Ms for me with Mullards (Ill pay the difference). I find it hard to believe that I got 4 sets of all bad EL84Ms but it might be the case.

I need to find a new EL84 now because I liked the bigger bottom and smoother/hi-fi mids on the M.

[Blackburn]

I just sent a quad back to TD because one of the four started redplating. I guess these tubes aren't as robust as advertised, and this thread seems to substantiate that.

[cap217]

I just sent a quad back to TD because one of the four started redplating. I guess these tubes aren't as robust as advertised, and this thread seems to substantiate that.

Glad its not just me. Well not glad that others tubes are failing but glad that I dont feel nuts for have all my sets be bad.

[cap217]

Is it possible that shops are not testing these properly?

[Structo]

A lot of tube sellers do not burn in the tubes before matching them.

So you, the lucky consumer, get to do it for them and find one tube that is 15ma lower than the other one.

I know at Doug's Tubes, they burn in tubes that will be matched before measuring them.

I have bought several sets of power tubes from Doug and they rarely drift more than 2-4ma of bias current

http://www.dougstubes.com/

[cap217]

A lot of tube sellers do not burn in the tubes before matching them.

So you, the lucky consumer, get to do it for them and find one tube that is 15ma lower than the other one.

I know at Doug's Tubes, they burn in tubes that will be matched before measuring them.

I have bought several sets of power tubes from Doug and they rarely drift more than 2-4ma of bias current

http://www.dougstubes.com/

Says he doesnt charge for low noise of microphonics testing but I dont see burn in. I do see others charging for all of those services though.