1987x with 3 month old eh 6ca7s bias 10ma apart

Minegoto11

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I put a new matched pair of EH 6ca7s in a 1987x that bandmates called the beast, (new preamp tubes as well) after it sat for a few years. The bias was set at 37ma with no issues and the beast was back! I had all the pots changed a few weeks later and the bias was checked, all good... I ran a gt8 with the 4cm and started "tone chasing". Something was off, but anyone who has a gt-8 knows there's a lot of annoying "tweaking". I'd get the tone close and the next day decide I wasn't happy and start over. It went down hill everytime I got close to what I want so I started thinking Im over doing it..... Last night I resert the gt8 and started from scratch.. Bam!!! sounded amazing, and went to bed happy.... Came home today and it was muddy and noisy, I checked the bias and 1 tube is at 31, tbe other at 42. swapped them and Its the same.... any suggestions?
 

79JMP100

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I put a new matched pair of EH 6ca7s in a 1987x that bandmates called the beast, (new preamp tubes as well) after it sat for a few years. The bias was set at 37ma with no issues and the beast was back! I had all the pots changed a few weeks later and the bias was checked, all good... I ran a gt8 with the 4cm and started "tone chasing". Something was off, but anyone who has a gt-8 knows there's a lot of annoying "tweaking". I'd get the tone close and the next day decide I wasn't happy and start over. It went down hill everytime I got close to what I want so I started thinking Im over doing it..... Last night I resert the gt8 and started from scratch.. Bam!!! sounded amazing, and went to bed happy.... Came home today and it was muddy and noisy, I checked the bias and 1 tube is at 31, tbe other at 42. swapped them and Its the same.... any suggestions?
If you swap the 6CA7's between their two sockets, and the original tube that read 42 still reads 42 in the new socket position- your tubes have simply drifted out of match. It happens, particularly if whoever you bought them from didn't burn them in before matching.
...A lot of places are now charging extra if you want your tubes burned in before they match them, which is completely ridiculous. Burn-in is *essential* to matching tubes, so any vendor who skips that process, or charges extra for it- should be avoided. Tubes need to be ran under realistic voltages until they stabilize, BEFORE testing for the numbers used to match up sets, which should consist of both current draw and transconductance. Unfortunately, there are plenty of vendors out there who either don't know how to do it right, don't care, or don't want to spend the time required. When my company was selling a lot of glass, we did it right, and had the electric bills to prove it...
 

Minegoto11

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Don't buy tubes from Electro Harmonix next time. :D
Yea I bought them after a friend recommended them and saw a few positive reviews .... Nobodys fault but my own for not looking into the company and checking for myself. After a little research I found they're rebranded garbage . A local shop has a couple matched pairs of el34s in stock, since tubes are in short supply Im gonna buy'em all lol...
 

Moony

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After a little research I found they're rebranded garbage

Even if I don't like them very much soundwise, they should work properly without the bias running away that much (though a certain bias drift with new tubes is normal).
I don't think they are "rebranded", they are made in the same factory like the new current production Tung Sol, Mullard, Svetlana and Sovtek tubes.
Of course I don't know if there's something wrong with your amp itself or if it's really the tubes.

I like the JJ EL34IIs. These were used by Marshall, too (with their label put on the tubes).
If you like more high mids and less bottom end, you could also try the Tung Sol EL34.
 

Minegoto11

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If you swap the 6CA7's between their two sockets, and the original tube that read 42 still reads 42 in the new socket position- your tubes have simply drifted out of match. It happens, particularly if whoever you bought them from didn't burn them in before matching.
...A lot of places are now charging extra if you want your tubes burned in before they match them, which is completely ridiculous. Burn-in is *essential* to matching tubes, so any vendor who skips that process, or charges extra for it- should be avoided. Tubes need to be ran under realistic voltages until they stabilize, BEFORE testing for the numbers used to match up sets, which should consist of both current draw and transconductance. Unfortunately, there are plenty of vendors out there who either don't know how to do it right, don't care, or don't want to spend the time required. When my company was selling a lot of glass, we did it right, and had the electric bills to prove it...

Even if I don't like them very much soundwise, they should work properly without the bias running away that much (though a certain bias drift with new tubes is normal).
I don't think they are "rebranded", they are made in the same factory like the new current production Tung Sol, Mullard, Svetlana and Sovtek tubes.
Of course I don't know if there's something wrong with your amp itself or if it's really the tubes.

I like the JJ EL34IIs. These were used by Marshall, too (with their label put on the tubes).
If you like more high mids and less bottom end, you could also try the Tung Sol EL34.
Even if I don't like them very much soundwise, they should work properly without the bias running away that much (though a certain bias drift with new tubes is normal).
I don't think they are "rebranded", they are made in the same factory like the new current production Tung Sol, Mullard, Svetlana and Sovtek tubes.
Of course I don't know if there's something wrong with your amp itself or if it's really the tubes.

I like the JJ EL34IIs. These were used by Marshall, too (with their label put on the tubes).
If you like more high mids and less bottom end, you could also try the Tung Sol EL34.
I may have jumped to a conclusion calling them garbage because I'm pretty pi**ed, but they are rebranded. I have 2 1987x's, 1 with the fx loop and an older 1 without and have used JJ El34s a few times in both with great results,I wanted to try the 6ca7s for a change. I haven't tried the IIs but I hear good things. As far as something wrong with the amp...... I'm not sure yet, after the new tubes and bias I put about 60 hours on it then had all the pots replaced, it was re-biased and the voltage checked out fine. I'm gonna check the voltage tomorrow and take it from there. The local shop that has tubes has the JJEL34s and the el34 IIs so Im gonna pick up a pair of each. THanks for taking the time to reply I appreciate it......
Even if I don't like them very much soundwise, they should work properly without the bias running away that much (though a certain bias drift with new tubes is normal).
I don't think they are "rebranded", they are made in the same factory like the new current production Tung Sol, Mullard, Svetlana and Sovtek tubes.
Of course I don't know if there's something wrong with your amp itself or if it's really the tubes.

I like the JJ EL34IIs. These were used by Marshall, too (with their label put on the tubes).
If you like more high mids and less bottom end, you could also try the Tung Sol EL34.
 

Minegoto11

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Voltages on Pin 5 identical? You could have a leaky coupling cap to the valve socket where the high bias is noticed...
Yea identical, plate voltage (pin 3 I believe) is identical as well.. I'm seeing quite a few people online with the same issue on different forums... a lot of them involve EH6ca7s
 

Minegoto11

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If you swap the 6CA7's between their two sockets, and the original tube that read 42 still reads 42 in the new socket position- your tubes have simply drifted out of match. It happens, particularly if whoever you bought them from didn't burn them in before matching.
...A lot of places are now charging extra if you want your tubes burned in before they match them, which is completely ridiculous. Burn-in is *essential* to matching tubes, so any vendor who skips that process, or charges extra for it- should be avoided. Tubes need to be ran under realistic voltages until they stabilize, BEFORE testing for the numbers used to match up sets, which should consist of both current draw and transconductance. Unfortunately, there are plenty of vendors out there who either don't know how to do it right, don't care, or don't want to spend the time required. When my company was selling a lot of glass, we did it right, and had the electric bills to prove it...
That's what I'm leaning toward... I also was told by a tech that the reissue EH6ca7s aren't a direct replacement for el34s.. I ordered a pair of apex matched and burned in el34s and a shop is holding a pair of jj el34IIs for me, I cant get over to pick them up till next week though... Thanks for the reply.. much appreciated
 

matttornado

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I have a quad of JJ 6Ca7s with a 10mA difference & I'm perfectly OK with it as my amp still sounds great. Not something I care about anymore as long as the amp sounds and performs as it should.

It used to bother me as well wondering if my amp would sound better with a closely matched quad but nope.
 

Mourguitars

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Please help me understand this , so if you have a quad ...3 test in close range in that 5mA or closer..and one is like 7ma low of the hottest one ..its ok if you dont bias hot ....correct ?

Not idea but is ok....... and I dont gig and run amp hard , and won't harm the amp...yes ? ( doesn't Gordon Ramsey ask a question followed up with a yes ? )...lol

I have a set of Apex EL34 that are new that came that way that i just opened but bought 8 months ago..out of warranty

I was buying a quad a tubes a month for 4 months to have some stash...kinda glad i did , next time i will test them. asap..lesson learned

I have a quad of old =C= like that also...7mA lower than the rest that are close ...im new to quads and not pairs

Kinda gun shy and learning , and to be honest is really anything perfect anymore...lol...like it to be !

Mike
 

mickeydg5

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Most of the time power tubes are matched within less than a 1mA difference.
Difference in bias from one side to the other of a push-pull may cause noise/hum usually starting by about 7mA while 10mA most always provides some sort of issue.

Swapping around or just reseating tubes can sometimes rid contact issues.

Always clean your tube pins and socket prongs with a decent electronic lubricating contact cleaner.
Make sure the socket prongs are tight fitting.
 

Minegoto11

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Most of the time power tubes are matched within less than a 1mA difference.
Difference in bias from one side to the other of a push-pull may cause noise/hum usually starting by about 7mA while 10mA most always provides some sort of issue.

Swapping around or just reseating tubes can sometimes rid contact issues.

Always clean your tube pins and socket prongs with a decent electronic lubricating contact cleaner.
Make sure the socket prongs are tight fitting.
Thanks for the reply, I tried all of the above with no improvement. It turns out it was the tubes.. Installed a new set of jjel34s on Friday and the amp sounds incredible.. thanks for the advice.
 

Minegoto11

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I put a new matched pair of EH 6ca7s in a 1987x that bandmates called the beast, (new preamp tubes as well) after it sat for a few years. The bias was set at 37ma with no issues and the beast was back! I had all the pots changed a few weeks later and the bias was checked, all good... I ran a gt8 with the 4cm and started "tone chasing". Something was off, but anyone who has a gt-8 knows there's a lot of annoying "tweaking". I'd get the tone close and the next day decide I wasn't happy and start over. It went down hill everytime I got close to what I want so I started thinking Im over doing it..... Last night I resert the gt8 and started from scratch.. Bam!!! sounded amazing, and went to bed happy.... Came home today and it was muddy and noisy, I checked the bias and 1 tube is at 31, tbe other at 42. swapped them and Its the same.... any suggestions?
I want to thank everyone for taking the time to reply and help resolve this very aggravating (to me anyway) issue. I installed a new pair of jjel34s Friday night and what a difference... I've put about 20 hours on it and it's getting better and better.... Now it sounds like a Plexi.. the beast is back, so far..
I'm gonna follow Moony's post and won't be buying electro harmonix again..
 

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