And then there was one: second amp has failed

Alright, bad update but here we go with some video evidence. I ordered a new set of Svetlana EL34s and four Sovtek 12AX7-LPS. As mentioned before, I changed the HT fuse and replaced the JJ EL34Ls with an older set of Svetlanas I had, to which the bias was adjusted down to 41mV and both potentiometers were holding fine in that configuration. Based on that? I assumed all was well

But when installing the new tubes, I did a check on the bias again and this occured: i noticed that each potentiometer was at 46mV. I immediately turned them down to the lowest settings. V7 held fine but V6 began to climb. This video shows exactly the process and what's happening

Is this a bias drift?
 
And it gets weirder!

I put the old tubes back in, left the potentiometers back to their lowest setting. Watch this

Why would old tubes hold steady and brand new ones start climbing? What would be the reason of this? Not burned in properly?
 
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Clockworkmike said:
Alright, bad update but here we go with some video evidence. I ordered a new set of Svetlana EL34s and four Sovtek 12AX7-LPS. As mentioned before, I changed the HT fuse and replaced the JJ EL34Ls with an older set of Svetlanas I had, to which the bias was adjusted down to 41mV and both potentiometers were holding fine in that configuration. Based on that? I assumed all was well

But when installing the new tubes, I did a check on the bias again and this occured: i noticed that each potentiometer was at 46mV. I immediately turned them down to the lowest settings. V7 held fine but V6 began to climb. This video shows exactly the process and what's happening

Is this a bias drift?
Click to expand...
Swap positions. I bet one of the new tubes suffers from an early demise
 
CoyotesGator said:
Probably. Doesn't necessarily mean that you are out of the woods.

Follow AMS's advice for sure.
Click to expand...
I certainly have used his information well and abided by his instructions to the letter: been a massive help!

The old Svetlanas hold their bias mV without any increases whatsoever, as does one of these tubes, even when swapping positions , which has been about 34.5mV with the potentiometer at its lowest setting. The other starts out at about 40.5mV is climbing steadily. Initially it was about .1mV per second and now it's about .3mV per second.

Again, checking the other? Still holds at 34.5mV And even going back to the old tubes: holding steady but at a lower mV ( I Would assume they are lesser due to their age?)
 
Clockworkmike said:
I certainly have used his information well and abided by his instructions to the letter: been a massive help!

The old Svetlanas hold their bias mV without any increases whatsoever, as does one of these tubes, even when swapping positions , which has been about 34.5mV with the potentiometer at its lowest setting. The other starts out at about 40.5mV is climbing steadily. Initially it was about .1mV per second and now it's about .3mV per second.

Again, checking the other? Still holds at 34.5mV And even going back to the old tubes: holding steady but at a lower mV ( I Would assume they are lesser due to their age?)
Click to expand...
Seems like the bias is fine. Just a faulty tube. Use the Svets till they sound ass. Lower Mv on the old ones simply cause of how they were made. Adjustable bias on amps because of that - variance in tubes.
 
Jethro Rocker said:
Seems like the bias is fine. Just a faulty tube. Use the Svets till they sound ass. Lower Mv on the old ones simply cause of how they were made. Adjustable bias on amps because of that - variance in tubes.
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Good deal, my friend! I'm sending these back, as they're covered under returns. I'll try again with another set, but switch back to the old trusty ones in the meantime. Kinda crazy: tubes are like 10 years old and had a lot of miles on them but still work and sound fine actually lol
 
Clockworkmike said:
Good deal, my friend! I'm sending these back, as they're covered under returns. I'll try again with another set, but switch back to the old trusty ones in the meantime. Kinda crazy: tubes are like 10 years old and had a lot of miles on them but still work and sound fine actually lol
Click to expand...
Given an average of say 2500 - 5000 hrs minimum, depending how hard you push 'em, it takes a long time to kill a set of tubes unless something else happened to them.

In 10 years that's around 500 hrs a year of hard use. An hr plus per day on average.
 
Clockworkmike said:
Alright, bad update but here we go with some video evidence. I ordered a new set of Svetlana EL34s and four Sovtek 12AX7-LPS. As mentioned before, I changed the HT fuse and replaced the JJ EL34Ls with an older set of Svetlanas I had, to which the bias was adjusted down to 41mV and both potentiometers were holding fine in that configuration. Based on that? I assumed all was well

But when installing the new tubes, I did a check on the bias again and this occured: i noticed that each potentiometer was at 46mV. I immediately turned them down to the lowest settings. V7 held fine but V6 began to climb. This video shows exactly the process and what's happening

Is this a bias drift?
Click to expand...
Which amp are you working on?
Are you calling old svetlanas "new tubes?"
Or did you install NEW UN-used svetlanas, and the bias of V6 began to climb?
Which was it?

OK let me explain:
When EL34s are used in defect DSL amplifiers, it damages the tubes.
Once the tube is damaged, the current will climb higher and higher and it won't stay steady.
The tube has been wrecked, and it can't be used in any amplifier anymore, it's junk.
No matter what amp you put this damaged tube into, the current will go wild, higher and higher.

I have seen several sets of brand new tubes, turned into junk by installing them into a defect DSL amp..

And this is "why" we are being so cautious. We don't want to wreck any new tubes.

Where did you buy these "new" svetlanas from?

Don't try to play the amp, wait until we analyze this more.
 
And one more thing to consider:

Consumer Tube testers are less than 50% accurate.
Normal tube tester misses 7 out of 11 possible defects.

Consumer tube tester does not test, or detect:
Microphonic tubes (ringing squealing feedback and oscillation)
Loose internal construction
Bad frequency response
Excessive harmonic distortion
Excessive Hum and Buzz
Crackles, static, popping noises (very common in old preamp tubes)
Runaway current of damaged / defective power tubes (tester will tell you a defect tube is "good.")

This is what a Tube Lab Test does:
Looks for ALL possible problems. Especially the problems that a normal consumer tube tester ignores.
Checks for ALL 11 possible defects (above).

This is the issue:
Tubes are tested using a normal consumer tube tester.
The problems are ignored. (see above)
The tube is "bad," and the tester tells you it's "good."
Then the vendor sells you the defective tube....which supposedly tests "good."
Now you have paid for a defective tube.
Oh, joy. :BH::BH::BH:
 
Amp Mad Scientist said:
Which amp are you working on?
Are you calling old svetlanas "new tubes?"
Or did you install NEW UN-used svetlanas, and the bias of V6 began to climb?
Which was it?

OK let me explain:
When EL34s are used in defect DSL amplifiers, it damages the tubes.
Once the tube is damaged, the current will climb higher and higher and it won't stay steady.
The tube has been wrecked, and it can't be used in any amplifier anymore, it's junk.
No matter what amp you put this damaged tube into, the current will go wild, higher and higher.

I have seen several sets of brand new tubes, turned into junk by installing them into a defect DSL amp..

And this is "why" we are being so cautious. We don't want to wreck any new tubes.

Where did you buy these "new" svetlanas from?

Don't try to play the amp, wait until we analyze this more.
Click to expand...
This is the DSL50 actually. What had happened was about 4-5 years ago, I changed the tubes from the "old" Svetlana EL34s I had in it to JJ EL34Ls. Then over a week ago, the amp just faded out and went silent, blowing the HT fuse. I never attempted to reuse the JJs and tossed them in the trash assuming at least one had failed. After ordering some replacement fuses and following your testing instructions, I reinstalled the previous Svetlanas which are now roughly 10 years old and the amp was able to be biased and stable without any issues

Since the amp appeared to be fine, I had ordered a new, unopened pair of Svetlanas online from a seller on Ebay to replace the old ones. This is what you see in the first video, where as the old tubes are in the second video. The new Svetlanas has one tube climbing up in DC millivolts at a rate of roughly .3mV per seconds while the other is completely stable. I changed positions of each tube and the problem follows the tube, not the socket, which tells me the tube is bad? To verify this, I reinstalled the old previous Svetlanas and the bias is stable at each tube and even when they are swapped in position, without any issues
 
Clockworkmike said:
This is the DSL50 actually. What had happened was about 4-5 years ago, I changed the tubes from the "old" Svetlana EL34s I had in it to JJ EL34Ls. Then over a week ago, the amp just faded out and went silent, blowing the HT fuse. I never attempted to reuse the JJs and tossed them in the trash assuming at least one had failed. After ordering some replacement fuses and following your testing instructions, I reinstalled the previous Svetlanas which are now roughly 10 years old and the amp was able to be biased and stable without any issues

Since the amp appeared to be fine, I had ordered a new, unopened pair of Svetlanas online from a seller on Ebay to replace the old ones. This is what you see in the first video, where as the old tubes are in the second video. The new Svetlanas has one tube climbing up in DC millivolts at a rate of roughly .3mV per seconds while the other is completely stable. I changed positions of each tube and the problem follows the tube, not the socket, which tells me the tube is bad? To verify this, I reinstalled the old previous Svetlanas and the bias is stable at each tube and even when they are swapped in position, without any issues
Click to expand...
Yes I see
you bought tubes from somebody on e bay...
50% chance they knew the tube was bad when they sold it to you. I am guessing this person was dumping his defects on you.

It's become very popular to sell junk tubes on e bay. Don't fall for it.

Old Used junk tubes that are called "NOS" the seller claims that the tube "tests good."
And of course it's garbage. You wouldn't believe how many people have been scammed by this.
There are boxes of old wasted junk tubes and people are selling them to UN-suspecting victims.

"NOS" means new old stock. A new tube that has never been used...
An old used tube can never be called "NOS."
But the vendors are selling the old used junk tubes, and calling them "NOS."
Claiming that the old used junk "tests the same" as NOS.

My friend bought 10 of these "NOS" preamp tubes from ebay, and 8 of them were trash.
Only 1 or 2 out of 10, actually worked right.

So my advice is: never buy old used tubes, or tubes that are called "NOS."
Always buy only new tubes; and only from reputable highly trusted well known sources. Avoid buying from e bay especially.
 
Amp Mad Scientist said:
Yes I see
you bought tubes from somebody on e bay...
50% chance they knew the tube was bad when they sold it to you. I am guessing this person was dumping his defects on you.

It's become very popular to sell junk tubes on e bay. Don't fall for it.

Old Used junk tubes that are called "NOS" the seller claims that the tube "tests good."
And of course it's garbage. You wouldn't believe how many people have been scammed by this.
There are boxes of old wasted junk tubes and people are selling them to UN-suspecting victims.

"NOS" means new old stock. A new tube that has never been used...
An old used tube can never be called "NOS."
But the vendors are selling the old used junk tubes, and calling them "NOS."
Claiming that the old used junk "tests the same" as NOS.

My friend bought 10 of these "NOS" preamp tubes from ebay, and 8 of them were trash.
Only 1 or 2 out of 10, actually worked right.

So my advice is: never buy old used tubes, or tubes that are called "NOS."
Always buy only new tubes; and only from reputable highly trusted well known sources. Avoid buying from e bay especially.
Click to expand...
Yeah i agree. I've never bought NOS or used tubes, just ones labeled as new and unopened. But in this case, I think I got burned. But, good deal is I got the shipping label to return them and the seller can deal with them. I guess I'll go to Sweetwater or Zzounds and order some direct
 
Clockworkmike said:
But in this case, I think I got burned.
Click to expand...
I’m going to assume that it wasn’t intentional. Crazy stuff has and will happen in the process of shipping products to your door. Fortunately your questionable new set of tubes has some type of warranty. Maybe you can consider giving the vendor a chance to make it right. And hopefully your DSL’s only issue was a failed power tube… :fingersx:
 
Clockworkmike said:
Yeah i agree. I've never bought NOS or used tubes, just ones labeled as new and unopened. But in this case, I think I got burned. But, good deal is I got the shipping label to return them and the seller can deal with them. I guess I'll go to Sweetwater or Zzounds and order some direct
Click to expand...
Tube Depot has been good for me.
 
syscokid said:
I’m going to assume that it wasn’t intentional. Crazy stuff has and will happen in the process of shipping products to your door. Fortunately your questionable new set of tubes has some type of warranty. Maybe you can consider giving the vendor a chance to make it right. And hopefully your DSL’s only issue was a failed power tube… :fingersx:
Click to expand...
I don't think he burned me intentionally, rather he didn't check his stock properly. The tubes were marked as being matched with a red sticker that said 37 on them in pen. Usually, that means they checked and matched them but either that wasn't the case here OR, is it possible it could've been damaged in shipping, because let's face it: a glass valve filled with gases isn't exactly robust and rigid against the USPS. But, no harm really: he did accept a return without issue. If he wanted to reship some new ones? I'd be fine giving a second chance.

In the meantime, was checking Tube Depot
 
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