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Photos - the death of a Simple SE and 6V6's

I was doing some testing of some tubes and transformers in a Simple SE board today. The results are posted here:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=124375

During that testing I remembered a box of 6V6's that I bought about 10 years ago. They were millitary bulk packed Sylvania 6V6GTA (not wafer based 6V6GTB as I incorrectly remembered earlier). The box of 100 tubes was still sealed when I got it. Upon opening I discovered that many of the tubes had lost their vacuum. I tossed them and saved the rest. Last year I needed some 6V6's so I reopened the box. More of the tubes had turned white. I tossed them. I reopened the box this evening, and found 7 more white tubes. What wood happen if I put these tubes in an amp? I set out to find out.

The poor Simple SE board that I am using has been through a lot. It has been used for all sorts of experiments including the 550 volt test. It was hacked up and made into a push pull amp:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=123320&highlight=

Then I put it all back together again to test some power transformers, so it is up for some more torture. I am going to name this one Buster!

Here is the line - up. there is one "normal" looking tube in the bunch. Note the silvery getter on the top of the tube on the right. All the others shoe varying degrees of air inside. DON'T PUT ANYTHING LIKE THESE IN YOUR AMP. You are about to see why.
 

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I tested the amp with a few of the normal looking tubes and they work fine. I have a Hammond 272KX power transformer which runs the 6V6 right at the maximum specs.

I selected a tube with some silver left showing. The amp worked, but the distortion was high. It rose from 3% to about 7% after 10 minutes and then stayed at 7%.

Next a tube with almost no silver left. It powered up OK the distortion started at 3.5% and took off almost immediately. There is a blue glow inside the plate.
 

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Bang, PFFFFFFT, then the smell of an exploded electrolytic capacitor fills the room. The amp had a 2 amp fuse in place of the usual 1 amp fuse, and it had blown. This photo shows the aftermath maybe 3 or 4 seconds after the fuse blew. The screen grid support rods were glowng red, and the cap was still spraying its guts into the air (the cloud to the upper right of the tube).

The cap is toast, but the amp does not work with good tubes in it. The autopsy will be tomorow. And maybe some more experiments.
 

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Well George, I assume you're doing this for fun since you surely knew what would happen. Maybe put a video on You Tube of a meltdown. You need some gassy 845's! I have a friend in upstate NY that once made some firecrackers with sulfur, aluminum powder and potassium perchlorate in a cardboard rug tube. That left a huge crater in the ground. Then the cops showed up and confiscated his chemicals.
 
You need some gassy 845's! ... I had an 845 go gassy on me. I still haven't bothered fixing the amp since the results were so disturbing.

Been there, blown that. I bought 2 211's at a hamfest for $5 for both. The guy said that they were "weak". I put one in my amp, and zap. Yes, it took out the driver circuitry but the main power supply was OK. I gave the tube to a retired ham who thought it looked cool. Of course, I "tested" it first, see photo.

I have a friend in upstate NY that once made some firecrackers

I used to do that too, 4th of July and New Years Eve were loud in my neighborhood. Since 911, it isn't a good idea to make these kind of things. They are not legal, and are no longer "overlooked".

Well George, I assume you're doing this for fun since you surely knew what would happen.

Yeah, I new that the tube would melt, but I kind of forgot about the cathode bypass cap. When the tube arced, the cathode resistor blew and the cap ate most of the B+. Poor 63 volt cap. Next time, there will be no cathode resistor!

Sad to see so many duds, how many actually survived out of the box?

There are about 40 left in the box. To this point these tubes have never been used. I am afraid to trust them in anything since they don't seem happy on the shelf in a closet in an air conditioned house. Every time I open the box there are more gassy tubes. I don't know how long the "good" tubes would last being thermally cycled in an amp. I plan to "test" a few more and see if I can meke a good one go bad. If so I guess they are all trash.

Funny, a pair of crummy ones that did that to me were Sylvania too. But they were yellow print.

In my usual "tube testing" I find that Sylvanias are consistently the most rugged. These are obviously a bad batch, or something happened to them before I got them, but I can't imagine what. I discovered another unusual thing. The 6V6GTA printing that is on the glass rubs off real easilly.

The moral of this story is, If you see a white getter, don't put it in your amp!
 

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Geek said:


I have two boxes here of those ^%$&%^ things :bawling:

*gets BB gun :devilr: *

Not necessarily the case that yours are bad, not yet time to panic. Check the getters.. They aren't necessarily from the same lot as George's and there may be specific storage conditions or a manufacturing error that caused this problem. I have many Sylvania tubes that are 50+ yrs old and none have lost their vacuum. The formerly NIB Sylvania 26s in my pre-amp are 66 years old and no problems over several years of use.
 
I set out to perform the autopsy, and found that the patient was still alive. I had yanked the power cord to the oscillator by mistake. The amp is still alive even with the exploded cap. There is this messy goo all over the PC board and all of the parts. I changed the cap, wiped up the goo put in some more of the Sylvanias and cranked it up again. OK it works, makes about 2.2 WPC and still sounds good, but this is BORING, and I got a box full of tubes to test.

What's next..... After thinking for a few milliseconds, it became perfectly obvious. I needed to answer the question. You know the question that I always ask. How much power can you get out of this thing. Well, even I know that exploring the upper limits will require gome glowing tubes, but I don't need any more exploding capacitors, and I need some more knobs to turn, so its time for fixed (adjustable) bias. No more resistors in the path to slow down the flow of POWER. Speaking of power, I am going to need some more. So I wired up the big Fluke. Now I can go to 550 volts and 300 mA. The tubes are not going to like this! I jumped the cathode resistor, and connected the bias terminals of the power supply up to the grid resistors.

At first I was running both channels, but I only have one bias knob, so I pulled one tube and decided to wire the remaining tube in UL mode. I put in one of the better looking Sylvanias and cranked it, and cranked it and finally just turned the power supply all the way up.

Thats right a 6V6 with 550 volts of B+, 535 volts across the tube. I decided to ignore the glow and set the bias for the best power and lowest distortion. Would you believe that a 6V6 can put out 10 watts at 3% distortion, 11.6 watts at 5% distortion, and 17.2 watts when driven to maximum power. The bias current was 100 mA. this means a static dissipation of 53 watts, minus the output power! Remember this is a 6V6 in SE! You must know what the tube looks like! As I said before, good Sylvanias are tough tubes.
 

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