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Old 9th June 2008, 03:56 AM   #11
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I had an 845 go gassy on me. I still haven't bothered fixing the amp since the results were so disturbing. The 'lytics in the amp are rated at 3.2kv, but I think the grid bias supply for the 845 amp lost some caps.
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Old 9th June 2008, 08:46 AM   #12
Gordy is offline Gordy  United Kingdom
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George you make me smile.
Keep up the good work.
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Old 9th June 2008, 08:56 AM   #13
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Alllriiiight! Glowing tubes without the need to put them in the microwave

Funny, a pair of crummy ones that did that to me were Sylvania too. But they were yellow print.
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Old 9th June 2008, 01:07 PM   #14
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Quote:
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.

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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".

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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!

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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.

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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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Old 9th June 2008, 01:47 PM   #15
Yvesm is offline Yvesm  France
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The moral of the moral is

Be aware of (not so) lo priced bulk lots

Rejected, but stored ones, are starting to appear on the market.
Specially from WW2 era

Yves.
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Old 9th June 2008, 08:44 PM   #16
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Originally posted by Yvesm
The moral of the moral is

Be aware of (not so) lo priced bulk lots

Rejected, but stored ones, are starting to appear on the market.
Specially from WW2 era

Yves.
I have two boxes here of those ^%$&%^ things

*gets BB gun *
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Old 9th June 2008, 08:56 PM   #17
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by Geek


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

*gets BB gun *
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.
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Old 9th June 2008, 09:42 PM   #18
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I have two boxes here of those ^%$&%^ things

*gets BB gun *

Gives new meaning to the term "shootout".

Jeff
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Old 10th June 2008, 02:39 AM   #19
Vargas is offline Vargas  United States
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George, I always love reading about your adventures in tube testing. Bravo my friend.
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Old 10th June 2008, 02:43 AM   #20
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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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