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Post subject: Dead tube
Posted: Sat Sep 10, 2011 3:01 pm
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Aspiring Musician
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Joined: Fri Dec 12, 2008 5:32 pm
Posts: 329
I was having some fun with my vintage amps today.When i hit up my 78 vibrolux reverb. I turn it on and i get very little sound on the vibrato channel. So i check the normal channel it's ok perfect sound.

So now i am thinking i might have a bad solder joint in the vibrato section. I just shortened all the wires to V1&V2 recently.So i turn the amp on and use the chopstick test i don't hear any sound of bad joints

So i know i should of done this first but i take the tube shields off and i notice that V4 the filament is not glowing. So i quickly swap out for another 12ax7 and i got full sound.

So my question is has anybody just have a tube die like that.It sounded perfect last time i used the amp so sounds of any bad reverb.I was quite surprised to find a dead tube has this happened to anyone or should i be on the look out for anything else??


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Post subject: Re: Dead tube
Posted: Sat Sep 10, 2011 4:35 pm
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Rock Star
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Yup. Think of a tube's heater as a light bulb (a rather fancy light bulb). That's what light bulbs do sometimes, just go poof! Did this happen when the amp was "cold"--- that is it hasn't been played for a LONG time. And early in the morning, when the AC line from your outlet is at the highest voltage?

But, good detective work. Some ppl never find blown heater in tubes.

Variacs are nice things to have. Just for this reason.

http://www.ebay.com/itm/SUPERIOR-116B-P ... 3f0dd55fa0


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Post subject: Re: Dead tube
Posted: Sat Sep 10, 2011 7:50 pm
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Aspiring Musician
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Joined: Fri Dec 12, 2008 5:32 pm
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It just happened today when i started her up.I let her sit in standby for about a minute then i flipped her into play mode and faint sound. I would say that it has been a few days but no longer then week since i have used this amp last.


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Post subject: Re: Dead tube
Posted: Sat Sep 10, 2011 9:02 pm
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Rock Star
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Joncarr, may have happened in STANDBY mode. The heaters see full 6.3 VAC in standby. Or may have happen when you hit the standby and heated up the plates. As this is when there sometime is a current surge as voltage is applied to the anodes. But, I digress again...

Good catch! Good luck with new tube(s).


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