Tube amp/preamp incident

[Mike L]

I go to fire up the system in the usual patient process that firing up tubes take.  I turn on the source, then the pre (muted)...let them warm up for a bit and then fire up the monoblocks.  As the monoblocks are starting up I start to hear some noise out of the speakers and them see one of the 6922 input tubes flash.  I quickly turn the amps off followed by everything else.

After letting everything cool I then hook up the preamp to an Aragon amp and when I unmute the preamp there is noise coming out of the speakers.  I have had noise come out of the speakers before when I needed to replace the preamp tubes.  Obviously, the amp tubes and the preamp tubes wouldn't fail due to use at the same time.

Can a failure to an input tube on an amp cause damage upstream in the preamp?  Could a problem preamp tube cause an amp input tube to fail?  Could there be more problems than just the tubes?

Help....advice please.

Thanks,
Mike

[steve]

Hi Mike L,

     I suppose it is possible that the preamp could have damaged the amps grid on the input tube if the preamp had a strong RF oscillation. But it is not likely. This assumes your preamp has capacitive output coupling.

If the preamp has DC output coupling, this is easily possible if high voltage couples directly into the amps input grid and the mute switch is activated. I assume the amp tube arced before the mute switch was turned off though?

If the preamp is dc coupled to the amp, and if high voltage from the arc in the amp tube got on the grid, it could find its way back to the cathode of the preamp tube, but unless the voltage is quite high, can't see damage being done, Mike. Except to the amp tube which arc.

Maybe pop some old spares in and see if the noise persists.

Hope this helps.

[Mike L]

Thanks for the thorough response Steve.  I Appreciate it....I am too stupid to fully understand everything but that is another issue altogether.

I tested the tubes and found the 5687 input tubes on the amps to be very weak (all else was good).  I replaced those and everything seems to work okay now.  The amps themselves are quieter when first starting up as well.  I ran the preamp into a SS amp I have and it is working fine as well.  In hindsight I was switching things around and I may have possibly not made a proper RCA connection .

I don't have a lot of experience with tube amps and I have to admit that they scare me a little.  I either need to test the tubes more often or better recognize when they are close to expiration.

Anyway, a big sigh of relief here.

Thanks,
Mike

PS.  can a tube arc as you say and still survive?  I ask because I tested the tube that I thought that did this (it was a 6922) and it passed all of the tests and was still very strong.  I am wondering if it may have just been my imagination due to the uneasiness I was feeling while this was occurring.

[steve]

Thanks for the thorough response Steve.  I Appreciate it....I am too stupid to fully understand everything but that is another issue altogether.

I tested the tubes and found the 5687 input tubes on the amps to be very weak (all else was good).  I replaced those and everything seems to work okay now.  The amps themselves are quieter when first starting up as well.  I ran the preamp into a SS amp I have and it is working fine as well.  In hindsight I was switching things around and I may have possibly not made a proper RCA connection .

I don't have a lot of experience with tube amps and I have to admit that they scare me a little.  I either need to test the tubes more often or better recognize when they are close to expiration.

Anyway, a big sigh of relief here.

Thanks,
Mike

PS.  can a tube arc as you say and still survive?  I ask because I tested the tube that I thought that did this (it was a 6922) and it passed all of the tests and was still very strong.  I am wondering if it may have just been my imagination due to the uneasiness I was feeling while this was occurring.

Hi Mike,

     I would not worry as there are no 'stupid' questions Mike.

To answer your last question first, yes, a tube can arc and survive. Sometimes it just happens.

Tube equipment can seem intimidating. I think you are safe if you make sure the chassis is closed at all times. Especially with kids, you might consider some sort of shield to keep them away in case they should tumble and break a tube and get hurt.

I would not worry about the noise from the preamp unless it flares up again. All is ok Mike. You are amonst friends.

Hope this helps.

[richidoo]

I used to have the seem feeling of helplessness, panic, something really bad happened when I started with tubes. After several incidents of tube giving out or being fried before I learned how to zero bias before swapping tubes I gradually learned that tubes are pretty easy to deal with, and are usually simple and reliable. If you accept that tubes are commodity parts that will eventually go bad, like lihgtbulbs then you can prepare and to be frustrated when they eventually go. Keeping spares around, even if not the greatest quality is a good idea to keep the music flowing, and don't forget the fuses. Most well designed tube equipment has adequate fuse protection to prevent any real damage and allo you to fix most everything yourself. This is very handy compared to shipping an amp away for repair. It is definitely scray when a tube blows, especially when you are near the amp, but with a little knowledge most tube blowups can be avoided, and gradual wear and noise is the only inconvenience, plus the occasional fuse.

Glad it is all better now Mike

[Mike L]

Thanks Rich.

Mike