I blew a tube!

[Cal Blacksmith]

I guess it had to happen sooner or later. I cranked up the

old 2ch rig last night (for the first time in like a month) and the left

channel didnt sound right. I changed LPs and things were the same. When I

bought the amp, The first thing I had done, was to replace the original Svetlana

6550 tubes with Old stock Tung sols (used tubes) and found 4 that would bias

correctly, however, I now had 2 that would not come up out of green, (green is

too low of a voltage, red it too high and no light is just right) So I put the

Svetlana tubes back in, adjusted the bias via the indicator lights. I had all 4

lights out, let it warm up for about 15 min, watching the indicator lights and

I played the LP again.

The music sounded like it had a wet blanket over it, very

muted (the reason I am sure, that this amp got some bad reviews when it first

came out, GOOD tubes fixed that problem), but the channel problem was still

there. I then shut everything off and got out my stash of old stock Tung Sols

again. As I have 6 of them and only need 4, I went through them and picked the

4 that looked identical, when installed however, only 2 would bias correctly. I

then played the game of switching tubes around until I had 3 that biased

correctly and one that nearly came up out of the green (the light grows dimmer

as you approach the correct voltage). Again I let things warm up for about 15

minutes while watching the bias indicators and all was right with the world (or

nearly so) I switched the amp into the normal mode of operation and dropped the

needle on the LP again and DARN IT that left channel problem was still there! I

switched the pre-amp to the tuner and the problem was gone! HMMMM, I have a

pre-amp problem. I then turned the pre-amp all the way down and cycled all the controls

to wipe the contacts and things were fixed when I rotated the input selectors!

GREAT, now I can settle down and listen!

Again I dropped the needle but this time things were as they

were supposed to be. I closed my eyes and settled in to listen. About 5 minutes

into the LP, I heard a crackle that was definitely not on the LP, I looked at

the amp and one of the 6550s was BRIGHT ORANGE! I got to the power switch at

the same time as the fuse blew, with no spare fuses on hand my night was done

though I did have other tubes I could use.

I didnt see anything abnormal with the other tubes when it

was on so I am hoping that there was no other damage. Any ideas as to what

happened? I can not say for sure that the tube that blew was in use before all

this started, it might have been on the edge all along. It was the tube that

biased correctly on the channel that had the other output tube slightly low in

voltage. I have found this condition before (one or more tubes low on bias

voltage) will no ill effects.

[Guest " "]

wow, thanks for sharing this, it's very informative for those of us that have been away from tubes for a few decades.

[Cal Blacksmith]

Bump

I really would like to know if I should just pop in another $65 tube and say LET her RIP! or is there something else I need to look at first?

[Bonzo]

I would certainly have it checked by a qualified tech.! I had a 6550 go cherry on me once and it turned out to be a bad resistor. $2 part as opposed to a $65 tube, if that is in fact what's wrong.

[NOSValves]

Cal,

I received your phone message and returned the call a few minutes ago but just got your machine. This problem could be a tube, leaky coupling cap or something in the bias circuit going south. I wouldn't chance another Tungsol 6550 on it. Since I'm fairly sure you have limited electrical experience I would say your best option on your end is to install all 4 of your original tubes (that your not so fond of) into the amp for a few days and see if any thing crops up. If it runs stable with the original tubes then you know one of the Tungsols just decided enough was enough. Its a shame but they really don't last forever. I would also advise you to clean the tube sockets with some deoxit and re-tension them so the metal contacts of the tube socket grab the tube pins nice and tight. Many times a run away tube can be nothing more then a tube pin losing contact from oxidization or a sloppy fit.

Craig

[Erik Mandaville]

*Safety Note:

You must be sure the storage charge in filter capacitors has bled off before working around tube sockets. Depending on the power supply design of your amp, shock hazard may be present even days after the amplifier has been turned off and unplugged. If you are unsure about the possibe presence of dangerous voltages, it would be a good to find someone who can help you.

Cleaning sockets is a great idea, just take precautions so you don't get shocked.

[pauln]

Tube rollers might keep a Sharpie on hand to label the tubes for identification - Sharpie ink won't be effected by the high temp of the glass. I had to roll about 8 preamp tubes to get a configuration of four that sounded dead quiet. With all the permutations of position it helps to know the individual tubes 'by name'.

The only tube I ever blew was one of the pair of 6L6 in my Fender guitar amp. Finishing the gig with only one half of the waveform sure sounded funny. Turns out one of the little known purposes of the power tube seems to be to protect the 1/4 watt 230K resistor connected to it.

[jt1stcav]

I feel your pain, Cal Blacksmith. I recently had one of my expensive TJ 300B mesh plate globes go south on me. Seems I was fortunant enough to catch it in time and there was no damage (that I can detect) to my amp, and after installing new entry-level Electro Harmonix 300BEHs, I'm back in the saddle again for the time being. But if your amp blew its fuse, then I assume you may have a problem that requires a tech's attention. Wish I could help you out...good luck with whatever decision you choose to make concerning your amp's well being.

[klipsch4life]

Try blowin' a Genalex KT88- that really hurts...

KG

[Allan Songer]

Someone around these parts who I will not name blew up an ENTIRE QUAD of NOS Western Electric 350B tubes!!! Now THAT hurts--BIG TIME--especially when it's 100% your fault!!!

I amost CRIED when Craig told me the story!!!

[johnyholiday]

Someone around these parts who I will not

name blew up an ENTIRE QUAD of NOS Western Electric 350B

tubes!!! Now THAT hurts--BIG TIME--especially when it's 100% your

fault!!!

I amost CRIED when Craig told me the story!!!

OUCH!...WE350b..OUCH AGAIN.. Sounds

like an output tube blew {hoping for the best}, NOS has it covered on

the tech side, output tubes do blow every couple of years ,,johny an

the "Thunder Crew" store em away labeled an cushioned jt1, johnys getting lonely where's my regular dose of insults! an go get an ohm meter! for goonie goonie goo goo's sake {LOVE THAT GUY "COMO NO"}

[sunburnwilly]

I turned off and unplugged my Quad 606 and Carver AV806x a week ago during a Heavy Thunderstorm ...

[Cal Blacksmith]

I just missed Craigs call;[] the phone was still ringing when

I picked it up to answer it. I called him back a little later and we talked for

about 15 minutes. What a fantastic asset he is to this forum. Thanks again

Craig![][]

Well, following his advice, I stopped by Rat Shack and picked

up the set of soldering tools (to tighten sockets with) the Pro-Gold/Deoxit kit

and a package of slow blow fuses. The amp is supposed to take 3 ½ amp fuses and

all they had were 3 and 4 amp fuses so I bought both but installed the 3 amp

fuse.

The sockets on the power tubes have a spring type of contact,

not the normal C or the spider type, these sockets have two contacts coming in

from 180 degrees from each other and are springs into the hole where the tube

inserts. There was no way to tighten those that I could see so I cleaned them

and treated them with ProGold. The 6922 signal tubes were all tight but I

treated their sockets the same way, keeping all tubes in the original

orientation and locations.

I set the bias pots to center of travel and installed the

Svetlana tubes (the old Svetlana, now referred to as Winged C) into their original

sockets, (the tubes and sockets are marked), set the amp to mute (the settings

for the bias indicators to work on) and pushed the power button.[li]

At this point things turned rather uneventful. The tubes all

lit as normal, the bias indicators all showed green (as normal until the tubes

warm up a bit) then two of the indicators went out (showing that I had guessed

their adjustment very close) and the other two remained green until I adjusted them

to their operating settings. I then spent the next hour watching everything

very closely and watched the indicators flicker a little red then green then

normal etc as the air conditioner outside cycled on and off. After an hour of

this, I decided that it was time to listen to some music.[8]

I put the amp into standby, switched the amp into normal

position and took her off standby. The pre-amp which was warming up was

switched to tuner and the gain knob was turned up, everything sounded just

fine,[] I moved to the TT, I took the LP I had cued up the night before, gave

it a wipe with the carbon fiber brush, switched the pre-amp to TT and dropped

the needle. Those factory tubes never sounded so good. Rather a bit forward in

the mids but clear. They still didnt sound as good as the Tung Sols but they

are listenable for the next few days anyway. I played 3 LPs and had to go to

bed. I really think everything is ok [<)]and it was just time for the old tube to

go to that great audio convention in the sky.[ip]

[Cal Blacksmith]

Craig, this is what the amp looks like.

Thanks again for the help!

[Erik Mandaville]

*Safety note:

There can be harmful voltages stored in filter capacitors -- even if an amplifier is unplugged and turned off. If you are not sure whether a strong charge is still present, DO NOT simply decide to touch things inside your amplifier, including cleaning tube sockets. This charge will drain off over time, or in some cases quickly if a 'bleeder' circuit exists in the power supply. It is possible to drain the storage charge 'manually,' but that should not be done unless you know exactly what you are doing.

I know of specific cases where heavy charges in filter caps were in fact very effectively drained from a component -- that being by way of the body of a good-intentioned person messing around inside a component he thought was 'safe' because of the fact that it had been turned off and unplugged for half an hour. In other words, that guy received a very hard ZAP when he, using an uninsulated tool, unknowingly touched something he shouldn't have touched. If you are working inside a component with both hands, the charge can travel instantly through the arms, by way of the chest and heart. This can be extremely dangerous, particularly for those who may have a heart condition.

Because this case turned out well, does not mean that the same will be true in all instances. The equipment owned by people on this forum is diverse, and what may be true for one component may not be for another.

[Gilbert]

Well, better a tube than a ********.

[lwhaples]

I felt your pain last night. Getting ready to spin some vinyl and found

that one speaker not making music.The Dynaco MKIII was sitting

there dead. Blown fuse,changed it and it slowly blew. Changed the

rectifier tube,again blew a fuse. Changed the 6550's and again blew a

fuse. Quit,and went inside from the shop. This morn,I decided to try

the last two tubes.Been playing fine all day. Tonight I get to spin

again! Thanks for sharing your troubles.

Larry

[jt1stcav]

jt1, johnys getting lonely where's my regular dose of insults! an go get an ohm meter! for goonie goonie goo goo's sake

That's okay, Johny...I've got better things to do. I've got a multimeter, thank you very much. And since my SET amp uses auto biasing, the voltmeter doesn't get much use.

I'm glad to hear that these blown output tube stories all seem to have happy endings.[Y]

[Cal Blacksmith]

Eric, a safety note is always a good idea. My background,

though not in electronics, is in industrial electricity and good safety habits

around electricity are the norm. It looks like I am lazy when working on

energized circuits but in fact the hand in the pocket is to prevent just such

an event as you are talking about. Good non conductive boots and dry workplaces

are an aid also. The scariest time I ever had was working on a live residential

service, in the rain, standing in a mud puddle! Many times over extra caution

was used on that one!