Zap-less tube changing

[Ripper]

My AVT 2000 combo needs its 1 ( one ) yes, I said ONE!
12AX7 tube, or ECC83 tube changed.

Ive done it on the past with my old all tube amps. This is the first time ive had to change the tube on this 50 w Marshall.

Am I gonna be okay??

Im hearing horror storys from friends about hybrid amps. Getting zapped etc.

Im just changing the tube. Nothing more. Are there areas of this amp I should steer clear of? Surely they could be no more dangerous then say, my all tube Crate amp?

[pollyshero]

You'll be fine. Change the tube as you would any other amp:

If the amp's on, turn it off.
Unplug the amp.
If you turned off the amp before unplugging wait a suitable period to allow the tube to cool down.
Using one hand only (put the other in your pocket), and ensuring that the hand you're pulling with is touching NOTHING but the glass of the tube, pull while gently moving the tube in a circular motion to remove it.
After removal, don't touch or apply your tongue to the tubes pins.

Good luck.

[Ripper]

Thanks Polly...Long time no see by the way!

Just curious...What part, if any is going to zap me?...The transformer?

[pollyshero]

I've been in self-imposed exile for a while - I was starting to "spout" instead of contribute so I figured I'd reel in my toungue for a while.

Anyway, from my own experience, just about ANY conductive component of a tube amp can bite. People get zapped for many reasons, but I would be willing to bet that unsafe handling practices are in the top percentage of incidents. Conversely, amps zap people for just as many reasons (actual malfunction not the fault of the operator). Unk or sumgai could give you a more definitive answer along with the whys and wherefores.

"Im hearing horror storys from friends about hybrid amps. Getting zapped etc."

If they are practicing safely and the amp's still zapping them, I'd say the amp is to blame & should be checked out by a qualified tech. I doubt there's any difference in "safety factor" between hybrid and all-tube amps - IMHO, ALL things electrical can be dangerous to the uninitiated, the foolish, and even the seasoned vet. I'd be interested to know how they're going about making the change.

Use care - If you're unsure of what "safe practice" constitutes, read any book on servicing tube amps - you'll usually find the safety stuff on page 1.

Cheers

[ChrisK]

Using one hand only (put the other in your pocket), and ensuring that the hand you're pulling with is touching NOTHING but the glass of the tube, pull while gently moving the tube in a circular motion to remove it.

If'n yer smart, you'll keep both hands in yer pockets and get someone else to do it.

Someone is always the "fuse".

[sumgai]

pollyshero said:

...........
IMHO, ALL things electrical can be dangerous to the uninitiated, the foolish, and even the seasoned vet.

Truer words are seldom spoken!

To get a good "rule of thumb" feel for what might be considered safe conduct, go back and re-read Chris's signature block. If you're about to monkey around where his signature would be untrue, revise your plans accordingly. (Failing that, please make me the beneficiary of your will.)

Again citing Chris, "Safety isn't, until you make it so."
[/sermon]

Pulling a tube isn't ordinarily a problem. The worst thing you'd likely encounter is the heat of the glass envelope. After doing so, you quickly remember the First Law of Physics: Hot glass looks exactly the same as cold glass! Enough burned fingers later, and your ability to remember that Law will assert itself before you touch the tube, trust me on this.

That said, your other major concern is that you insert the replacement tube without bending any of the pins. If the tube is giving you a real fight while going in, pull back! Check that you haven't bent any pins, then re-check your alignment with the socket. Failure to do so is a sure way to find your self doing the double-time march down to your local tube supplier, and giving the nice man all of your money for another tube. Slightly bent pins can be straightened, if done carefully. Fully bent-over pins are just waiting for you to attempt a rescue mission...... that's when Mr. Murphy makes his fabled appearance.

Rough-housing is for the 'rasslers on TV, finesse is for replacing tubes - got it? Good.

Horror stories? Got 'em, but don't need 'em. Just think about what you're doing first, and all should go well.

HTH


sumgai

[pollyshero]

Thanks for backstopping me 'gai - you addressed CHANGING a tube, where I merely addressed REMOVING a tube. I knew I could count on someone here.

[sumgai]

Polly,

Thanks for backstopping me 'gai - you addressed CHANGING a tube, where I merely addressed REMOVING a tube. I knew I could count on someone here.

All in a day's work.

Amps tend to work better with their tube complement fleshed out, hence it seemed a shame to not complete the cycle, at least it did to me.


sumgai

[UnklMickey]

pollyshero said:

I've been in self-imposed exile for a while - I was starting to "spout" instead of contribute so I figured I'd reel in my toungue for a while.

I don't know why you would do that. That never stopped me!



btw, I noticed your location is San Antonio. I though you had move to Austin.

[benitosuave]

If you want to be extra careful let it sit around unplugged and off for a few hours.

[sumgai]

benitosuave said:

If you want to be extra careful let it sit around unplugged and off for a few hours.

This is as opposed to sitting around unplugged and on for awhile? Must be a helluva battery in there...........

;D


Short story long............

One can change a tube safely (all other factors being taken into account) without disconnecting the power cord at all - IF the amp chassis is within the cabinet. That means, you can't stuff your fingers anywhere they don't belong. However, if the chassis is out of the cabinet, unplugging the power cord is in fact de rigeur - there are too many places in there that you can accidentally rest your hand, or drop items of interest that also conduct electricity, and then it's all over but the shouting. (And yes, I have seen a few amps like that, where the tube(s) was/were buried. Why, I'd really like to know too, but that's just the way it was.)

Even days of being off may not suffice - I've seen power supply filter caps retain a healthy, if not lethal, charge for months! May not ruin your day, getting zapped like that, but you will be p-o'ed for several minutes when you realize what just happened, and how much worse it could have been. Whenever you stick your hand inside a chassis, particularly a tube jobbie, just remember Chris's First Rule of Electricaly Safety........

[glow=red,2,300]Someone is always the fuse![/glow]
Try to make sure it ain't you!

HTH


sumgai