Power off or okay on when swapping preamp tubes?

[75lespaul]

As you guys know, I got that Marshall Silver Jubilee combo and it had a Tung-sol in v1, and Sovteks in V2 & 3. I put two brand new Tung-Sols in it but the shhhhhhh noise coming from the amp is WAY worse than with the Sovteks. It's so bad that when not playing, the noise is nearly as loud as the amp is! I was going to take three brand new GT tubes that sound great and noiseless and put them in the Jubilee, then if the noise is gone or less, pull one and put a Tung-Sol in its place until I find the problem tube. Can I do the single tube at a time testing with the amp on? I saw a tech do it once but I was a bit surprised as I thought you had to power down when swapping tubes.

Also, as far as power tubes, can you swap them and play for a few minutes without biasing just to see if they are the sound you want, or will that damage the amp or tubes? Plus, does biasing affect the sound where I really wouldn't hear the true sound anyway.

Thanks guys. Gotta learn this stuff sometime.

 

[jeremy]

Re: Power off or okay on when swapping preamp tubes?

i wouldnt swap tubes with the amp on

you can listen to tubes with out biasing and youll get some of the character of those tubes but if the bias is way off it wont be a good snapshot

 

[Scott_F]

Re: Power off or okay on when swapping preamp tubes?

For any tube swap, safety dictates that you turn off the amp completely. IT doesn't take very much time to warm up the tubes anyway. The risk is a bent pin causing a short (could need repair) or if the tube was to break in your hand and you've got a handful of high voltage as your reward, ... might want to power that amp off.


I actually had an old tube just disintegrate in my hand one time.

 

[YJM_Rocks]

Re: Power off or okay on when swapping preamp tubes?

Don't tubes get a little toasty when they're on? Yes.

 

[75lespaul]

Re: Power off or okay on when swapping preamp tubes?

Don't tubes get a little toasty when they're on? Yes.

That's okay--I've got asbestos fingers :laugh2:

 

[YJM_Rocks]

Re: Power off or okay on when swapping preamp tubes?

 

[75lespaul]

Re: Power off or okay on when swapping preamp tubes?

For any tube swap, safety dictates that you turn off the amp completely. IT doesn't take very much time to warm up the tubes anyway. The risk is a bent pin causing a short (could need repair) or if the tube was to break in your hand and you've got a handful of high voltage as your reward, ... might want to power that amp off.


I actually had an old tube just disintegrate in my hand one time.

Okay, I'm sooooo convinced it's not funny. :bad: < however that's funny

That would be my luck. I could picture my conversation with Kurt, Jimi, Bonham, Lynott etc...

Kurt: "Yeah man, I shot myself"
Jimi: "Man, I partied until I choked on my own puke"
Bonzo: "Eh, mate, me too!"
Phil Lynott: "Me too!"
Me: "Um....I was changing a preamp tube...the glass broke....Um...that's it..." as they blankly stare at me and silently walk away.

 

[Gearjoneser]

Re: Power off or okay on when swapping preamp tubes?

I'm wondering what that hiss is. Highgain amps have a little, but something doesn't sound right, and it may not be the tubes. It's either the bias or maybe a bad filter cap or something.

That amp is now officially 20 years old, so it may be a good time for a full checkup by a tech who really knows his stuff. New tubes, bias, maybe a pot or two changed out, and track down the source of that noise.

 

[J Moose]

Re: Power off or okay on when swapping preamp tubes?

I'm wondering what that hiss is. Highgain amps have a little, but something doesn't sound right, and it may not be the tubes. It's either the bias or maybe a bad filter cap or something.

That amp is now officially 20 years old, so it may be a good time for a full checkup by a tech who really knows his stuff. New tubes, bias, maybe a pot or two changed out, and track down the source of that noise.

I'm thinking caps...maybe not filter caps, maybe in the pre or EQ section...but probably caps.

At 20 years it's about or even past due for a complete recap. Laws of physics dictate that every 10-15 years the electrolytics should be replaced for optimum tone & before anything fails.

 

[75lespaul]

Re: Power off or okay on when swapping preamp tubes?

I'm thinking caps as well. Hoping tubes, but thinking caps.

 

[75lespaul]

Re: Power off or okay on when swapping preamp tubes?

Progress!! Swapped the Gts from the 73 into the Jubilee and the Tung-sols into the 73. The Tung-sols sounded good in the 73, but it was a bit noisier. The Jubilee did NOT like the GT Mullards. It was feeding back even with the guitar's volume all the way down! Never had THAT happen before. The noise was way lower though.

Okay, so I swapped them back and once again the 73 is really quiet--for a Marshall--and sounds ungodly. The Jubilee is still ultra noisy. Then I took the Tung-Sol out of V1, which was the one that came with the amp (the other two are brand new) and put a JJ ECC83S in its place. Took away about 75% of the noise. Still didn't sound great though so I put the two Sovtek tubes back in that came with the amp and voila--awesome tone. I normally don't like Sovteks, but this amp seems to like the JJs and Sovteks. It's still noisy so I'll have it checked out, but the noise sounds to me like slightly above a reasonable level for a higher gain tube amp. I wonder if the power tubes could be causing the rest of the noise, or if its some caps. Next stop, techland!

 

[Scott_F]

Re: Power off or okay on when swapping preamp tubes?

Okay, I'm sooooo convinced it's not funny. :bad: < however that's funny

That would be my luck. I could picture my conversation with Kurt, Jimi, Bonham, Lynott etc...

Kurt: "Yeah man, I shot myself"
Jimi: "Man, I partied until I choked on my own puke"
Bonzo: "Eh, mate, me too!"
Phil Lynott: "Me too!"
Me: "Um....I was changing a preamp tube...the glass broke....Um...that's it..." as they blankly stare at me and silently walk away.

Now, that is funny!

 

[Scott_F]

Re: Power off or okay on when swapping preamp tubes?

Carbon comp resistors can get noisy over time as well. Electrolytic caps are like changing the oil in your car. You just have to do it after so many miles. In the case of caps, it's 10 years as a good rule of thumb. The problem with I see is that folks go nuts and start changing out coupling caps as well and they end up wondering why their amp sounds a bit different when they're done.

 

[MVI]

Re: Power off or okay on when swapping preamp tubes?

I'm thinking of the movie "The Ghost Busters" when "Ray" ( ? ) explains the risk of crossing stream paths of their ghost sabres - or whatever they're called : " Imagine every molecule in the Universe exploding at the speed of light ", to which Bill Murray's character responds : " OK, good safety tip ".

Always turn OFF the amp. Even if it seems like the lamest satety overkill in the world. Also, it would be nice to drain down the caps by leaving in the standby position for sometime ( I know this is asking a lot ), before reaching in and monkeying with anything significant. A condom, spacesuit, manual, and eye protection are also recommended, depending on any concurrent activities. But seriously, there's a bunch of electrons in there !