Preamp Tube Replacement

Preamp Tube Replacement

Postby dleonard » Wed Mar 02, 2011 7:49 am

I posted a while back about my amp (Twin RI) sort of fading out when i would play it. It sort of came and went for a bit, but as of the past week it is fading completely out the instant I play anything. A friend of mine told me to check to see if all the tubes are glowing in the back because it sounded, to him, to be an issue with a bad tube. I turned the amp on in a dark room, and sure enough, what I think are one of the preamp tubes (the small ones inside the metal case?) is not[b][/b] glowing. Is this something I can replace on my own? If so, can I pick one of these tubes up at guitar center or sam ash? Does this even make sense to be the cause of the problem? I don't know sh*t about electronics or anything.

Thanks
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Re: Preamp Tube Replacement

Postby JonnyBoy » Wed Mar 02, 2011 8:41 am

How old are they? it may be time for a full replacement if one has reached its life expectancy, especially if they were all installed at the same time. The tubes Brad is using in the SMS Classic are affordable and good quality. Follow his site to the retailer. You will need four(4)- 12AX7's and two(2) 12AT7's. You should have a tube chart on the amp, if not it is online very easy. There are Youtube vids about changing tubes... If the amp is relatively new, just replace that one tube.

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Re: Preamp Tube Replacement

Postby tigerstrat » Wed Mar 02, 2011 8:49 am

dleonard wrote:I posted a while back about my amp (Twin RI) sort of fading out when i would play it. It sort of came and went for a bit, but as of the past week it is fading completely out the instant I play anything. A friend of mine told me to check to see if all the tubes are glowing in the back because it sounded, to him, to be an issue with a bad tube. I turned the amp on in a dark room, and sure enough, what I think are one of the preamp tubes (the small ones inside the metal case?) is not[b][/b] glowing. Is this something I can replace on my own? If so, can I pick one of these tubes up at guitar center or sam ash? Does this even make sense to be the cause of the problem? I don't know sh*t about electronics or anything.

Thanks


Yep, that's your problem and it's easily user-replaceable. The large (power) tubes are the ones you need to replace as a set and require a bias adjustment, but preamp tubes are freely swappable. Consult the tube chart on the inside of the cabinet to see if it needs to be a 7025, 12ax7, or 12at7 type.
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Re: Preamp Tube Replacement

Postby dleonard » Wed Mar 02, 2011 8:53 am

hmmm ok...Am I going to need to take the chassis out of the amp? If so, im reluctant because I could defintely F*** it up

BTW...the amp and tubes are about 3 and a hald years old. Does keeping the amp low and always diming my guitar with a tubescreamer and mxr+ often on contribute to tubes going bad sooner?
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Re: Preamp Tube Replacement

Postby JonnyBoy » Wed Mar 02, 2011 10:00 am

Dunno if that wears them out faster, but if you are using it every day and its been 3-4 years it wouln't hurt to replace them all, but they still probably have more life, or could be used as spares.

TS is right you can swap out the bad one only (without doing anything but removing the tube cover and unplugging the tube by pulling it straight downwards) and let that be that.
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Re: Preamp Tube Replacement

Postby dleonard » Wed Mar 02, 2011 10:08 am

perfect, dudes...thanks alot
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Re: Preamp Tube Replacement

Postby strumminsix » Wed Mar 02, 2011 11:07 am

FTR I often swap powermp tubes w/o a bias adjustment. Shit some of our favorite records were recorded with tubes mis-matched sets an unbiased amps. Sure, tubes were of better quality then but come on, no worries in my mind.
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Re: Preamp Tube Replacement

Postby dleonard » Wed Mar 09, 2011 5:20 pm

ok so the tube came in the mail, i go to put in the replacement, and i cant get this damn thing in. There is this metal piece that surrounds the socket that is making it impossible to line up and get in. Any experience with this?
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Re: Preamp Tube Replacement

Postby rugger » Wed Mar 09, 2011 5:59 pm

The metal shield? Twist and pull down. Pretty easy to remove.

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Re: Preamp Tube Replacement

Postby dleonard » Wed Mar 09, 2011 6:08 pm

There is a seperate one that surrounds the socket after i take the first metal cover off. It covers about half of the tube, and it is not seperating from the socket. It is screwed onto the chassis as well. I tried inserting the tube with it on there but i just keeo bending the prongs. I knew this couldnt be so easy
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Re: Preamp Tube Replacement

Postby mkaufman » Wed Mar 09, 2011 6:16 pm

If you were able to pull out the old tube, you should be able to put in the new tube, as long as you have the prongs aligned properly, plus, there may be a notch allowing you to put the tube in oriented in a specific way. Don't force it - you'll bend/break the prongs.

However...before you do anything - did the old tube come out completely? Is there a possibility that the glass portion separated from the plastic base? I've seen this happen. If so, take the remainder of the tube out and then you'll be ok.

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Re: Preamp Tube Replacement

Postby dleonard » Wed Mar 09, 2011 6:26 pm

the metal cover was gripping the old tube from the base, so now when i am trying to insert the new one...it is not allowing me to even get the prongs to the socket without applying force
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Re: Preamp Tube Replacement

Postby jdsmodulus » Wed Mar 09, 2011 7:49 pm

Can you take a picture of the amp socket? Also take a pic of both the old tube and the new tube, prongs and all! Maybe then we can get a better idea of what is happening.
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Re: Preamp Tube Replacement

Postby JonnyBoy » Wed Mar 09, 2011 10:15 pm

We are talking about the small preamp tubes not the larger power tubes correct? My reissue does not have a second metal "protection" barrier to deal with. I would think if those are removable, just take them off. It may be overkill as long as you have the other covers. Preamp tubes can be a hassle to line up right if you have never done it before, as I do remember my first time. You have to reinsert them exactly how they were removed, or it is like putting a square peg into a round hole, it won't work. There is only one way they will go back. if they are aligned correctly, then the sockets on the chasis are tight or bent, so this may be the issue. You did mention this is a new amp... you could possibly remove the amp chassis from the cab and view the insertion from the top as you are doing it to make sure. You can also see from this top view if the socket has a bent connection rings keeping it from inserting properly. It should take some force in a new socket to reinsert, but you will know when it is aligned right or not when pushing. They do make a lubricant/cleaner to help with this too I believe. If you bend the pins too bad it could loose its vacuum by cracking the glass slightly around the pin. it may be worth a trip to the music store to have them do it at this point. Good Luck!
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Re: Preamp Tube Replacement

Postby TI4-1009 » Thu Mar 10, 2011 7:31 am

See this is why I really liked my first amp. I took a Heathkit audio amplifier my Dad had put together and screwed it onto the top of a plywood speaker cab I made. OK, so it was a little topheavy, fragile (and dangerous), but it sure was easy to change tubes! Having to use 1/4">RCA adaptors always made me feel like it wasn't a "real" guitar amp. "We've come a long way, baby!" :wink:
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