Preamp Tube Replacement

Re: Preamp Tube Replacement

Postby zoooombiex » Tue Mar 15, 2011 9:40 am

some of the newer preamp tubes do have a larger circumference than old preamp tubes. however, they *should* still fit. whereas the old tubes will have some space between the edge of the tube and the metal shield, the newer ones will sometimes actually touch the shield. just make sure the pins are lined up properly and push it straight in. it will feel snug but i've never encountered a tube that literally wouldn't fit. out of curiosity, what brand of tube is it?

oh, and this may be obvious, but when you're lining up the tube to put it in, look for the gap between the pins on the tube, and line that gap up with the gap in the holes in the socket. if you happen to bend a tube pin you can probably straighten it out with a pair of pliers and try again.

I wouldn't mess with trying to take out the metal shield surrounding the tube. it's going to be a hassle and it is most likely unnecessary to remove it. (if you do remove it, the outer screw-off shield will have nothing to screw on to)

also, if the tubes have been in there a while it's not a bad idea to pull them in and out of the socket a few times every once in a while. that helps clear up the contacts. sometimes the tube can be perfectly fine but it is not making good contact and that can introduce scratching and noise that can be mistaken for a bad tube. (you can also spray some contact cleaner in the socket when the tube is out for even more cleaning)
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Re: Preamp Tube Replacement

Postby zoooombiex » Tue Mar 15, 2011 9:48 am

dleonard wrote: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?


following up...

you don't have to take the chassis out. you probably already did this but just unscrew the back wood panel to give you better access to the tubes. try turning the amp on its side so you aren't bending over and pushing the tube in upside down. get a lamp or flashlight so you can stick your head in the back of the amp and look directly down at the tube socket and see the holes for the pins.

also, keeping the amp low will extend the tube life, not shorten it. and using overdrives won't really affect the tube life.

are they they the stock fender tubes? modern fenders usually ship with pretty weak tubes. you should pretty much plan on replacing at least the first and third preamp tubes immediately.
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Postby dleonard » Tue Mar 15, 2011 9:52 am

Thanks. I tried to upload pictures of this but it said the file was too big to post. It's the 3rd preamp tube im replacing. I bought a TAD AT7 (i think thats the one...i know i bought the right one). I have to get this squared away by Thurs...2 gigs

also, its impossible to tell if the prongs are lined up properly or are bent when you're pushing in
Last edited by dleonard on Tue Mar 15, 2011 10:02 am, edited 1 time in total.
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Re: Preamp Tube Replacement

Postby zoooombiex » Tue Mar 15, 2011 9:55 am

dleonard wrote: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


more follow up .. should have read all these at once...

as noted above, the shield is normal and should stay in place.

if you are bending the prongs (pins) then the tube is not lined up properly. look at the bottom of the tube - there will be a larger gap between two of the pins. now stick your head inside the amp (see above - take off the top wood panel and put the amp on its side). look directly at the socket with a flashlight and you will see a bunch of holes, and there will be a larger gap between two of them. the gap between the pins lines up with the gap between the holes in the socket.

when the new tube is big it makes it a little harder to feel if the pins are lined up because you have to use more force to slide the tube in. once you've bent the pins, make sure you straighten them out properly. if you leave it bent or angled wrong, then it won't go in the socket even if the tube is otherwise aligned properly.
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Re:

Postby zoooombiex » Tue Mar 15, 2011 10:08 am

dleonard wrote:also, its impossible to tell if the prongs are lined up properly or are bent when you're pushing in


you'll need to really get your head in the amp to make sure they are lined up as you put the tube against the shield, and then push straight down.

if all else fails, the amp has two channels and perhaps you only use one? you could steal a tube from the other channel that might fit in more easily. but the new one really should go in. probably the worst you can do is trash the new tube and have to get another.
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Re: Preamp Tube Replacement

Postby JonnyBoy » Tue Mar 15, 2011 3:10 pm

how many guitar players does it take to put in a tube? :smile:


Question, does the old tube go back in easy? can you get that one in fine but the new one not?
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Re: Preamp Tube Replacement

Postby dleonard » Tue Mar 15, 2011 3:59 pm

I got the tube in ok....and it didn't solve the f'ing problem. I want to take a bat to this thing. The rest of the tubes light up fine, if thats any indication. I hate this amp
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Re: Preamp Tube Replacement

Postby FretfulDave » Tue Mar 15, 2011 4:35 pm

I should have checked this thread in depth sooner. I had something similar happen to me a couple years ago where I got to a jam and my amp just started fading. If I didn't play for a few minutes, it would come back and when I started playing, it would fade after a short time, a couple measures of a tune. I ended up attributing the problem to the power tubes, which upon pulling, looked pretty singed. I replaced them with the same as what came w/ the amp, a Peavey Classic 30, and I was off to the races again.

FWIW, in my research on tubes and readings, pre-amp tubes don't fail often and last a long time. It is usually the power tubes that burn out, change characteristics, etc. I do have to say that I suspected perhaps loose tubes after I had replaced the power tubes but the new ones were cleaner, less noisy, etc so I did not go back and check it. Couldn't hurt to pull and re-seat the power tubes and the other pre-amps as well. You never know.

As for the replacement tube you got, glad you finally got it in but hadn't heard of TAD tubes before. I checked some of my online shopping places and 1 store had a few of them but not many. The other main one did not carry them. I have no knowledge of them but would also think to stick with the "tried and true" common brands out there.

Good luck.

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Re: Preamp Tube Replacement

Postby JonnyBoy » Tue Mar 15, 2011 4:38 pm

TAD or Tube Amp Doctor are what Brad is using in his SMS I believe....
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Re: Preamp Tube Replacement

Postby FretfulDave » Tue Mar 15, 2011 4:48 pm

JonnyBoy wrote:TAD or Tube Amp Doctor are what Brad is using in his SMS I believe....


Fair enough, JB. I had not heard of them before and I went to their website and saw things like "extra thick glass walls" and such in the description and pondered if that was some of the trouble dleonard was having seating them. That's all.

If they are good enough for Mr Sarno, then I will take that as a fine recommendation.

My new amp is... well, new so don't think I will be needing any for a little while.

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Re: Preamp Tube Replacement

Postby zoooombiex » Tue Mar 15, 2011 10:48 pm

I think (but could be wrong) that TAD doesn't make tubes for itself but rather sources them from other manufacturers and they are checked for tighter specs. They're definitely solid tubes (whether you like them tonally is of course up to you).

It definitely could be the power tubes, but it might be worth taking it to a tech.

Also, in general looking at whether a tube looks bright is not a very accurate way of testing whether it is a problem. Unless it's completely black inside or the plates are glowing orange it probably won't tell you much.
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Re: Preamp Tube Replacement

Postby dleonard » Wed Mar 16, 2011 6:24 am

yeah...im just going to take it to a tech now.

Tennessee Jedi, does that guy in Hatboro do amps as well?
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Re: Preamp Tube Replacement

Postby Tennessee Jedi » Wed Mar 16, 2011 6:54 am

dleonard wrote:yeah...im just going to take it to a tech now.

Tennessee Jedi, does that guy in Hatboro do amps as well?

Not sure but if I had to guess I would say yes.
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