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changing tubes in a SVT-CL mid 90's

hydrohydra

hydrohydra

Guest
Mar 15, 2012
794
388
Detroit Michigan
#1
i recently bought a svt and i want to replace all the tubes, im going to get 6 tungsol 6550's, 3 Electro Harmonix 12AX7EH's
i wanted to know if it was safe to replace the two 12AU7's with two more 12AX7EH's? also, could anyone runn my through the process of taking the tubes out of the amp?
 
#2
No, don't replace the 12au7's with anything but 12au7's. The 12ax7 has way more gain and isn't intended to be used in the spots where the 12au7's are.

As for replacing all the tubes, may I ask why? Does your amp sound bad? Retubing an entire amp at once is the biggest waste of money in the world. Tubes don't just wear out because they get old, and they don't wear out at the same speed. Do what you want, but my advice is if it ain't broke, don't fix it. Replace only your broken tubes, and if you break a single power tube, at the most you should only have to replace 3 to keep the matching happening. But certainly not all 6.

As for taking the tubes out, not sure about where all the tubes are since I don't have a CL at the moment, but it's very easy and straightforward. Pop the old one out, pop the new one in. There might be retainers around the power tubes you might have to unsnap, but it's a very easy procedure that anyone can do. Just remember to unplug the amp first ;)
 
#4
Worn tubes sound bad. Loosing bass, definition and punch. You will notice it, until then why change? Those preamp tubes are designed to run thousands of hours, change only when they go microphonic. You can test it with turning the amp full on, and tap on the tubes gently with a tip of a pencil. If they audible rang like a bell or start screeching or rattling change them. If it's just the sound of tapping the pencil, (it's audible) you are good to go. You can do the same test with the power tubes. If you hear the filament rattling, (strange rattling metallic noise, but it's not coming from the speakers and heard only on specific notes/frquencies.) don't swap tubes, buy a couple of tube dampers and be done.
 
#5
Different tubes sound different. Lots of guys roll tubes looking for their tone. Is it cheap ? No, But neither is the latest pedal, a new bass, a new cabinet. However if you dont even know how to pull the tubes out your defiantly going to need a tech to make sure it properly biased.
 
#7
thanks for all the advice guys, i am new to the tube game, but i have narrowed it down as this, my tone and all setting is flabby and clinky, less when i use my 4x10 1x15 cab but still noticeable, after play for a little while i check my tubes visually and in my second row of my power section one of my 6550's doesnt seem to be glowing but im biased in on the back of the svt perfectly so this should tell me power being even distributed through my power hence my power tube couldnt have gone out (right?) also a amp tech i talked to said where the tube is positioned in the head might make it less visible to check if its glowing or not because of the retainers that cover the tube, if all this is true his telling me that this undesired tone my be coming from a micro-phonic pre amp tube, i hope this is true. also i certainly dont wont pay a amp tech to put in a pre-amp tube for me but ive seem to be lost in my svt, ive think i found the three driver tube inputs because theres three preamp tube input in front of my power tubes, now i can seem to find the other two, although i haven't looked to hard. suggestions to my world of confusion?
 
#8
Four screws on the top, then the preamp slides out from the front and your tubes are now accessible. Getting the preamp back in can be a tad tricky but not too hard.

For microphones you can gently tap each tube while listening to the speaker output. You'll know if one is noisy.

Good luck.
 
#14
Those lights in the back are so you don't have to take it to a tech to bias it, you should be able to adjust those two little pots in the back so you get the two green LEDs in but not the red ones, I was told you can turn it down so the green lights just turn off to bias it a little cooler without any negative effect on sound.. when you're playing you'll see the red LEDs light up which is normal. I'd say if in doubt take it to a tech. I haven't lived in Vancouver for a decade but when I was there Ho's electronics was the place to take an Ampeg, not sure if he's still there.
 
#16
toomanyslurpees said:
Those lights in the back are so you don't have to take it to a tech to bias it, you should be able to adjust those two little pots in the back so you get the two green LEDs in but not the red ones, I was told you can turn it down so the green lights just turn off to bias it a little cooler without any negative effect on sound.. when you're playing you'll see the red LEDs light up which is normal. I'd say if in doubt take it to a tech. I haven't lived in Vancouver for a decade but when I was there Ho's electronics was the place to take an Ampeg, not sure if he's still there.
Click to expand...

That is NOT true. The ONLY way you can ACCURATELY Bias new tubes is with voltage check. Those lights on the back are CRAP .

I owned one.
 
#18
im still having doubts but apart of me thinks it might just be the the one power tube that wont light up in the back row in the middle, i can see all other five glowing brightly, but that one doesnt seem to be powered on at all, still trying to avoid the tech.
should i just try to replacing a few power tubes first before going?
 

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