SVT CL AMPEG retube

[mike 54]

I'm a tube amp rookie. I have a 1999 SVT CL that I am retubing. I love the warm motown sound the older SVT's give up. I just want to know if in the preamp I should put in the old 12DW7's they used in the earlier models or do I just replace the 12AX7 and 12AU7's that are in there? And is there a specific brand of 12AX7 that would give me a warmer tone? Please school me in this tube arena. I love the sound and I want to continue playing through a tube amp. Thanks,.....Mike. PS I will be using new 6550 EH tubes

[Tom Phillips]

Mike,
The SVT CL is very much different than that of the older SVT that used the 12DW7. So, although it probably won't destroy anything if you install 12DW7s, it won't make your CL sound like an old SVT. If you do put 12DW7s in the pre-amp then two of the four stages will have lower gain. Maybe that will be your ticket but I have never heard any reports of this being done. I would not change the 12AU7s which are in the power amp driver stage. Note: Make sure you follow the bias adjustment instructions in your users manual when you install new power tubes.
Regards,
Tom

[Enzo]

Listen to Tom. The new SVT is a reissue, meaning they remade something with todays technology to be more or less equivalent to the old model and have similar specs. What they did NOT do is simply start making the old ones again.

[Rick Erickson]

Listen to Tom and Enzo, then listen to me. If you put a 12AU7 type tube (1/2 of the 12DW7) where a 12AX7 was you will likely damage your plate resistor(s) as the voltage drop across them will increase dramatically. These kinds of tube swaps aren't nearly as plug-and-play as some websites would lead you to believe.

RE

[John_H]

Mike; Your preamp tubes are probably fine. They should outlast a few sets of output tubes. You could however experiment with different brands. Vintage RCA, GE, and Telefunkens are all good choices. Sometimes hard to find, but worth the effort. Welcome to the forums.

[mike 54]

Thanks!

Thanks for all the valuble info! I will experiment with the older 12AX7 tubes and see how they sound. Is it worth going vintage on the 12AU7's? Thank's again guy's! Mike

[Amp Kat]

The SVT Classic has two different sections of preamp tubes. In the front of the amp where the power switch and controls are two 12AX7's that are mounted on a pcb board. If you want to experiment that's where you may want to try some different 12AX7's. The master pcb is a two layer board that the other preamp and phase inverter use. I wouldn't toy mismatching those tubes as others allready have pointed out. The bias controls on the back use two pots with a reference voltage op-amp thingy and when it gets to a certain reference it turns the leds either red or green. The range is not to large and you can hear the hum if you crank it to much and the red leds will glow. IMO this bias circuit is very inaccurate as the lights don't allways mean correct bias especially if there are mismatched tubes used. I like to connect speakers up to it and throw a flourescent light over it and crank the bias pots for minimal hum. You can arrange the sixtet array before that to get a good balance of somewhat green led action but usually one is green and one is off. Of course when you play they light up with signal swing. You also may consider tightning those power tranformer bolts and maybe putting some locktite on them as if you play loud those screws will back themselves off and fall on the power board wreaking havoc. Seen this twice on those amps but like allmost any of the SVT series they are great sounding bass amps,loud as hell,powerful and heavy.

[mac1amps]

I've also upgraded the drive tubes [from 12AU7's] to 12BH7's on a few newer SVT's. Not so much for trying to make it sound like an older one (let's face it, NOTHING sounds like an older [and properly working] SVT), but the 12BH7's will last longer.