SVT-CL preamp tubes recommandations wanted

[Inconnu]

Hi !

I'm thinking about experimenting new preamp tubes on my SVT-CL because I have a bunch of 12ax7 tubes on hand. Here's what I've got, can you tell me what should sound good (or the difference of sound)?:
- Fender (Groove Tubes)
- NOS Phillips
- NOS General Electric (GE)

Thanks !

[kranahan]

try them out and tell us what you think...

[JimmyM]

you know, i can't tell one tube from another blindfolded but the philips tubes are very nice and usually last a long time. but i've had good luck with ge's as well, and i just had a tube emergency a couple months ago and got a fender groove tubes 12ax7 that seems to be doing pretty well so far in my super reverb.

[Eskimo Spy]

Not to hijack, but where are the other two 12ax7 tubes located in the new CL? I see the three tubes right by the back, the 6 power tubes...

[johnk_10]

out of all the tubes you mention, the philips would most likely be my favs, but every tube varies, has it's own voice, and sound different in different circuits, so you never know until to try them yourself.

[Inconnu]

Eskimo Spy : The 2 preamp tubes you are looking for are just under the front panel. Unscrew the 4 screws on top of the head and pull out the front panel. The tubes are there. AFAIK, preamp tubes where always there on SVT-CLs, mine is a 1995 model and they are placed there.

Others : well I guess I'll have to try the tubes out!

[coreyfyfe]

That's where mine were as well and I bought it new around 2005/6. You just have to dig em out. The tubes in the back near the power tubes are the splitter and driver tubes.

[iiipopes]

The only thing I would caution is to get a good NOS 12DW7 for the intermediate gain stage, per the factory tube spec chart, because the circuit is matched to the internal impedance of this particular tube. Some guys have their amps converted to use all 12AX7's in the preamp stages, "for convenience," and the one I had was like that. But I also got to record with an unmodified one, and the unmodified head had a broader, rounder, yet still present tone.

[coreyfyfe]

Originally Posted by iiipopes

The only thing I would caution is to get a good NOS 12DW7 for the intermediate gain stage, per the factory tube spec chart, because the circuit is matched to the internal impedance of this particular tube. Some guys have their amps converted to use all 12AX7's in the preamp stages, "for convenience," and the one I had was like that. But I also got to record with an unmodified one, and the unmodified head had a broader, rounder, yet still present tone.

There are no 12DW7s in the SVT-CL, it was designed around 12AX7s.

[Eskimo Spy]

Well, that sucked. I had noticed something rattling when I turned up the gain, and so I started checking screws. As it turns out, one of the screws that hold on the front panel (one of the four screws on the top, looking at the head, the back right one) was loose. Since you can see the nut and screw from the back of the head, I looked through the metal screen in the back, and the screw wasn't even in the nut! It was pushing the entire head down in the back. It took a little work, but I finally got the nut to accept the screw, but it appears to be stripped. There were metal shaving in the head as well, but I cleaned those out.

I may replace those sovtek preamp tubes, but I want to get the screw/nut problems resolved first.

I'll be calling Sweetwater later to find out what they can do about it, since I don't have any desire to do that again.

[Eskimo Spy]

Sweetwater will swap out the head with a new one, no problem. This is why I like doing business with them.

[iiipopes]

Originally Posted by coreyfyfe

There are no 12DW7s in the SVT-CL, it was designed around 12AX7s.

Pardon me. I thought you were referring to an original 12DW7. The 12DW7 is an important tube in the older original design, because it takes the 1st gain stage which is necessarily high impedance for the pickup input off the bass, and buffers it to low impedance to drive the rest of the circuit through the phase inverter and the power stage. You've just told me one reason not to ever get a CL, because that tube is necessary so that enough current at the lower internal impedance can be passed in order to maintain the headroom from stage to stage. Since a guitar amp doesn't necessarily reproduce the lowest frequencies required by bass, it's not so critical that a guitar amp be able to pass as much current along, hence 12AX7's and 12AT7's being more prevelant, and a 12DW7 almost unheard of in commercial guitar amp design.

[okcrum]

Originally Posted by iiipopes

Pardon me. I thought you were referring to an original 12DW7. The 12DW7 is an important tube in the older original design, because it takes the 1st gain stage which is necessarily high impedance for the pickup input off the bass, and buffers it to low impedance to drive the rest of the circuit through the phase inverter and the power stage. You've just told me one reason not to ever get a CL, because that tube is necessary so that enough current at the lower internal impedance can be passed in order to maintain the headroom from stage to stage. Since a guitar amp doesn't necessarily reproduce the lowest frequencies required by bass, it's not so critical that a guitar amp be able to pass as much current along, hence 12AX7's and 12AT7's being more prevelant, and a 12DW7 almost unheard of in commercial guitar amp design.

The preamp tubes in CLs also convert high impedance to low. There's nothing special about a 12DW7 doing that. The gain structure of a CL works just fine as far as headroom goes. So I'm not understanding how this is somehow a reason not to get a CL. Nor do I understand any of your post about guitar amps, current, etc. above. That's not at all how tube amps work.