Fender SCXD tube swaps, anyone?

Gear_Junky

Gear_Junky

New member
Hi. I'm curious to hear different experiences with replacing the 12ax7 and possibly the 6V6's.

I was told by an engineer that the way SCXD is designed, none of the tube swaps will produce a stark difference.

But I've also read of people getting a better tone with even just a 12ax7 swap. (on the SCXD 12ax7 is not a "preamp", it's half-2nd stage gain, half-PI).

Thanks!

P.S. Also, what about rebiasing for power tubes?
 
Gear_Junky said:
Hi. I'm curious to hear different experiences with replacing the 12ax7 and possibly the 6V6's.

I was told by an engineer that the way SCXD is designed, none of the tube swaps will produce a stark difference.

But I've also read of people getting a better tone with even just a 12ax7 swap. (on the SCXD 12ax7 is not a "preamp", it's half-2nd stage gain, half-PI).

Thanks!

P.S. Also, what about rebiasing for power tubes?
Click to expand...

Are you using the stock speaker in that amp?
 
sorry, i forgot to mention - i installed a jensen p10r alnico speaker. very sweet (although the stock one was pretty good).

it seems that people get different stock SCXD tubes, some are bad, others are good (like mine). I guess that determines how drastic (or marginal) the improvements are.

In my case I really LOVE my tone, but always wonder if there's anything else to be done.

I was able to A/B the amp with a Fender Hot Rod Deluxe (1x12) and other than the obvious cabinet differences the tone was suspiciously similar.
 
in some respects, your engineer friend is correct--it won't make as big a difference as if it were a preamp tube. (the SCXD and VCXD have solidstate preamps and a tube PI and power section) however, swapping the PI may help change the distortion characteristics somewhat. i wouldn't expect a dramatic change--but you might find things a little sweeter, gainier, whatever, depending on the tube used.

changing the power tube will also change the character of the amp somewhat, especially if you get it turned up to a point where it's really cookin.

always rebias after a power tube change.

as for what tubes? someone once said that picking tubes for someone's amp is like buying a shirt for someone you've never seen.

personally, i like the old ones. i'm a BIG fan of old RCA Blackplate and white-letter GE 12ax7's. As to 6V6's, i really, really dig the JAN (joint army navy) brown mustard base RCAs and the old circle logo smoked glass RCA Blackplates.

the RCA blackplate 12ax7s have a really nice high end--bright but not too strident coupled with an excellent low end. the GE's have a sparklier high end, not as much bottom....and more present mids than the RCAs.

a lot of folks will rave about telefunken 12ax7s as well.....nothing to complain about here. they're VERY hifi sounding to my ears.....almost to the point of being a little sterile. i like a lot of character in my amp tubes, and the teles i've used (both smooth and ribbed plates) aren't exactly what i'd consider character tubes. they're clean and smooth and more or less get out of the way of the amp, if that makes any sense.

i also like the made in holland amperex bugleboys. the ones i've used have been like a cross between the GE's and the telefunkens, but for the prices they go for, i'm not sure they're worth it. be sure that the ones you buy still read "made in holland", as "amperex bugle boy" is simply a relabelling (just like Groove Tubes), and "what's inside" can vary.

i haven't found a currently manufactured tube that i think can compete with old RCA and GEs in fender amps.....but the JJs aren't *bad*. of course, depending entirely on which JJ you end up with. :D

please understand that YMMV with tubes given their age, life left in em, and depending on the amp in which they're used. that said, i really think that if you were to outfit that thing with a nice set of RCA blackplates, you'll find things to be a degree or two of better.


cheers,
wade
 
Tubes are very much like wine. Some folks will go on and on about the nose, the finish, the complexity, the character, the balance, etc., ad infinitum. To others it's red wine or white wine, and that's about it.

Changing out tubes will either make a substantial difference in the sound of your amp, or none at all, depending on the design of your amp, which tubes you change, which tubes you had to begin with, and (most significantly) the subjectivity of your hearing.
 
thanks, guys! it's helpful, really! it tells me not to expect any drastic "miracles" and yet that it might be worth to experiment within reason, especially with 12ax7.

what about the TungSol's? I'm only asking cuz I've seen them available (and with good characteristics as far as noise and feedback).

I'm probably not gonna mess with power tubes any time soon unless I have to - i really don't have many tools to rebias (and never done it before). I do play at full volume occasionally (and it sounds good).

As to the 12ax7, I might even get several just for fun.

when I changed the speaker, it was similar - not a drastic change, but a slightly sweeter character, similar to when you replace decent stock pickups on a guitar.

funny you bring up wine. i can easily tell the really cheap ordinary wine from decent wine, but i still am not a big fan of dry wines. then again, some obnoxious oaky merlot (to me) can be "special" to someone else. point well taken. it's just still very helpful to have some pointers in the beginning.
 
Probably not worth it, if the 12AX7 really is just as a phase inverter, for the power amp...

The tung sols kick butt in the pre, especially (in my experience) with fairly high gain amplifiers - it really seemed to "open up" my Rectoverb when I swapped it out.

However, what you want in a phase inverter isn't a particularly sweet-sounding, musically-breaking-up tube, but rather a tube that is perfectly balanced. I'm a little fuzzy on the physics, but if you remember a typical class-AB power amp is a push/pull design, where when the signal's amplitude is all the way up on one side, it's all the way down on the other, etc, and at "rest" is flat. The phase inverter is what splits the signal. So, for a quiet, even-responding poweramp, it's really in your best interest to have each "side" of the poweramp getting exactly the same signal. That's what a balanced phase inverter tube is for.

If you have another tube amp around, toss the Tung Sol in V1 and rock out. If not, return it and track down a "balanced" 12AX7 for your phase inverter. I've had great experiences with JJ balanced 12ax7's, from Eurotubes, so my personal recommendaiton would be to start there.

Come to think of it, I still haven't replaced the stock phase inverter tube in my Rectoverb...

EDIT - also, I had no idea the Super Champ was a solid state pre and tube poweramp. Interesting...
 
I really like what I hear comin out of the Super Champ XD. It sounds authentic. I've owned and tried a lot of the modelers out there. They were all OK with the clean but just couldn't cut it with distortion or high gain. If you've got a decent axe, the SCXD is an excellant bedroom/recording amp. No need to change the speaker. It sounds good too. I did swap out the 12AX7 a few times and have settled on a good old Ruby Tube.
If you got an amp that gives you good clean sounds you like try the MXR III distortion pedal. Its has an authentic sound to it too. All the other pedals I tried have this buzz saw fuzz sound to them. The MXR nailed distortion right.
 
well, I agree, the stock speaker was pretty good. It's really just the "itch" to mod and there's always room for "better" :D I THINK I hear the difference - the Jensen seems a bit sweeter to me.

So, you tried several 12ax7's. Which ones and did you hear a diff? Thanks!

Bob's Mods said:
I really like what I hear comin out of the Super Champ XD. It sounds authentic. I've owned and tried a lot of the modelers out there. They were all OK with the clean but just couldn't cut it with distortion or high gain. If you've got a decent axe, the SCXD is an excellant bedroom/recording amp. No need to change the speaker. It sounds good too. I did swap out the 12AX7 a few times and have settled on a good old Ruby Tube.
If you got an amp that gives you good clean sounds you like try the MXR III distortion pedal. Its has an authentic sound to it too. All the other pedals I tried have this buzz saw fuzz sound to them. The MXR nailed distortion right.
Click to expand...
 
Well the original tube had a sort of grainy sound to it. I tried an NOS tube I had laying around and had a smoother response to it. I then plugged in a more current JJ 12ax7. The JJs can be clean and bright. I liked the JJ over the other two and did not experiment further. I ended up happiest with the JJ in place. The change is a was noted before subtle at best but its there. For me the JJ gave enough of a character change that I was satisfied and stopped there. I have a small number of select NOS tubes. Go for the JJ. Its reasonably priced and the small change is pleasing on the plus side of the equation. This is a such a great modeling amp. Great hi gain sounds.
These amps do come with differing tube sets in them however. Mine came with a set of Electro Harmonix in it. I did have one of these amps prior to the one I have now. It came with a set of Fender Groove tubes I think. I could tell the difference between the E-H and the F GT. The E-H set sounds better to my ears. I had to return the first amp because it stopped working within the first 30 days and got lucky with they gave me one with the E-H tubes.

As far as the speaker goes. It is worthy but I get the swap out bug too. I was toying with idea of installing a Ted Weber 10" Alnico Blue Pup but the existing one is good too. It rocks. To install the Blue Pup I'd have to remove the tube cage to get it fit anyway.

Its fun to experiment. When you customize your gear you give it your own special character. It becomes even more an extension of you.
 
I replaced the 12ax7 with the Tung-Sol I received yesterday. I played with the stock tube for a few minutes, let the amp cool down, leaving all controls the same, then swapped the tube and played again.

Stock tubes were all Electro Harmonix, russian tubes. So is the Tung-Sol. While this wasn't a "double-blind" test or anything, I thought I could hear VERY subtle differences, but not necessarily better or worse. Overall I'd say (just as I fully expected): if stock tubes are good, you can't expect any improvement big enough to matter, especially playing with others.

I am cool with that, I wanted to see what it's like to change tubes. I am keeping the Tung-Sol in there to see if maybe I'll start hearing something else there.

changing the speaker is VERY easy. yes, you have to remove the tube cage and the other panel on the back, but they're just 4 screws each.

just about EVERYONE who swapped in any kind of a brand name speaker reported considerable improvement (more than with tubes). I must agree.

Most people went with Ragin Cajun. It's possibly the loudest and covers all the models well (from what I read).

Some went with Jensen C10Q - they report that it's as close to original blackface amps as... the original.

I wanted the extra warmth, so had to make a "leap" based on what I read and went with the Jensen P10R (alnico). It's definitely warm or sweet.

Basically from what I read, the Jensen speakers will better cover the Fender models. I haven't played enough with the "brit" and hi-gain models of the SCXD, but I like mine ok. I'll have to play more.

I'd like to see more reviews of people putting a Celestion in their SCXD. It'd be interesting to see how the vox and marshall models of the SCXD sound through them. It'd be cool to have an external cab with a celestion to get different "amp" tones based on what you're doing.
 
The direct output on this amp is excellant too. All around this is a great bedroom amp for practice or recording either with a mic or direct in. It can get sparkle clean and singing sustain distortion. You do not have to crank it to the moon to get a reasonable signal level out of the direct output either. This amp covers all the bases for tones on the cheap. I have never been happier with a lower cost modeling amp.
 
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