Suggest preamp tube (12AX7)

[überfuzz]

I'm about to place an order at thetubestore. I asked them to suggest preamp tubes to go in a twin reverb ab763 and they suggested something called, preferred series. They're probably just dandy, but I guess the extra $$ is for relabelling them... Is there anyone here that could suggest a 12AX7 tube that has a smooth break up, preferable late. I'm a really aggressive player that a sucker for big headroom.

Cheers!

Edit, by the way anyone tried their winged C 6L6 tubes in old-school fender amp?

[Jazz P Bass]

I don't know.
A Twin Reverb that breaks up?
(man you must play loud!)
To me, if it does, it will be in the power tube stage.
I think the tube manufactures 'prefer' to ship whatever comes off the assembly line.
So if someone selects a tube for something specific (like it is at the top of the bell curve) I guess that is a good thing.
(now get them to specify exactly what it is the are selecting, hah.)
To me, the Twin is a clean amp.
So looking for a preamp tube that 'breaks up' is kind of an oddity. (let alone finding what you want)

[überfuzz]

Yes, I play very aggressively. That being said, my preference is the lowest part of the break up spectrum.

Not sure I agree on the no break up in preamp tubes though part. I seem to get more with higain tube.

I guess my flyer is somewhat hard to understand, as hard as it is to explain how I like my amp to sound. Thanks for trying...

Edit, I guess I was hoping for a post like this: try this tube I have it in my fender and it rocks.

[Jazz P Bass]

As I may or may not have a specific tube to recommend, my point was, what are the chances of getting that tube again.
I have had new 12AT7 tubes that spec out (gain wise) as a 12AX7.
WTF.
Now someone gets a hold of one of these tubes.
Loves it.
Recommends it.
You go to get one and it is a real 12AT7.

It really is crap shoot, unfortunately.

[überfuzz]

You're right, didn't think about it like that. I guess it boils down to Chinese or Russian tubes then.

[Jazz P Bass]

Not necessarily.
I have seen Chinese 12AX7 tubes in a Peavey Classic 30, that where still strong, consistent & reliable, after touring for 4 years.
The same goes for Sovtek tubes.
My bitch is that they are not put through a sieve.

[pdf64]

I agree with Jazz, though given that, I found that the reverb driver stage causes break up in the AB763 pre-amp at a lower signal level than any of the other stages, given normal control settings.
Specifically, when the signal level rises above about 8V, the grid-cathode diode of the reverb driver clips off the upper part of the 'dry' signal quite harshly.
That can be greatly reduced by removing the bypass cap on the reverb driver cathode (or at least adding a series resistor to the cap, eg 470 ohms).
Of course the power amp is well into overdrive before any of that kicks in, so any difference may be 'subtle', but as you're looking to clean up the pre-amp, those were my findings.
I think it may go towards explaining why, when master vols came in with SF models, the reverb driver cathode circuit got messed with.
Pete

[überfuzz]

pdf64 - Interesting, I have noticed harsh break up, or distortion, like you describe. Mostly when I play garage rock alla the Sonics or similar. I never tried to figure out the reason my self, never scoped this amp.

Next time I gut my amp I'll definitely tinker with the reverb drivers bypass cap. Maybe I'll like the alterations you described.

Thanks!

[pdf64]

The main cause of nasty distortion on an AB763 type amp is often blocking distortion on the output tubes. This can be mitigated by reducing the coupling caps or grid leak resistors values; I've found that 0.047uF or 100k can make a significant improvement, also consider both together.
Reducing the global negative feedback on the power amp can help too. I like to remove it altogther, although for some guys that changes the character of the amp too much.
If you haven't already, try out doubling the 820 or halving the 100 ohm resistors.
Pete

[Justin Thomas]

Hi uberfuzz,

I have =C= 6L6s in my 67 Bassman. It's an AB165, but with the local - ve feedback removed from the power tubes and a bias adjust added, in addition to the Balance. They're twice as much as JJs but half of NOS. m The tubes started matched,but have drifted quite a bit... I haven't bothered to fix it because the amp still sounds great and doesn't make noise. I may fiddle with it later. They did get a rattle but I don't think it's a problem; it doesn't get amplified. One of them is also microphonic, but again, it's not causing any other issues. I'm VERY pleased with the sound; not sure if the rattle/microphonics would be an issue in a rocking Twin. If you like, I'll pop them in my 62 Concert (which has JJs in it and plate voltages ~500) and post any differences in sound. Then again, I haven't used any "generic" or NOS tubes in either of these amps. Hope it helps!

Justin

P.S. Yup, Twins (or Bassman 100s - Twin without effects) DISTORT, aren't THAT loud, and sound AWESOME!

PPS I'm with Steve on preamp tubes - I look for used ones in antique shops... cheap! Usually hafta buy the whole piece of equipment, though... I get a lot microphonic (not squealy) but not usually hissy or hummy.

[Steve A.]

I've heard good things about the TAD 12AX7's which I guess come in a regular and premium version (depending on whether the mfg/seller want more or less profit for the same damn tubes. ) I think I read that they are made by Shuguang in China.

Steve

P.S. I think that nothing beats NOS preamp tubes in the old Fenders.

[überfuzz]

I managed to dig up some of my old tubes, but they're running scares. Sooner or later I have to start using new fabricated tubes, it seems. Is there someone here using new made tubes that can shed some light on the matter. Pointers, dos, do nots and shit.? I feel completely lost... :-/

[oc disorder]

Found this comparison of 12AX7 tubes, which I thought quite informative.


https://www.tubesandmore.com/tech_co...ent_made_tubes


For instance the T-12AX7-FND the Groove Tube from Fender that is in most
new tube Fenders (G.T. tested Sovtek 12AX7WC) is low gain and low noise and favours
the low end.
Interestingly it shares the lowest noise figure (1) with the JJ Gold 12AX7 but the JJ has more
than double the voltage gain with no apparent disposition to favor one frequency over another.

[mflemmer2]

I'm about to place an order at thetubestore. I asked them to suggest preamp tubes to go in a twin reverb ab763 and they suggested something called, preferred series. They're probably just dandy, but I guess the extra $$ is for relabelling them... Is there anyone here that could suggest a 12AX7 tube that has a smooth break up, preferable late. I'm a really aggressive player that a sucker for big headroom.

Cheers!

Edit, by the way anyone tried their winged C 6L6 tubes in old-school fender amp?

überfuzz, I don't know if you've yet acquired your new preamp tubes, so this may be late advice. I'm planning on replacing my preamp tubes with The Tube Store's Preferred Series 7025. They ARE rebranded tubes (made at the Shuguang factory to exacting specs), but I've researched them ad-nauseum and they are the same tube as both the TAD 7025 S and the Ruby 12AX7AC7 . They are all based on the Mullard ECC83 from the 60's. The Tube Store sells both the TAD and (of course) the Preferred Series version, but the PF costs $6 less per tube---also, the PS has a 6 month warranty, and the TAD only 3 months. The Ruby version is available through Doug's Tubes. I haven't heard them yet myself, but they get consistently good (even great) reviews from multiple sources (not just tube vendors who sell them, either). I prefer working with the folks at The Tube Store (Sandra is especially awesome), because they take more time to work with you to ensure you're happy with your choices. Also, for $3 extra per tube, they'll test it for extra low noise/microphonics (a grade often referred to as HG+) for the V1 spot. TAD and Ruby actually sell this tube with both the HG and HG+ designation (the latter for more $) so it's the same idea---you just have to specify the HG+ testing with The Tube Store. NO, I don't work for them, and they're not paying me to say this---I just like the way they've dealt with me. Good luck, and Happy Holidays.

[tubeswell]

Just by a whole tub of them. There's bound to be one you like.