Rca 7025/12ax7

[metlking]

Check out this old tube I've got. I have no idea where it came from, maybe from an old Ampeg V-4 I have somewhere. Anyway, for the last month or so I've been running it in V1 of my Bogner Ecstasy. I've been the most happy lately with my sound. I didn't think much about it untill I took it out and replaced it with a Tung-Sol reissue. I like the TS alot but with the switch the tone got harsh and gritty and unpleasent compared to the RCA. Old tubes really are better I guess! The problem is that this RCA is very microphonic and makes alot of noise. I can pretty much control the noise with my HUSH. The microphonic part is somewhat annoying. I'd like to see if I can find a NOS version of this.

Does anyone know anything more about this tube? Was it manufactured by RCA or someone else and labeled RCA? Made in what country?

 

[the guy who invented fire]

Re: Rca 7025/12ax7

NOS RCA 7025 tubes are out there still but get ready to pay for them...$100+ is not uncommon in terms of price plus be warned...you're Bogner might be a little hard on an old tube like that...Im not saying it will but it might and it would suck to drop that kind of green on a single tube and kill it in a short time.

 

[wahwah]

Re: Rca 7025/12ax7

That's a late 70's 7025, essentially a low noise version of a 12AX7 with an extra filament. The odd thing about it is that the plates seem quite dark, as opposed to the usual grey plates of that era. This might suggest that it was possibly manufactured elsewhere, maybe by Sylvania and branded RCA, although that would be unusual as they were in direct competition. Unusual, but not unheard of. That's a well made tube for that era, which is quite close to the end of the good tubes. The copper grid posts and long plates are a clue that it was made with care. If you like the sound of that, you should hear an original 50's RCA blackplate 12AX7, which is the tube you would have found stock in a 50's tweed Fender. They can be found regularly on eBay.

They look like this...

EDIT: I just wanted to add that you don't necessarily have to shell out the extra for NOS, you can quite often find excellent deals on "good used" tubes that have around 90% of their life left. The collectors don't want them because they're not pristine, but my amps don't seem to care! I've got about a dozen 50's RCA blackplates stored away, along with some beautiful early 60's Mullards. They were all bought "good used" and they last for years, under fairly constant touring/flying/gigging conditions. I'm happy to buy current production power tubes like SED's, but I refuse to waste money on current production preamp tubes when I can have the tone of these little gems! ~G~

Cheers....................................... wahwah

 

[glassman]

Re: Rca 7025/12ax7

The RCA script would indicate that the tube was manufactured sometime in the early 70's. The plate configuration (and color) looks like a Brimar to me.

 

[Curly]

Re: Rca 7025/12ax7

just to add ... that tube may be fine in a different position, but in V1 any microphonics are probably amplified by the following gain stages

 

[metlking]

Re: Rca 7025/12ax7

Thanks for the replys guys! I'm fascinated by those little bottles but never really got into the vintage stuff. I figured it was more or less internet hype!

The plates on the tube I have are not that dark in person, they do look black in the photo but are definately grey in color.

WahWah...I think I have one similar to the one you showed. It appears identical. It's labeled Magnavox and came from my Dads phonograph he had as a kid (50's) I haven't tried it as of yet. It has an odd square holo....never seen one like that.

 

[gOgIver]

Re: Rca 7025/12ax7

Used to have some of those in an old Silver Face Bassman 70 head. Closest I've found to them sound wise was a 12AT7.

 

[Curly]

Re: Rca 7025/12ax7

Myles has written about this quite a bit, but the specs were laid down by the old tube companies, and many of the current production tubes fall short as far as noise, gain, microphonics

some amp companies have subbed lower gain 12 AX7s to cut down on noise, but they often have less gain, therefore less dynamics to the amp

I have a stash of NOS tubes, and like wahwah, some old used tubes that work fine. I got them mainly for my vintage amps, but I'll use some in certain positions on amps I like, 'cause they sound better.

 

[wahwah]

Re: Rca 7025/12ax7

Thanks for the replys guys! I'm fascinated by those little bottles but never really got into the vintage stuff. I figured it was more or less internet hype!

The plates on the tube I have are not that dark in person, they do look black in the photo but are definately grey in color.

WahWah...I think I have one similar to the one you showed. It appears identical. It's labeled Magnavox and came from my Dads phonograph he had as a kid (50's) I haven't tried it as of yet. It has an odd square holo....never seen one like that.

Ok, so that grey plate makes more sense. It's from some time in the 70's.

RCA certainly relabeled for Magnavox, so it is likely that you have one of these beauties. If it has "12AX7" in a chalky white hexagon, it's definitely an RCA. They have the square getter, often referred to as a 'D' getter.

The thing about vintage preamp tubes is that they are often much more effective in vintage amps, or at least vintage style circuits. A lot of modern amps are built around $2 Chinese tubes, and as a result don't benefit greatly from having tubes from the "Golden Era." But in anything with a vintage style circuit, these tubes from the 50's and 60's will blow away any current production tube in terms of both tone and longevity. I've generally paid around $25-$30 for all of my vintage preamp tubes on eBay, and they include some of the finest tubes ever made, including the 50's blackplate RCA's and early 60's Mullards.

It's always advisable to look at 'good used' tubes, and specifically those that have been rebranded. Both RCA and Mullard made tubes for dozens of different name brands, and the 'collectors' aren't that interested because they don't have the original branding. It is also not necessary to buy NOS, because these tend to come at a ridiculous premium. A 'good used' RCA with 90% of its life left will last upwards of 5 years if it hasn't been trashed. I've had a couple in different amps since 2003 that do a lot of work and they show no signs of quitting, and added a wonderful new sonic dimension to the amps they are in.

The trick is to do your homework and learn what it is you're after, and then communicate with the seller to make sure that you know what you're getting. It's not for everybody, and I fully understand why many people would prefer to just use current production tubes, especially as I said, for modern design amps. Personally, I wouldn't waste the money on sub-standard current production stuff, because far from being internet hype, the best tubes from the 'Golden Era' are truly superior to anything made today, when put into a circuit that is ready for them.



Cheers................................... wahwah