RCA 12ax7

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Anitoli
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RCA 12ax7

Postby Anitoli » 20 Jan 2018, 16:15

Picked up an RCA 12ax7 rebranded as "Hammond" on E-Bay for $17. This tube tested really high, 106/109 for gain, 2435/2562 for Gm and -92Db for noise on both triodes. This is the first RCA old tube that i have been able to test myself and try in the V2 spot on my Blue Anniversary head. I now know why people claim these tubes are the cat's ass, because they are. Full sounding but no fizziness. Very, very sensitive to the input signal as a tube with that high a Mu should be. Gonna let it burn in that spot for a bit before drawing any final conclusions, but from what i am hearing now i like it.

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Re: RCA 12ax7

Postby surfnorthwest » 20 Jan 2018, 18:11

Yes they are the cats ass. I have RCAs in my Astoria and in V1 and V2 in my 2466. I can tell you I paid WAY more than you did, $17 is a steal.

https://www.ebay.com/itm/NOS-RCA-12AX7A ... 0005.m1851
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Re: RCA 12ax7

Postby Papus » 21 Jan 2018, 02:09

Lots of good valves languishing in unloved Hammond organs around the world.
Valves are treated much more gently in organs..... some have 75 year old valves still performing like new.
Unfortunately unscrupulous POS such as Analog Outfitters will not hesitate to trash a perfectly good organ just to get the valves, then they leave the wrecked carcass on the junk heap. Cunts.
Seriously brothers, next time you hear of any Hammond organs going cheap, or for free - snap them up. Salvage the valves for your guitar amps, replace with modern equivalents and pass the organ on to someone who will appreciate it.
Dime that puppy!!!

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Re: RCA 12ax7

Postby Anitoli » 21 Jan 2018, 13:34

Been playing around a bit with some tubes and i am noticing that the Gm (transconductance) seems to make a bigger impact on the tubes output than the gain does. On my tester the target gain number is 92. Even tubes that have gain lower than 92 but have higher Gm numbers sound better to my ears than the other way around.

Cool info on this site about tube codes:

http://www.tubemuseum.org/SearchResults.asp?Cat=30

EDIT: I used the wrong term for transconductance, it is Gm(umho) not Mu which is gain.

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Re: RCA 12ax7

Postby billy » 22 Jan 2018, 09:53

surfnorthwest wrote:Yes they are the cats ass. I have RCAs in my Astoria and in V1 and V2 in my 2466.


Ditto, ditto minus the Astoria, and ditto. I think I paid around $10 each for mine, but that was some time ago. I think Clinton was president...
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Re: RCA 12ax7

Postby billy » 22 Jan 2018, 09:56

Papus wrote:Lots of good valves languishing in unloved Hammond organs around the world.


I hear you and wish I had room for a Hammond.
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Re: RCA 12ax7

Postby Anitoli » 03 Feb 2018, 14:05

Got a few more RCA's made in the 50's for peanuts on EBay so i decided to try something. Obviously on a 6100 V1-V2 are the first stage triodes of the three channels so putting the good tubes there makes sense, so i started looking at at the PI and how that is the first stage for the power amp, so i stuck one of the RCA's in the PI and man did that make the amp open up. Everything is smoother and more fluid. There is a sharp increase in the clarity of the sound. On high gain the distortion is more defined.

Just to rule out any possibility of deceiving myself i did swap it in and out with other tubes and the differences were obvious. The worst tube in the PI was a GT ( JJ rebrand) harsh, brittle, cold, and sterile.

These old RCA tubes are the shit.
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Re: RCA 12ax7

Postby Alpeggio » 03 Feb 2018, 14:29

That's cool Pete.

My 800kk has stopped working and I'm hoping its the preamp valves, and not the milk bottle 88s.
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Re: RCA 12ax7

Postby Anitoli » 03 Feb 2018, 15:16

Did a fuse blow or just stopped making sound?

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Re: RCA 12ax7

Postby Alpeggio » 03 Feb 2018, 15:41

I'm not sure, I was recording with master volume on about 7, when it made a monster sound. I had noticed it was lacking gain, so pushed it harder, when it fizzled out.
No bang or anything, just a noise then silence.

Being a rock n roller, I just grabbed another amp and carried on recording. Didn't want to loose my train of thought.
Now though I've got to start figuring out what's wrong.
I'll look tomorrow. Btw all the 88s light up, so I assume that means the fuses are ok.
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Re: RCA 12ax7

Postby Anitoli » 03 Feb 2018, 15:50

If a power tube is shorted or drawing too much current a fuse will blow, depending on the amp usually the mains fuse. Preamp tubes will die but normally don't take out a fuse.

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Re: RCA 12ax7

Postby Dana,s blues » 04 Feb 2018, 13:41

There are some great RCA tubes. But there are a lot of bad ones as well. There was an RCA plant in Montreal when I was a Kid. My aunt worked there for a number of years. The ones that didn't test perfect were often relabeled as lesser known brands. Hammond would have used the best that RCA had to offer. RCA power tubes were really good tubes. They never had the notoriety of Mullard but some claim that they are fantastic in 50's and 60's Fender amps.

:Cheers

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Re: RCA 12ax7

Postby Doc Holliday » 04 Feb 2018, 14:49

I’ve got a few of everything. I like the RCA 6v6 tubes.
People rate them high. I’ve got the 50s smoked glass and the 60s grey plate.
They’re both slightly different. The black plate smoked glass being a little more midrange and better for tweedy tones. The grey plates are nice. Good clarity less murky.
I have a rebranded Marconi RCA 12AX7. Grey long plate. It’s a nice tube. Still prefer European tubes by far though. Brimar .. meh good all round , Mullard... I think these just sound great it vintage Marshall’s and Vox Tbh.
I like Philips, amprex , Valco etc. Great detail and bass response without being boomy. The clarity in the notes for me is what makes them better than the rest!
Favourite power tubes though are Ken rad!
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Re: RCA 12ax7

Postby Anitoli » 04 Feb 2018, 14:54

Yeah i am sure there are some duds out there, but i will gamble if the numbers are in the right range for the type of tester being used and the price is low enough.

I had gotten a quad of NOS RCA 6L6Gc's from an old guy that had a TV repair shop in 98 and i put them in my LM. I was gigging then and i still got 6 years out of those tubes.

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