It is currently Mon Mar 16, 2020 9:05 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 143 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6, 7 ... 10  Next
Go to page Previous  1, 2, 3, 4, 5, 6, 7 ... 10  Next
Author Message
Post subject: Re: 12AX7/7025 Tubes
Posted: Fri Apr 18, 2014 2:23 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14045
Location: Province de Québec, Canada
cedarblues wrote:
This is probably a silly question, but is it safe to swap preamp tubes while the amp is on or on standby? I always turn it completely off before I remove any tube. This could be very helpful when tube rolling :)

No No No !

I've got some more preamp tubes on the way, including the Psvane, hopefully I can try some this weekend...


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: 12AX7/7025 Tubes
Posted: Fri Apr 18, 2014 3:37 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Cedar, the heater line is still fully operational with the Standby switch engaged. Best not to suddenly pull or insert tube under those conditions.

You have to give us a report on those PSVANE tubes. I've only heard a few reports of Marshall users and this tube. They liken the tone to the early 1960 Mullard long plates. That would be nice, if true.


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Fri Apr 18, 2014 5:29 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Sat May 22, 2010 10:53 pm
Posts: 1467
Location: deep down in Florida...
Then I'll stick to the way I've been doing it...

No Psvane yet, but I did get these two...

Image

Image

Just tried both real quick, nice clean sounding, prefer the RCA... I'm glad I found another NOS that sounds great! The Sylvania is nice, but seems a bit low on output, but I like the clean tone.


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Sun Apr 20, 2014 12:40 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Those square getter, black plate RCA tubes are rare birds, these days. Whatever brand/era you choose, the tube must test high across both triodes. And be most quiet of the lot. If you compare a tube which tests 150% versus a tube that tests only 85% --- the higher testing tube will sound better 99% of the time. No matter who made what.

I guarantee that if you roll Sylvania square getter BP or Raytheon 12AX7A black plates that are quiet and test over 100%, you will not be disappointed.


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Sun Apr 20, 2014 7:49 am
Offline
Professional Musician
Professional Musician
User avatar

Joined: Sat May 22, 2010 10:53 pm
Posts: 1467
Location: deep down in Florida...
I got both tubes from TC Tubes. The 50s RCA JRC 12AX7 label said it measured 1500/1500 Gm, but I have no idea what that means... all I know is that it's a great sounding tube.

The 50s Sylvania 12AX7 BP also measured 1500/1500. It is a cleaner sounding tube, not as much gain as the RCA, but it felt low on output.

Both were very quiet tubes. I have a couple more BP tubes on the way, Raytheon and Tung-Sol 12AX7.

I'm still digging the GL 12AX7, it has most of the characteristics I'm looking for in a preamp tube. It works great when I'm playing a Strat, straight through with the amp volume at 6. I don't like them as much with humbuckers, maybe a little too much gain, so I'm going to try to test the amps with something different while playing my 345... I seem to remember the Telefunken and Amperex I have were a better match for this guitar, smoother sounding in a way. I'm not as concerned about brightness and clarity when playing the 345, it's a completely different tone... but with a Strat I want that clarity and brightness and more of that "metallic" tone.


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Sun Apr 20, 2014 7:36 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Cedar, the "1500/1500" value is the trans-conductance or mutual conductance of the tube tested. Mutual conductance is a measure of how well the tube passes current with the change in signal grid voltage. Or the measure of the relative amplification of the signal, as a function of the signal voltage (AC) "swing."

In math terms = (change in current) divided by (change in voltage).

From Ohm's Law, I/E = 1/R.

That is why the value is in micromhos. "mho" = ohm in reverse (or inverse of resistance).

"Micro" = 1 millionth of a mho.

For 12AX7 type tubes, 1500 umhos reading is a healthy tube with good mutual transconductance or amplification. 1000 umhos is borderline (around 66% of a good tube's MT). Many very good NOS 12AX7 tubes test around 1800-2000 on my Hickok.

There are two numbers: 1500/1500, for the 12AX7 you posted because there are two triode sections in this tube. These numbers indicate the balance of the tube’s sections.

IME, it doesn't matter whether you are testing a Raytheon, Telefunken, RCA, etc. 12AX7/ECC83 --- if the tube tests at or below 1200/1200, it is not going to sound very good in a Fender amp. This is true for most any guitar amp. Because, guitar amps usually place the 12AX7 into a very high gain environment (plate voltage, idle bias, and signal strength). Much higher that most hi-fi amps. You need a strong tube, which is quiet, for these sections.


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Sun Apr 20, 2014 7:57 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26415
Location: Tombstone Territory
BMW2002Ti wrote:
Because, guitar amps usually place the 12AX7 into a very high gain environment (plate voltage, idle bias, and signal strength). Much higher that most hi-fi amps. You need a strong tube, which is quiet, for these sections.


+1

Which is why Leo specified the then-new 7025 with its spiral-wound heater element for use in the V1 and V2 positions of his amps -- similar gain coefficient and curve as with a 12AX7 but with a better noise floor to provide a superior S/N ratio.

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Sun Apr 20, 2014 8:52 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Sat May 22, 2010 10:53 pm
Posts: 1467
Location: deep down in Florida...
Thanks for the lesson! The problem I have with the numbers that come with tubes is that they vary and I really have no clue what the differences are... I just go for the ones that are listed as strong or "NOS", but that's not always a guarantee it's gonna sound good in my amps.

BTW I have 4 Telefunken 12AX7, 3 smooth plates and one ribbed. The ribbed one is noisy, not microphonic just noisy and crackles... earlier today I loaded all 3 smooth plates in my VLR, V1/V2/V4, and that combination worked really well with my 345. With the amp dimed the Telefunken did a much better job keeping it together compared to the GL. At loud volumes and with humbuckers the GL got a little messy, too much gain I guess. They work much better with a Strat IMO.


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Sun Apr 20, 2014 9:24 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
cedarblues wrote:
Strong or "NOS", but that's not always a guarantee it's gonna sound good in my amps.

BTW I have 4 Telefunken 12AX7, 3 smooth plates and one ribbed. The ribbed one is noisy, not microphonic just noisy and crackles... earlier today I loaded all 3 smooth plates in my VLR, V1/V2/V4, and that combination worked really well with my 345. With the amp dimed the Telefunken did a much better job keeping it together compared to the GL. At loud volumes and with humbuckers the GL got a little messy, too much gain I guess. They work much better with a Strat IMO.


Most Russian and Chinese tubes are based on military applications. And do not fully follow the design path of audio tubes. So, ultimate headroom (which is lacking in the GL, but is in spades with the TFK) is a consequence of adaptation to audio use.

To gain clean headroom, try a 5751. The 5751 originally was a mil spec tube (in the 1950's), for military apps. But, is reknown for its headroom. Purely serendipity (bet you'd never see that word in a guitar amp thread :lol: ). A good 5751 will give you very clean high notes and bass. Tad less mu, but rich harmonic midrange character. Best one? IMHO, the Raytheon windmill getter. Followed by the gold labeled Sylvania CHS-JAN (not JHS-JAN) black plate.

Forget the new issues. They lack the clean, clear, high-end shimmer you seek.

Good luck! Keep us posted.


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Sun Apr 20, 2014 10:35 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26415
Location: Tombstone Territory
BMW2002Ti wrote:
A good 5751 will give you very clean high notes and bass. Tad less mu, but rich harmonic midrange character. Best one? IMHO, the Raytheon windmill getter. Followed by the gold labeled Sylvania CHS-JAN (not JHS-JAN) black plate.


+1

I have a couple of sleeves of GE-made JAN's that also sound very mellow and articulate (one set manufactured in '58, the other in '61). They sound best in a brownface and certain tweed models.

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Mon Apr 21, 2014 7:09 am
Offline
Professional Musician
Professional Musician
User avatar

Joined: Sat May 22, 2010 10:53 pm
Posts: 1467
Location: deep down in Florida...
The GL did some wonderful things to my amps, but I have to admit, it's only good up to a certain point... for most folks it's probably OK, as long as you keep the volume around 6 or lower. I don't use any pedals to drive the amp, so with a Strat plugged straight in and the volume around 6 it's heavenly!

The only 5751 I tried is a JAN Philips from the 80s. I didn't really care for the tone, but it's been a while since I tried it, I could give it another try... might also have to try some of the ones you've recommended.


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Mon Apr 21, 2014 7:24 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
cedarblues wrote:
Then I'll stick to the way I've been doing it...

No Psvane yet, but I did get these two...

Image

Image

Just tried both real quick, nice clean sounding, prefer the RCA... I'm glad I found another NOS that sounds great! The Sylvania is nice, but seems a bit low on output, but I like the clean tone.


Cedar, these are very early 12AX7's (late 1940's-early 50's). And although RCA was the first to design and place them into their receiving tube manual, RCA did not manufacture them until the 1950's. I would not be surprised if Sylvania (they look like the late 1940's square getter, BP's) or GE actually made those tubes.

All of the early RCA made 12AX7's I seen had "D-shaped" getter rings.


RCA 12AX7 with D-getter ring:

https://www.tubeworld.com/12ax7rcablack50s.jpg

Sylvania made 12AX7 with square getter ring:

https://sp1.yimg.com/ib/th?id=HN.607990 ... 7&pid=15.1


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Mon Apr 21, 2014 7:47 am
Offline
Professional Musician
Professional Musician
User avatar

Joined: Sat May 22, 2010 10:53 pm
Posts: 1467
Location: deep down in Florida...
TC Tubes had them listed as 50's mil spec RCA JRC 12AX7. Here's some closeup pics of the getter

Image

Image

Image


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Mon Apr 21, 2014 7:55 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Yup... those are RCA made D-getter ring 12AX7. These early production 12AX7's are very good tubes. Whether made by RCA, Sylvania, or GE. They last forever.

Good pickins! :D


Top
Profile
Post subject: Re: 12AX7/7025 Tubes
Posted: Mon Apr 21, 2014 8:09 am
Offline
Professional Musician
Professional Musician
User avatar

Joined: Sat May 22, 2010 10:53 pm
Posts: 1467
Location: deep down in Florida...
It's a great sounding tube for sure! Clean and clear sounding with just the right amount of gain...


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 143 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6, 7 ... 10  Next
Go to page Previous  1, 2, 3, 4, 5, 6, 7 ... 10  Next

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: