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Post subject: 12AX7 substitutions in a Champ
Posted: Fri Dec 18, 2015 9:42 am
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I am having a blast with my newly assembled 5F2A and would like to experiment with slight tone changes to see what it is capable of and have a tube question.

Currently, I have all RCA NOS tubes including the 12AX7. Would there be any harm in trying 12A* variations? I found this and of course the tone nut me would like to try one or two and found this.

Quote:

What is the difference between a 12AX7 and a 12AX7A?
ANSWER - Back in the Old Days the "A" was Used to Designate the Tube as LOW NOISE. With Modern 12AX7's it Makes No Difference at All.

What is the difference between a 12AX7A and a Chinese 12AX7B?
ANSWER - The Chinese 12AX7B tube has a higher gain and a little more overdrive than the standard 12AX7A tube. It also is a quieter and Warmer sounding tube. It is a good tube to use for higher gain guitar amplifiers. If you want to upgrade, go with a 7025 tube or a Good Ol' NOS Telefunken, Buble Boy, Valvo or RCA 12AX7.

What is the difference between a 12AX7 and 7025?
ANSWER - The 7025 vacuum tube is basically a 12AX7 with Lower microphonics and Lower Hum. It is a much quieter sounding tube as far as tube noise is concerned.
12AT7 * * * * The 12AT7 is a clearer sounding tube than a 12AX7 but with a little less gain.

12AU7 * * * * The 12AU7 sounds like a 12AX7 but produces a lot less gain in the preamp circuit. Arguably the Best sounding American 12AU7's ever made are the RCA Clear Tops and Tung-Sol's.

12AY7 * * * * The 12AY7 sounds warmer with more bottom end to it than a 12AX7.

5751 * * * * The 5751 sounds smooth with nice mid range tones. It is warmer with good bottom end to it.

7025 * * * * The 7025 has a higher gain than a 12AX7 tube. It is also a crisper sounding tube. This is the industrial version of the 12AX7. You can beat the crap out of it and it will still go!



It's unlikely that I would ditch the RCA 12AX7 but I would like to try an RCA 12AY7 as long as it doesn't cause a problem. Is it safe to try other 12's in this amp.

Thanks,
Randy


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Post subject: Re: 12AX7 substitutions in a Champ
Posted: Fri Dec 18, 2015 10:30 am
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Trying a 12AY7 (or mil spec 6072) will not harm the amp. I like the GE 6072A. RCA makes a fine 12AY7. Their 7025 is one of the best 12AX7 type made (gray or black plates).

AFAIK, the Chinese 12AX7B does NOT have higher mu than a standard 12AX7.

The 7025 has a spiral-wound internal heater line, to help cancel 60Hz hum.

So does the original US made 12AX7A. Raytheon, Tungsol (USA), RCA, Sylvania, & GE made 12AX7A. "7025" is the mil spec designation. AFAIK, no difference between these two, in terms of structure and materials used.

5751 is a mil spec, lower mu (70 versus 100) version of the 12AX7. Triple mica, black plate versions being the most sought after. All US companies made dual mica and triple mica versions of the 5751. I like TMBP Sylvania 5751 tubes. And the Raytheon DMBP 5751 'windmill' and D-getter tubes.

How each 12A(_)7 variant sounds in your amp, is amp and listener dependent. You need to try each type in your amp, with your guitars, your pedals, and your ears --- to determine which is best.

Most ppl find the 5751 and 12AT7 (mil spec 6201 or 12AT7WA) the best subs in their amps. 12AY7 in amps with a too much gain in the input section (too hot sounding). The 12AU7 type is not a very musical tube (IME). Best used in high gain amps, in the phase inverter section.

Of course YMMV. And what sounds good to me, may not sound so great to you.

:D


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Post subject: Re: 12AX7 substitutions in a Champ
Posted: Fri Dec 18, 2015 3:14 pm
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You can safely put any 12XX7 tube


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Post subject: Re: 12AX7 substitutions in a Champ
Posted: Sun Dec 20, 2015 2:17 pm
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stratele52 wrote:
You can safely put any 12XX7 tube


I would add the caveat that a 12ATY consumes significantly more heater current than other dual triode types. When using this tube in your Champ's V1 socket, be sure to monitor the power supply for overload indications. If your T1 tranny is a quality type (Heyboer, Hammond, Merc-Mag, etc) you shouldn't have any problems.

That said, I think you'll find the best results with a 12AY7 or a 5751.

Arjay

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Post subject: Re: 12AX7 substitutions in a Champ
Posted: Sun Dec 20, 2015 2:41 pm
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Retroverbial wrote:
stratele52 wrote:
You can safely put any 12XX7 tube


I would add the caveat that a 12ATY consumes significantly more heater current than other dual triode types.


Arjay


I talk about 12XX7 tubes , 12ATY is not one of those . :lol:

If you mean 12AT7 , in my RCA Tube Book , it need 0.3 amp like a 12AX7


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Post subject: Re: 12AX7 substitutions in a Champ
Posted: Mon Dec 21, 2015 2:17 am
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Duh, my bad!

You are correct, mon amí.

:oops:

Arjay

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Post subject: Re: 12AX7 substitutions in a Champ
Posted: Mon Dec 21, 2015 2:24 am
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Retroverbial wrote:
Duh, my bad!

You are correct, mon amí.

:oops:

:lol:

Arjay


Joyeux Noël mon ami :D


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Post subject: Re: 12AX7 substitutions in a Champ
Posted: Tue Dec 22, 2015 5:22 am
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I have used a 5751 in nearly every fender amp I've owned for the first stage of gain in what ever channel I use the most or in the case of single preamp tube amps like a champ I use them as the only preamp tube.
I found that the 5751 smooths out the preamp while allowing the power tubes to do what they do best.

I keep a stash on hand at all times ! 8)

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Post subject: Re: 12AX7 substitutions in a Champ
Posted: Tue Dec 22, 2015 10:06 pm
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Just bought an old JAN 5751 SYLVANIA that supposedly tested NOS. I don't put a lot of trust in the reported test results but that's all I have to go on when buying old stock. My first "Tested Strong" 12AX7 was extremely microphonic and replaced with a spare 12AT7 - Raytheon or Sylvania I think. It's a mix of GE and RCA now and I've accumulated 3 times as many tubes as I can use and it's getting expensive, but I'm dialing in the tone which is what I planned on doing once the amp was assembled.

I'm sure all guitar players are tone nuts but I'm a total noob at this, and after hearing the subtle differences between tubes, even through a little Champ with 2-12's, I am surprised that anyone would buy new tubes. Dialing in the tone is part of the hunt.

I ordered a single 12" WGS G12Q 20 watter, which is at the bottom of the barrel in popularity from what I can tell, but the small Alnico magnet should respond well with the Champ's low output and break up early enough. I listened to Celestion, Jensen, Mojo, Weber and honestly liked the tone of the WGS as well or better - and I listened on and off for a week before deciding. All samples were through my PC with a decent 2.1 set of speakers but it will be about a week before I find out how much of a gamble this was. It won't stay around long if I don't like it.

Not mine but a sample of the G12Q

I've strayed far from my original post about wanting to build a true clone but what I really wanted was to get as close to the center of the ballpark as I could and and tune from there - make it mine if that makes sense. So far this has been an enjoyable\sometimes frustrating experience but I'm very happy with the progress.

You guys have been a huge help - especially Beemer for the step by step troubleshooting.


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Post subject: Re: 12AX7 substitutions in a Champ
Posted: Tue Dec 22, 2015 10:57 pm
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Be sure to give that WGS speaker 30 or 40 honest hours of break-in before rendering final judgment. Those that I've heard sound pretty sweet once they've had some "seasoning".

Arjay

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