Ryan
130 posts
Feb 08, 2010
12:34 PM
|
I'm wondering if you all can give me some suggestions/help in regards to changing the pre-amp tube on my amp. I don't know a whole lot about electronics, but from what I've read, and the online videos I've seen, it seems that swapping the pre-amp tube is something that I should be able to do fairly easily without destroying my amp or killing myself.
It is a small 5 Watt amp, and it seems to be pretty similar to a Champ. It has a 12AX7 tube, and I think it sounds pretty good when I get the volume cranked up, and I really haven't been having feedback issues. But I think I'd like to put in a tube that has just a little less gain so that I can get a bit more overdrive, especially at lower volumes. I live in an apartment and when I practice I can't have the amp cranked up too loud, but then the amp sounds too clean.
I ussually prefer not to have a heavily distorted "Chicago sound", I prefer a cleaner sound with a little overdrive. So I don't think I want to use something with a really low gain like a 12AU7 because it will give more distortion than I like. So I'm thinking I should use something with just a little less gain. As I understand it, the 12AX7 is the highest followed by 5751, 12AT7, 12AY7(in that order).
So I'm thinking I should try out the 5751, or maybe the 12AT7. I know the 12AY7 is a popular choice and gets used in a lot of harp amps. But I'm thinking it might give me more overdrive than I'm looking for, considering the 12AX7 sounds pretty close to what I want(only when the volume is cranked up though). So what do you guys think? Should I try the 5751 or the 12AT7(or maybe even the 12AY7)?
I' ll have to check again, but if I remember correctly I don't think they're too expensive, so maybe I could buy a couple different ones to see what I like. Do you have any recommendations on which brand to get? I've heard the JJ Tesla tubes are pretty good. Thanks for the help.
|
barbequebob
447 posts
Feb 08, 2010
12:40 PM
|
A 5751 is somewhere inbetween a 12AX7 and 12AY7, and ther is some variance based on who makes them as there is with any tube, and certain tubes do sound better in certain amps than others (as it also does with certain brands as well).
I'll tell you what, if you have severe volume problems, I'd probably get my hands on an amp simulator that you can use with a set of headphones, like a V-Amp (best bang for the money overall) or a POD. They were originally designed to bypass amps entirely and used to record straight into the board and I know Magic Dick used one on his last recording with Jay Geils Bluestime.
----------
Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
|
Kingley
816 posts
Feb 08, 2010
12:41 PM
|
Ryan - Your thinking is a little confused. A 12AX7 will give you the most gain in any amp, a 12AY7 is lower gain and a 12AU7 is the lowest gain tube.
If you find you really need to crank your amp to get an overdriven sound, then it sounds as if your mic could be the culprit. If you are not using a Hi-Z mic then you'll need to use an impedance converter with the mic.
A champ style amp with a 12AX7 preamp tube and a bullet mic for example will begin to overdrive around 2-3 on the volume. With a 12AY7 it'll begin to overdrive around 4-5.
|
Kingley
817 posts
Feb 08, 2010
12:50 PM
|
I just reread my post and I forgot to explain that the higher gain the preamp tube is, the lower the feedback and overdrive thresholds of the amp are when using a mic.
So a 12AX7 will overdrive earlier and feedback more quickly than a 12AY7 for example. Of course there are other factors that can come into play as well.
If you're after more overdrive at lower volumes then BBQ Bobs suggestion is a great one. You could also try using an attenuator.
|
Ryan
131 posts
Feb 08, 2010
1:01 PM
|
So the lower gain tubes, such as the 12AU7, will give you less overdrive? And if you have one of the lower gain tubes you have to turn the volume up more in order to get overdrive?(like in your example, with the 12AX7 you will get overdrive at 2-3 on volume, but if you have the 12AY7 you need to have the volume up to 4-5 in order to get the same amount of overdrive).
That makes sense. I guess where I got confused is that I always heard people talking about swapping out the 12AX7, and I thought they did this with the intent of getting more overdrive/distortion. So are they switching them out so that they can turn the volume up louder with out getting too much distortion? If this is the case, then maybe I shouldn't swap out the 12AX7.
Last Edited by on Feb 08, 2010 1:04 PM
|
Kingley
818 posts
Feb 08, 2010
1:07 PM
|
You have basically the right idea Ryan. The reason that people swap out a 12X7 for a 12AY7 is to increase the headroom of the amp. What this means in English is that the amp can be turned up louder before feedback. Using a 12AY7 often also makes the amp sound a little warmer.
Are you using a mic with a volume control?
If so do you have the volume control on the mic on full?
If you have the mic volume on full (assuming it's a Hi-Z mic) then you will probably find you don't need to crank your amp to get overdrive using a 12AX7.
|
Randy G. Blues
160 posts
Feb 08, 2010
1:18 PM
|
I put this chart together a couple of years ago when trying to "calm down" my Genz Benz BP-30 for harp use. Please feel free to correct any mistakes, folks. I got this info from a few different websites, so before taking it as Gospel, research to be sure:
----TUBE ---------- % GAIN -----
12AX7/7025/CV4004 ---- 100
5751 ------------------ 70
12AT7 ----------------- 60
12AZ7 ----------------- 60
5965 ------------------ 47
6072/12AY7 ------------ 44
6829 ------------------ 39
12AV7 ---------------- 38-40
12AU7/6189/5814 ------ 17-20
Last Edited by on Feb 08, 2010 1:21 PM
|
Cisco
72 posts
Feb 08, 2010
1:22 PM
|
12AX7 - 100% gain
5751 - 70%
12AT7 - 60%
12AY7 - 45%
12AU7 - 19%
In my Fender 57 champ and Deluxe I use a 12AY7 for the first preamp tube.
|
Ryan
132 posts
Feb 08, 2010
1:44 PM
|
Okay, I think I've got it all straightened out. Although I wonder why I often hear people talking about wanting to get the "tone" that they like at lower volumes (this is ussually when talking about large 50watt amps), wouldn't they be able to accomplish this by putting in a higher gain pre-amp tube. They could always switch back when they know they're going to need more volume. Maybe it has to do with the other qualities of the lower gain tube(warmer sound, fewer feedback issues) that Kingley mentioned. Thanks for all the help, I appreciate it.
Last Edited by on Feb 08, 2010 2:20 PM
|
javajoe
68 posts
Feb 08, 2010
11:59 PM
|
As I understand it, the reason to swap to lower gain preamp tubes (5751 or 12AY7, for example) is for less gain in the front of the amp (preamp section) to allow pushing the power tubes (back end) harder before feedback. This allows for the more pleasing sound of power tube break up rather than preamp tube distortion. Isn't this usually done on larger amps (say, 50 watt) to allow for more breakup before feedback?
Last Edited by on Feb 09, 2010 12:01 AM
|
Bluefinger
57 posts
Feb 09, 2010
1:54 AM
|
javajoe,
yes, it's done especiall in larger amps with more gain stages. In a typical mid sized amp the signal runs through two gain stages and then the phase inverter. Especially in the first gain stage it makes sense to use a lower gain tube to fight feedback. You can also work with -fb and such. In an amp like the Champ you don't have too many choices because there is just one preamp tube and then the signal goes straight to the power tube ... no phase inverter, no tone stack, no -fb, no nothing. Nevertheless a 12AX7 in a single gain stage amp is still fine. Too little gain all together can often thin out the tone and make it sound weak. It all depends on personal taste, the mic used, the playing style and the rest of the amp configuration. It all comes down to buying a couple of tubes and trying them all. It's good to understand a bit of theory behind it but in the end you will have to buy a couple of different tubes and compare them.
----------
If it ain't broke you just haven't fixed it enough ...
|
Kingley
820 posts
Feb 09, 2010
2:34 AM
|
In amps with only one pre-amp tube I would only ever swap a 12AX7 for a 12AY7 or a 12AT7. These type of amps are generally referred to as "single ended" or "Class A" amps. Using a 12AU7 for example in a "Class A" amp would cut the gain too much and the amp will lose a lot of liveliness.
Some common mistakes that people new to amplified harp make are:
1. They use a Lo-Z mic then think the amp is rubbish because they have to crank it to get overdrive. All guitar/harp amps are Hi-Z inputs and therefore need either a Hi-Z mic or a Lo-Z mic with an impedance converter.
2. People use a mic with a volume control and think that turning the amp up full and the mic down is the way to get a good sound. The reality is this is the other way round.
3. People tend to crank the treble and middle to get a good sound then complain that they are getting lot of feedback. Generally when using a mic and amp, you need to set the tones lower with a slight bass boost to get the optimum sound. This is because of the sound frequencies generated by the harmonica. Of course this can vary from amp to amp but as a general guide it's the place to start when dialing in your sound.
4. A lot of beginners complain that the amp is feeding back and sounds thin and trebly. Often this is down to player technique. It's usually a combination of bad acoustic technique and mic cupping techniques. It can also include any of the things mentioned in points 1-3.
The main thing to remember is that using an amp is in some ways like playing a new instrument. For most people it will take lots patience and practice to get it to sound good.
|
walterharp
225 posts
Feb 09, 2010
8:53 AM
|
The way I like to think about it, for most amps, is that the tube-based overdriven sound related to the amp comes mostly from the preamp tube or tubes (you can get some distortion from speakers, and lots from cupping and overdriving a mic). Thus, if you want to get overdriven sound, then you need to hit the preamp tubes with a big signal. That would mean using a good hot microphone and getting your cupping down, or maybe a pedal that has some gain feature.
If you have a single tube amp, then lower gain tubes will not do much for you. If you are trying to tame a multi tube preamp section, by using lower gain tubes so that the volume knob turns farther and has a wider sweep before the feedback point, and still maintain tube distortion, the lower gain tubes should go later in the signal chain.
The reason I say that the power tubes are really hard to overdrive, is that in amps with a master volume you can crank down the volume at the preamp stage and bump up the master volume and get mainly a clean signal. Another way to think about this is that multi-channel amps with gain channels, have all the difference in gain and distortion and clean channels in the preamp section, the power tubes are driven the same on both channels.
|
Rick Davis
191 posts
Feb 09, 2010
9:21 AM
|
Ryan, in a low-power amp such as a Champ, using a 12AY7 tube in the preamp section will reduce it's volume quite dramatically. 44 percent of 5 watts ain't much. (2.2 watts!) A change in the signal at any stage affects the performance of all components down the signal stream.
I'd suggest trying the 5751 tube as well. You can get a very nice-sounding NOS JAN Philips 5751 from Tube Depot in Memphis (and at their website) for $20. With the 5751 your amp will still have some balls.
Ryan, is there a certain tone you are trying to emulate; a certain player?
----------
-Rick Davis
Blues Harp Amps Blog
Roadhouse Joe Blues Band
|
javajoe
70 posts
Feb 09, 2010
1:06 PM
|
I've owned 3 Champs... 2 Siverface (68 & 70) and a mint, 64 Blackface Vibro Champ. The 5751 was THE preamp tube for all three. One SF had the negative feedback resistor replaced which mad it much more dynamic sounding and a Weber speaker replacement... Ceramic, I believe it was.
The 12AT7 preamp tube is NOT a good option... It is designed for phase inverters, I believe.
To my ear, Walterharp, there is conciderable difference between preamp tube distortion, power tube distortion, and speaker breakup.
I prefer the latter 2 for the 'Chicago' sound.
|
markdc70
19 posts
Feb 09, 2010
1:59 PM
|
A common misconception with swapping preamp tubes is that with lower gain tubes you can "turn the amp up louder before feedback". What is actually happening is that you are just having to turn the volume pot up higher to get to the same volume, your amp does not get any louder before feedback. The tone changes come from the tube drawing more or less current and therefore ending up being biased differently. Go to the amp forum on lonewolfblues.com and you can learn anything you ever wanted to know about harp amps!
|
Ryan
147 posts
Feb 11, 2010
9:40 AM
|
"Ryan, is there a certain tone you are trying to emulate; a certain player? "
Well personally I don't ussually like to have that heavily distorted Chicago tone. Ideally I prefer a cleaner sound with just a bit of overdrive. I don't want it to be completely clean or I'd just play through a PA. I'm not sure if there is one particular player I can name that I'd like to emulate exactly, but I like Jason's sound. Although I also like the tone that Sugar Blue sometimes uses(maybe I'd like a little less overdrive than he uses though). I know these two have very different sounds, so maybe I'm not making any sense. I guess I'm pretty bad at describing the type of tone I prefer. I like different sounds for different situations.
I suppose I'll just have to buy a few different tubes and experiment.
EDIT: Now that I've had this amp for a few days and have spent more time playing it(it was brand new and never been played before), I've noticed that it's reacting differently and sounding better at lower volumes. But I'd still like to get some different tubes to try out, so that I can have it sound the way I want at louder volumes as well. Maybe it needed to be broken in a bit, or maybe I'm just crazy.
Last Edited by on Feb 11, 2010 10:18 AM
|
