gmacleod15
9 posts
Sep 23, 2009
6:05 PM
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I was surfing for information on replacing tubes and found the following info on Billm mods website (site for Fender Blues Jr amps modifications).
Has anybody tried using a 12DW7 tube in their FBJr...or maybe some other none stock tube? I ordered one and will try it?
"Harp (harmonica) players may get a kick out of using a 12DW7, also known as an ECC832, in V3. This is a hybrid tube that has the gain of a 12AX7 on one side and the gain of a 12AU7 on the other. It drives the output tubes unequally, which causes distortion pretty much all the time. This can be good for harp, because you generally want to drive the amp into distortion to get your blues tone, but don’t want to play loud enough to cause feedback into the microphone."
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Jim Rumbaugh
88 posts
Sep 23, 2009
6:58 PM
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I say try it with caution.
There is distortion, and there is distortion. That's why some amps sound better than other.
Back in my youth when I recieved my electronics training I was taught, symetrical wave forms equal even numbered harmonics which equal pleasant tone. Uneven wave forms yeild odd order harmonics which equal harsh tone.
In theory (and I'm sure this can be debated) a push-pull amp output (2 tube, "class B amp")driven to overdrive should have a god tone. A single tube output tube ("class A output") would be more subject to an uneven output, therefore more prone to a harsh tone. That is why I believe the amps with 2 6V6 or 6L6 tubes in the output sound so good. To contradict what I just said, I'm sure there are some lower power amps with only a single tube out put where people "love the tone", but I am pesimestic that you will be happy with the 12DW7 experiment.
Last Edited by on Sep 23, 2009 6:59 PM
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Bluzdude46
200 posts
Sep 23, 2009
10:36 PM
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When I was researching tubes for my Epi Vjr project and then later The Bogen and The Bassman LTD. The conversation on the 12DW7 came up in one of the electronic geek rooms I cruise for info and I can't find it now but the conclusion as I best remember it was that the 12DW7 was a less natural sounding break up because as you say it's designed to do that and it really had no limits and would keep on distorting more and more as you crank up the gain. The result while interesting for guitar is probably overkill for harp. I remember classifying it in my "Good for guitar, Bad for Harp" category.
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harmonicanick
383 posts
Sep 24, 2009
1:16 AM
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@gmacleod15
I changed the pre-amp tubes in my BJ as follows with very good results:
Valve 1 - 12AU7
V2 - 12AU7
V3 - 12AT7
Settings I find work best are:
Reverb 0
Master 6-8
Middle 0
Bass 10
treble 3
pre-amp vol 6
No feedback now!!
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gmacleod15
10 posts
Sep 25, 2009
9:45 AM
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Thanks all for the comments. I'll post my opinion of the 12DW7 after I try it.
@harmonicanick
What mic do you use with those settings on your BJ?
G
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harmonicanick
385 posts
Sep 25, 2009
10:09 AM
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@gmc
an old green bullet mate
You could turn the middle up to 6 for a less bluesy sound, with it off its a chicago sound
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walterharp
68 posts
Sep 25, 2009
10:52 AM
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I would also try using higher gain tubes in v1 and v2, you get to feedback earlier on the volume dial, but you might get more usable volume and tone out of it. The thing to do would be to record with the 12au's in, then record again with 2 12 ax's turned up to right before feedback and see which level is higher and which tone is better side to side. the volume knob is not comparable across setups when different gain tubes are in the pre amp section
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gmacleod15
11 posts
Oct 07, 2009
6:20 PM
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I finally got to try using the 12DW7 tube as described in the initial post, and as some of you have already commented, the tone sounded harsh. I didn't like it.... oh well I have spent ten bucks in worse ways.
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