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Posted: Tue Nov 09, 2010 12:56 am
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Man, that's cool ! And you've got a nice touch on the geeetar ! Art

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Posted: Sat Nov 13, 2010 11:13 pm
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After completing this project, I think I found a flaw in the Blues Deluxe output transformer wiring. On my amp, 1995 USA model, the output transformer primary blue wire is on CP1 and the brown is on CP2. These should be reversed. The blue wire should be on the power tube farthest from the p/i (CP2 according to the schematic) and the brown should be on CP1. Any brave soul willing to switch them for the cause? Can't promise you your amp won't burst into flames. This will probably lower the volume and change the tone a little also, because I don't believe the feedback loop is working properly as it is. I discovered this toward the end of my conversion to turret board and would have tried it myself, but cannot now because of the new innards.


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Posted: Sun Nov 14, 2010 1:00 am
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Perhaps the BD schematic is in error......?

That's a tough call to make, rjake.

Good catch though -- I'm sure somebody will chime in with an informed opinion.

Arjay

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Posted: Sun Nov 14, 2010 1:22 am
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I verified it on the tube board I took out that CP1 is indeed located by the tube closest to the p/i, which is incorrect for the blue wire. The HRD appears to have the OT correct. I found this out when I wired it up with the turret board I built. That is why I had a high pitched noise in the presence control when turning it down. After switching the wires around, the problem was solved. The tone controls started working better also. I wonder if they fixed it on the reissue? That could be the reason why that amp never sounded as good as it should have.


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Posted: Sun Nov 14, 2010 2:26 am
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After checking out several schematics on various Fender amps, the blue and brown OT wires are not consistent on where they go. I need to do more research and testing it seems. One thing is for certain, when the OT is wired directly to the tube plates with the 5E5-A board and its feedback, it is not the same as the BD wiring. I still think the OT on the BD is wired backwards though, at least my '95 amp was, and the schematic is verifying it. After correcting the wiring with the 5E5-A turret board, it sounds great with more control over the tone and volume. The distortion is fantastic when cranked, only a little tighter with the power tube cap change. (.1 to .047uf)


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Posted: Sun Nov 14, 2010 5:56 pm
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Rjake, it doesn't matter what color the plate leads are. And I've seen this on a lot of amps. The OT primary will work in one way only. When these leads are swapped, there will be a reverse drive condition. this usually causes a loud howl or a high frequency squeal. This is a common thing when replacing the OT or the phase inverter circuit. When building an amp it's a 50-50 chance of getting it right. You just got it right the first time ! Art

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Posted: Sun Nov 14, 2010 6:51 pm
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Actually Art, I got it wrong. Originally, I did get what you described, until I moved the presence control ground wire. The amp still played with some squeal only when the presence and treble was turned down. The amp was louder and had heavy bass and ice-pick treble, like the Blues Deluxe. When I swapped the plate wires, everything started working properly, ie: tone controls, more control of the volume and a flatter frequency response. I attribute this to the feedback working correctly. All I know is, when the plate wires were landed on the tubes the same way they were on the Blues Deluxe, my 5E5-A amp didn't work correctly even though I had sound. After swapping the wires, the amp is working correctly and it sounds fantastic.


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Posted: Sun Nov 14, 2010 8:11 pm
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I do recollect you mentioning that, rjake. And I was at a loss to understand what might be causing those symptoms. But you stuck with it and finally tracked it to ground with a definitive diagnosis. What a great call! Be sure to document those transposed OT leads so that others who follow your footsteps avoid the same pitfall.

You've got one fine amp now.

Arjay

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Posted: Sun Nov 14, 2010 9:03 pm
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Thanks Arjay. Now if I can just get a Blues Deluxe owner to swap those plate wires on CP1 and CP2 to prove or disprove my theory, I"ll be content. :D

Art, do you think it would damage the amp if someone swapped the OT primary plate wires on a Blues Deluxe?


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Posted: Sun Nov 14, 2010 9:55 pm
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Have you taken that new amp to band rehearsal or an open-mic jam yet?

I'm curious about how it performs under field conditions.

Arjay

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Posted: Sun Nov 14, 2010 10:24 pm
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Not sure if it's a good idea, on the newer amp's OT. IMO The color coding on the OT is random because there is no way for the trans builder to know how the phase inverter is wired. I mean that you could keep the plate leads in line with a schem, but the PI may have to be reversed. It's good that you didn't mis diagnose the squeal. A lot of techs head for the NFB circuit whenever there's a high frequency squeal, and for good reason. But it's interesting that this symptom has changed it's sound, must be the components and trans interaction. Art

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Posted: Sun Nov 14, 2010 10:29 pm
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Quote:
Have you taken that new amp to band rehearsal or an open-mic jam yet?

I'm curious about how it performs under field conditions.

Arjay


Next weekend for sure. I don't play in a band anymore, but the old bandmates are waiting to hear it. I did put it through different tube swapping and worked the controls 1-12 this weekend. It sounds best with 12AY7(EH)-12AT7(RCA)- 12AX7(EH)-6L6EH-6L6EH. I use that RCA 12AT7 instead of a 12AX7 in the cathode follower socket because when overdriven, I get less preamp distortion and more power amp distortion, I think. Anyway, it seems smoother and more balanced.


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Posted: Sun Nov 14, 2010 11:03 pm
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A lot of techs head for the NFB circuit whenever there's a high frequency squeal, and for good reason. But it's interesting that this symptom has changed it's sound, must be the components and trans interaction. Art


I did clip the feedback to see if it stopped, and it did. It wasn't the feedback circuit itself, but the phase of the OT, I guess. Since the feedback circuit is taken off the OT secondary, it makes sense to me. There are probably alot of variables involved as to why this 5E5-A amp works with the OT primary both directions, ground buss I used, isolation of input and output jacks, re-use of BD components, etc. I'm not an amp pro and I don't have an engineering degree, just 25 years in various electronic fields troubleshooting. Guitar amps are just a hobby, but I do like to play guitar and always like a challenge.


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Posted: Sun Nov 14, 2010 11:21 pm
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I've been field-testing a pair of those EHX 6L6's in a '66 Bandmaster, biased at around 36mA. They've been in the amp for about a year now and they sound pretty righteous. Will advise as more data is collected.

Arjay

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Posted: Mon Nov 15, 2010 10:17 pm
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Rjake, I see what you're saying about the production amps possibly being out of phase, from the factory. I wasn't getting the gist of your theory, I was just thinking about a single amp. Yeah, why not try that on any amp with a squeal. Don't know who builds the current Fender transformers. But it could be a generic brand used in many brands of amps, thus the color code difference. You are quite right about it working in or out of phase, the older amps would howl like pained dogs(very big dogs), but the newer amps react with that high squeal. Very interesting ! You'd think that it would be the QC testing dept's job to check this in every amp it ships. I mean, they must have some massive device that checks all of the operating systems. Art

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