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Post subject: Used Blues Deville 410 with unknown mods
Posted: Thu Dec 09, 2010 4:54 pm
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Let me start by saying I just discovered this forum a few days ago and am astounded at the wealth of info here.
Now on to the issue, I recently traded for a used Blues Deville 410 Reissue and it has never seemed to get very loud o me on the clean channel without getting kind of crunchy. My Peavey Classic 50 gets much louder without breaking up at all. I did a bunch of tube swapping and even ran another preamp into the return on the Deville which got very loud and clean. I finally decided to pop the back and take a look and found what looks to me like two resistors added to the top of the tube socket board. I'm hoping someone here might be able to help figure out what these are doing. One is on top of the preamp tube closest to the power tubes and one is near the end of the board near the power tubes. Big pictures can be seen here. [http://gallery.me.com/bonind#100329]

Please excuse me if my image or URL don't post properly, it's my first post!Image[/img][/url]


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Posted: Thu Dec 09, 2010 4:59 pm
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We should see some pictures to help you.


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Posted: Thu Dec 09, 2010 7:25 pm
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Hi dbow,

This picture shows the location of the test point for checking the bias (link below). Looks like a resistor was added in parallel to the one underneath (the square white one) , not sure why. Originally, the resistor underneath is a one ohm resistor, the only function is a test point. There is no reason to add a resistor here, unless there wasn't one there to begin with (I believe that there was one there already), but still no reason for the one on top to be added, and that alone would make me want to take it back. It doesn't even look like a good solder job, yuck! It is possible that if the resistance of the one underneath were changed to a high enough value, it would limit the current going to the output tubes to reduce the power output. Again, why would anyone do that? You can put in 6V6 tubes to reduce power without hacking up the circuit. The bias pot itself has been adjusted, looks like it is fully clockwise, which would be biased hot....which again makes no sense, especially considering the other mods.

http://gallery.me.com/bonind#100329/IMG_0928_2&bgcolor=black

This second picture (link below), not only shows the resistor added on the board in the middle of the picture (can't tell where it's connected), you can also see circuit modification in the upper left (R77) which is a resistor in the bias supply circuit. R83, also in the bias circuit is also removed/moved. The amp already has an adjustable bias(blue pot at top of picture), so there would be no reason to change this circuit, except maybe to compensate for the other changes made. It is hard to tell where exactly the resistor in the middle of the picture was added in the circuit, so it's hard to say why it was added, but it too looks a little sloppy.

http://gallery.me.com/bonind#100329/IMG_0926&bgcolor=black

Maybe you could ask the person that you got it from, exactly what was the goal of the circuit mods. You could reverse the changes maybe, but I would return it if you could. I would be wary of even playing it, for fear of something failing and ruining the tubes. I would have to have a closer look at the amp itself to try and determine what the mods are for, but it appears that the modder was possibly trying to modify the amount of power out of the amp. On the other hand, the speakers in it look like some kind of old speakers that might be cool, they definitely are not stock. Hope this helps a little. :idea:

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Posted: Thu Dec 09, 2010 8:58 pm
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Thanks for all the info Shimmilou! Unfortunately the amp is mine now and there is no way for me to contact the previous owner. I have put about twenty hours on it without any problems and it definitely seems to run cool. My gut reaction when I saw those resistors was to just clip them but I'm a bit scared to do that.
I'm in a pretty small town and our one good amp guy passed away or I would have him restore it to stock.
I thought the speakers were stock, they do not look old/vintage to me. I think they are powdercoated. I put a couple of pictures on the gallery, http://gallery.me.com/bonind#100329, now I'm curious what they are.

Thanks again for all the info.


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Posted: Thu Dec 09, 2010 10:10 pm
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Yeah, there might be some other changes that aren't apparent and cutting out the resistors may disable the amp, or worse. I say that the speakers aren't original, looks like the seal on the screws is gone, indicating that the screws have been removed at one time.

But, without being able to see for sure where these resistors are connected, it is just guess work as to what they are for. The only mod that I can tell for sure, is that the bias circuit has been changed. The resistance at R77 was decreased, and if I'm thinking correctly that would make the bias hotter (less negative voltage), and also the pot cranked making it even hotter, but you say it is running cool, so I don't know. :?

Do you have the schematic, and can you read it? The schematic on the Fender site seems to be for the original version, and I think that the newer amps are different than that schematic. The fact that yours has the adjustable bias pot, leads me to believe that you have a newer version. If that's the case, the schematic for the Hot Rod Deville may be closer to what you have if yours is a newer version. Any idea of how old the amp is, MIM or MIA?

If no one else answers about your speakers here, maybe you could make another topic asking about the speakers (show the pictures), I don't know much about them. :idea:

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Posted: Fri Dec 10, 2010 3:20 am
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dbow,


Don't cut the resistors

All shimmilou said make sense. And thank shimmilou for the pictures, with your post is the only way for me to see them.

I can't find myself the good version of shematic, the only one I find is a blues Deville without bias pot and not the same resitors number.
And without layout, hard to identify which resistor is.

But IMO the solders where not bad , It's is not easy to make solder look good on printed circuit but almost the time they make the job.

If the amp work fine and you like it, tell yoursef that everything ok.

The resistor R77 on the bias circuit ( I assume shimmilou is right) could be there to have more negative bias voltage, and the pot is turn the side to be hot to have the good voltage with the new resistor.

It is good to check used amp after buying, but don't forget " if it work,don't fix it"


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Posted: Fri Dec 10, 2010 3:59 am
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I find the right schematic : Hot Rod Deluxe

On the schematic, bias pot turn clockwise is for cold bias.

I assume shimmilou is right for locate resistors:

If R77 is smaller ( with other one in parallele) bias voltage is low so you have to turn pot clockwise to have the proper negative bias voltage. Pot look almost full clockwise on the picture: good.

The resistor (1 ohms ? for mesuring bias ) close to one 6L6 and near the 5 watts square cement resistor... I don't see 5 watts resistor ond schematic, they write 1 watts !! Did they use 5 watts in place ?


I have the same conclusion : leave the amp like that


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Posted: Fri Dec 10, 2010 7:49 am
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Hi stratele52,

Good suggestions, thanks for the input. Yeah, the mod to the bias circuit is confusing, the poster says that the amp is running cool. If you look at the schematic for the HRDvl, making R77 smaller value will be less negative bias voltage, more idle watts, and turning the pot clockwise (CW closer to ground potential) is also less negative bias voltage, more idle watts. So the combination of the two things would be very low negative bias volts, very high idle watts. Am I seeing that correctly? (note that at the bias pot CW --> points toward ground, less negative volts, higher idle watts)

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Posted: Fri Dec 10, 2010 9:02 am
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Guys,

The correct block diagram is on page 11:

http://www.blueguitar.org/new/schem/fen ... eissue.pdf

PCB layout is on page 14.

It is applicable to both the Blues Deluxe Reissue and the Blues Deville Reissue.

Don't use a Hot Rod Deluxe/Deville block diagram.

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Posted: Fri Dec 10, 2010 9:52 am
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Thanks bluesky636 for the link (yet again). :lol: This time I bookmarked your link, instead of just downloading it. :)

I was comparing the manual/schematic you provided to me before, and the HRDvl schematic, and that section of the power supply is identical, so we can use it. Definitely better to have that manual and schematic. What do you think, am I seeing the circuit operation right? Lowering the resistance of R77, and/or turning the bias pot CW (note the CW and arrow on schematic points to ground), would give less negative volts, allowing more idle watts. Correct?

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Posted: Fri Dec 10, 2010 10:44 am
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shimmilou wrote:
Thanks bluesky636 for the link (yet again). :lol: This time I bookmarked your link, instead of just downloading it. :)

I was comparing the manual/schematic you provided to me before, and the HRDvl schematic, and that section of the power supply is identical, so we can use it. Definitely better to have that manual and schematic. What do you think, am I seeing the circuit operation right? Lowering the resistance of R77, and/or turning the bias pot CW (note the CW and arrow on schematic points to ground), would give less negative volts, allowing more idle watts. Correct?


I'm not sure what is going on.

I think the bias pot has been turned counter clockwise, not clockwise. If you look at the red glyptol (or what ever Fender uses to hold the pot dial in place) on the pot face and body, the red area would be pointing straight down on the pot a the factory bias setting (that's how it was on my BDRI). If the pot were turned clockwise, the red area would be at the left side of the pot. That is where mine is now. For the red area to be on the right, as shown in the photos, would require the pot to be turned counter clockwise.

The resistor that is soldered to the tube PCB looks like it is in parallel with C25 or maybe R58?

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Posted: Fri Dec 10, 2010 11:10 am
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So the combination of the two things would be very low negative bias volts, very high idle watts. Am I seeing that correctly? (note that at the bias pot CW --> points toward ground, less negative volts, higher idle watts)
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Posted: Fri Dec 10, 2010 11:29 am
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Hmmm, that's interesting bluesky636. I had not considered that the pot was turned CCW, could be. That would be counter to the effect of the lowered resistance of R77....so, interesting still. Yeah, I was thinking that the resistor added by itself on the tube socket board was in the area of the plate resistors for the preamp tubes, but who knows what is going on here. :lol:

No problem stratele52, I have some dyslexic spells myself, usually with capacitors, I can understand. :wink: Yes, when you first look at the pot (on schematic), it does look like turning it up would be towards the supply. :lol:

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