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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Wed Nov 21, 2012 10:00 am
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How the quality of these amps? noticed the mdf construction it would of been nice if it was birch ply:)


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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Wed Nov 21, 2012 10:58 am
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ken361 wrote:
How the quality of these amps? noticed the mdf construction it would of been nice if it was birch ply:)


Did you not read my first post: "The changes that I have made were not the result of a general dissatisfaction with the amp, but were out of a desire to learn more about tube amps (it was my first tube amp) and how they worked."

They are excellent amps in my opinion. I will talk about the cabinet construction in a later post.

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Wed Nov 21, 2012 11:02 am
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Before I get into component and circuit mods to the BDRI, it would be helpful to review the schematic diagram if you are not familiar with it. I'll be referring to it often.

http://support.fender.com/schematics/gu ... _Rev-A.pdf

Also, here is the service manual with parts list and component locations.

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

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Thu Nov 22, 2012 8:04 am
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Aspiring Musician
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Quote:
By this time I had learned about the real "tweed" amps from the 50's. Hey, the BDRI looks like a tweed amp. Can it be made to sound like one? Well, no. But I did learn that several tweed amps used a 12AY7 (gain factor of about 40 - 45) in V1. Why not. First I tried a EH 12AY7. I was not impressed. Then I said to myself "The 5751 is an NOS JAN tube. Maybe an NOS JAN 12AY7 would sound better". So, back to Mike K I went for some NOS JAN 12AY7s. Now my amp looked like this:

V1 = 12AY7
V2 = 12AX7
V3 = 12AX7
V4/V5 = 6L6GC


I really like my Blues Deluxe and it is one of my go to amps when I get creative. I think I am going to do the above tube swap, which ones did you get from KCA...
I did the C-Rex speaker about a year ago, big difference. I put the stock speaker in a 1 x 12 birch cab and use it with my Egnater Tweaker 15 and also as an ext. speaker for the Blues Deluxe. That birch cab sure makes that stock speaker sound really good and I might be making a cab switch for the Blues Deluxe or putting the guts in a head cab.

Thanks for posting this info, mucho good...

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Thu Nov 22, 2012 8:08 am
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Rock Star
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majorbytes wrote:
Quote:
By this time I had learned about the real "tweed" amps from the 50's. Hey, the BDRI looks like a tweed amp. Can it be made to sound like one? Well, no. But I did learn that several tweed amps used a 12AY7 (gain factor of about 40 - 45) in V1. Why not. First I tried a EH 12AY7. I was not impressed. Then I said to myself "The 5751 is an NOS JAN tube. Maybe an NOS JAN 12AY7 would sound better". So, back to Mike K I went for some NOS JAN 12AY7s. Now my amp looked like this:

V1 = 12AY7
V2 = 12AX7
V3 = 12AX7
V4/V5 = 6L6GC


I really like my Blues Deluxe and it is one of my go to amps when I get creative. I think I am going to do the above tube swap, which ones did you get from KCA...
I did the C-Rex speaker about a year ago, big difference. I put the stock speaker in a 1 x 12 birch cab and use it with my Egnater Tweaker 15 and also as an ext. speaker for the Blues Deluxe. That birch cab sure makes that stock speaker sound really good and I might be making a cab switch for the Blues Deluxe or putting the guts in a head cab.

Thanks for posting this info, mucho good...


Here you go:

http://www.kcanostubes.com/content/nos-jan-ge-12ay7

All the other tubes are JJs.

Circuit mods coming. Been a little busy. :D

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Thu Nov 22, 2012 8:25 am
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Aspiring Musician
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Joined: Wed Jul 07, 2010 5:58 pm
Posts: 385
Location: Montana
Thanks...
What about these? V4/V5 = 6L6GC

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Thu Nov 22, 2012 6:38 pm
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majorbytes wrote:
Thanks...
What about these? V4/V5 = 6L6GC


JJs from Eurotubes. Link was posted earlier in this thread.

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Thu Nov 22, 2012 7:11 pm
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Rock Star
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Ok. Since everyone is full of turkey and probably sleepy, we'll start with a super easy circuit mod. But first:

CAUTION!!! Tube amps contain high voltages that can be lethal. Be sure to check the power supply caps with your DVM prior to working on your amp and drain the caps if necessary. Make sure your amp is unplugged and never stick both hands inside a live amp.

Whew. I'll be repeating that several times in this thread.

Ok. The first mod is to the reverb circuit. The BDRI uses a three spring tank with IC drivers and receivers. It's not the best reverb in a Fender amp, but it is pretty good.

The reverb level control uses a treble bleed circuit consisting of a series resistor and capacitor (R103 and C52) as shown here:

Image

This circuit has a tendency to thin out the reverb sound at low levels and higher levels of reverb can sound kind of muddy in comparison. A common and very simple mod is to break the bleed circuit by lifting one end of R103 or removing it completely. I removed it completely. R103 is located right behind the reverb pot as seen here:

Image

The nice thing about the BDRI PCB is that all of the component solder pads are through plated. That means the inside of the mounting holes are copper plated and there is a second, small solder pad on the component side of the PCB. In most of the mods I will talk about, components can be changed without pulling the PCB out. You can heat up the component lead and carefully pull the component out. To replace it, trim and bend the leads to length and place the lead over the hole. Heat the lead and gently push the lead through the hole. That will melt any solder in the hole and on the opposite side of the board. Add a touch of solder on the component side and voila! You're done.

The easiest way to remove R103 is to heat up one of the leads and use a dental pick tool to carefully pry up one end. Then grasp the loose end with a pair of needle nose pliers or tweezers, heat the other lead and pull the resistor out of the board. You have made you first circuit mod.

Breaking the treble bleed circuit will make the reverb a little darker, but more consistant sounding throughout the range of the reverb level control. You might want to just pull one end of the resistor and try the amp out to see if you like the sound. If you do, pull the resistor out all the way. If not, solder the lead back in. Make sure the power supply caps are drained before sticking your soldering iron back in there. :wink:

Tomorrow night: Replacing the power tube screen grid resistors. See you then. :D

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Thu Nov 22, 2012 7:53 pm
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Aspiring Musician
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Joined: Fri Mar 16, 2012 12:49 pm
Posts: 838
bluesky636 wrote:
CAUTION!!! Tube amps contain high voltages that can be lethal. ...
I suspect this falls outside the scope of your thread, Bill, and probably redundant for those who know their way around the inside of a tube amp, but I'm wondering if you would be willing to give a safety lesson along with the step by step explanations. For example, how to safely discharge the evil capacitors.

I for one, and I'm sure many others like myself who would love to tinker, explore, and learn but are :cry: :cry: :cry: :cry: ... would benefit greatly. However, if you find that this will just slow things down, I understand totally. No worries. :)

Cheers!
BM

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Thu Nov 22, 2012 10:01 pm
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Rock Star
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Joined: Mon Apr 05, 2010 2:37 pm
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Location: Natural Bridge, Virginia
Bluer Monkey wrote:
bluesky636 wrote:
CAUTION!!! Tube amps contain high voltages that can be lethal. ...
I suspect this falls outside the scope of your thread, Bill, and probably redundant for those who know their way around the inside of a tube amp, but I'm wondering if you would be willing to give a safety lesson along with the step by step explanations. For example, how to safely discharge the evil capacitors.

I for one, and I'm sure many others like myself who would love to tinker, explore, and learn but are :cry: :cry: :cry: :cry: ... would benefit greatly. However, if you find that this will just slow things down, I understand totally. No worries. :)

Cheers!
BM


This may be overkill, but better than being killed:

http://www.justinholton.com/hotrod/caps.html

I find that the BDRI drains down pretty quickly after power is removed. After a few minutes the caps are all down under 50 VDC. I use this (bought it when I built my 5F6A Bassman kit):

https://taweber.powweb.com/amptechtools/stick.htm

Image

to get the caps down to a couple of volts. Could have built it myself, but at the time it was easier to buy it.

This is good to read:

http://www.aikenamps.com/SafetyTips.html

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Fri Nov 23, 2012 6:43 pm
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Rock Star
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Location: Natural Bridge, Virginia
Ok. Tonight we're going to talk about replacing the power tube screen grid resistors. This was not so much a mod as it was a repair. Details of the troubleshooting methods I followed can be found here:

viewtopic.php?f=13&t=74557

CAUTION!!! Tube amps contain high voltages that can be lethal. Be sure to check the power supply caps with your DVM prior to working on your amp and drain the caps if necessary. Make sure your amp is unplugged and never stick both hands inside a live amp.

This warning is particularly important for this discussion as you are directly exposed to 400+ VDC when replacing the screen grid resistors.

Just to summarize, I was attempting to check the power tube bias on the BDRI when I found there was no cathode current flowing through V5. After several rounds of troubleshooting, I found that the screen grid resistor for V5 was open. Further testing led me to realize that the V5 screen grid itself had shorted. The tube had failed. Since the V5 screen grid resistor failed, I decided to replace both the V4 and V5 resistors. The resistors are shown in the schematic here (I'm not going to get into details about what the resistor is for. An explanation can be found in several of the books I referenced earlier).

Image

The resistors are physically located on the power tube sub-PCB on the underside of the board. You can see them and the component number when looking under the board.

Image

To remove these resistors, you can use the same technique I described to remove the reverb pot treble bleed resistor. To make things easier, I installed the new resistors on the top side of the board (Remember what I said about the PCB being through plated?).

Image

The stock resistors are 470 ohm, 1 watt metal film resistors. I used 2 watt resistors for the new ones.

If you want to turn this into a mod, shimmilou recommends using 2K ohm resistors instead of the stock 470 ohm resistors. This will reduce the voltage to the screen grids a little more than stock and give a little more compression effect to the sound.

The next discussion will be about mods to the bias circuit and an interesting change made by Fender to the bias circuit that has not been documented in an updated schematic. I'll probably post this Sunday as my wife and I are going to see Joe Bonamassa Saturday night at the Warner Theater in Washington, DC. We are pumped for this. :mrgreen:

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Mon Nov 26, 2012 4:44 pm
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Location: Natural Bridge, Virginia
Ok. My hearing has recovered from the Joe Bonamassa concert last Saturday. Fantastic show. 2 1/2 hours of outstanding playing. No opening act. No intermission. Just Joe B and his backing band.

Tonight we're going to talk about modifying the BDRI's bias power supply circuit.

CAUTION!!! Tube amps contain high voltages that can be lethal. Be sure to check the power supply caps with your DVM prior to working on your amp and drain the caps if necessary. Make sure your amp is unplugged and never stick both hands inside a live amp.

I've always had a problem with the bias power supply in my BDRI. I could never bias the power tubes as hot as I wanted to. The B+ voltage drops quite a bit and I could never get the cathode current high enough to set the power tubes any higher than about 57% of the maximum plate dissipation. This mod actually started out as a troubleshooting effort to try and figure out why my B+ drops so much. I documented things in detail with a lot of measurements and test. You can read about it here if you want the gory details:

viewtopic.php?f=13&t=74557

I'm just going to summarize the mods here.

The schematic for the BDRI bias power supply looks like this:

Image

However, as soon as I started to try and trace out the circuit in the amp itself, I found that the schematic in no way resembled what was in my amp. In fact, after some investigation, I discovered that the bias supply in my BDRI was the same as the bias supply in the later Hot Rod Deluxe III:

Image

Note that besides a few component value differences, the HRD III bias supply uses a full wave rectifier vice the half wave rectifier shown in the BDRI schematic. The only thing I can figure is that there was a running change in the BDRI design that has not been documented in an updated schematic from Fender. But I still had a problem with not being able to bias the power tubes like I wanted to.

As I noted in the other thread referenced above, I could find nothing wrong with the power supply caps or any other component that would explain the large drop in the B+ voltage as cathode current increased. Based on all of my measurements, I concluded that the power supply was working as designed. So, how could I increase my bias voltage to where I wanted it?

Looking at the HRD III bias circuit, note that R82 and R77 are used to set the bias voltage. I knew that by decreasing the value of R77, the bias voltage would become more positive which is what I needed in order to bias my tubes hotter. So I decided to decrease R77 from 68K ohms to 56K ohms. R77 is located right next to the bias adjustment pot:

Image

Image

BINGO! Just that slight change was enough to allow me to raise the bias level for the power tubes. I now have the tubes set at about 67% of maximum plate dissipation. At that level, cathode current is 52 mA (average for each of the two tubes), plate current is approximately 50 mA, and plate voltage is about 402 VDC. This works out to be a plate dissipation at idle of 20 watts per tube. I can go hotter if I want, but the plate voltage drops below 400 VDC.

As an aside, since I use a bias probe to measure both the cathode current and plate voltage, I decided to remove the bias test point resistor and diode from the PCB and run the cathodes of the power tubes to ground. I just installed a jumper in the holes where the test point resistor was:

Image

I found that doing so resulted in a slightly more accurate bias reading with the bias probe as well as a little more stable cathode current.

Over the next few nights we will talk about mods to the phase invertor, negative feedback loop, and power output stage to bring the PI and power stage more in line with the 5F6A Bassman configuration. Stay tuned.

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Last edited by bluesky636 on Sun Dec 02, 2012 5:05 pm, edited 2 times in total.

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Tue Nov 27, 2012 6:08 pm
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Rock Star
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Tonight we're going to talk about mods to the phase inverter plate resistors.

CAUTION!!! Tube amps contain high voltages that can be lethal. Be sure to check the power supply caps with your DVM prior to working on your amp and drain the caps if necessary. Make sure your amp is unplugged and never stick both hands inside a live amp.

One of the functions of the phase inverter plate resistors is to set the gains of the positive and negative halves of the phase inverter tube. Ideally it is desired to have the gains of the two halves as close to equal as possible. The BDRI PI plate resister schematic is shown here:

Image

Notice that Fender used the equivalent of 100K ohm resistors on both halves of he PI. The result of this choice is an imbalance in gains for the positive and negative halves as shown by this calculator:

Image

I assume that Fender deliberately created an unbalanced phase inverter output in order to more easily cause distortion in the power tubes. Most other Fender amps have a balanced output from the PI. Since I wanted to model the BDRI PI and power output stage after the the 5F6A Bassman, I decided to change the plate resistors for the inverted output to match the Bassman schematic:

Image

Replacing the 91K ohm and 9.1K ohm plate resistors with one 82K ohm resistor for the inverted output results in a better balanced output from the PI:

Image

The calculator can be found here:

http://ampbooks.com/home/amplifier-calc ... iled-pair/

Note that "RGpa" in the calculator is the grid resistor for the power tubes, not for the PI tube.

It should be noted that HRD III also uses 82K and 100K ohm resistors for the PI plate resistors.

Now, here it the tricky part. R23 and R57 are located underneath the tube PCB behind the PI tube and up against the amp chassis:

Image

In order to access them, the tubes need to be removed and the PCB disconnected from its mounting posts and gently swung forward and down. You have to be very careful doing this because of the ribbon cables that connect between the tube PCB and main PCB. Sorry, but I neglected to take any photos of this. This mod is not for the faint of heart, so if you decide to do it, use caution.

The mod itself, once you gain access to the two resistors is simple. Remove R23 and replace it with a short piece of insulated wire to act as a jumper. Then remove R57 and replace it with an 82K ohm, 1-watt resistor. R58 is not touched.

This mod by itself probably does not impact the sound of the amp that much unless you routinely play the amp loud enough to achieve power tube distortion. The power amp does seem to be a little cleaner sounding with the balanced PI output than with the stock configuration. I'll address the overall changes in sound to the amp at the end of all the mods.

Tomorrow night I'll talk about modifying the negative feedback loop from the power transformer output to the phase inverter input.

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Last edited by bluesky636 on Wed Nov 28, 2012 10:42 pm, edited 2 times in total.

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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Tue Nov 27, 2012 6:50 pm
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Bluesky, I was told that the use of 82K-ohm on one triode and 100K-ohm on the other is a product of imbalance due to long-tailed PI topology. Best summarized in Valve Wizard's site:

" Balance: Because this circuit does not use a constant-current sink in the tail, the two outputs will not be perfectly balanced if both triodes have the same value anode resistors (although balance will be pretty good all the same). The difference in gain between the two outputs is given by:


A1/A2 = 1 + [(Ra+ra)/(Rk(mu+1))]
Where Rk is the total tail resistance Rb+Rt.
In this case we can see from the characteristics graph that ra = 40k, mu=45:
A1/A2 = 1 + [(82k+40k)/(47k(45+1))]
= 1.06

This calculation is for a 12AY7 Long-tailed PI. The difference in a 12AT7 or 12AX7 is greater.

So the inverting output will be 6% higher than the non-inverting output. This could be corrected by making Ra1 6% smaller in value, but in practice it is not necessary; a slightly unbalanced phase inverter is often quite benificial to guitar tone, due to the additional 2nd harmonic it introduces. Nevertheless, this is why the 'traditional' version of the circuit also uses mis-matched anode resistors. "


http://www.valvewizard.co.uk/ACltp2.jpg


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Post subject: Re: Modifications To The Fender Blues Deluxe Reissue Amp
Posted: Tue Nov 27, 2012 8:04 pm
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Interesting stuff. Noting that the HRDlx uses 82K and 100K for the two PI Plate resistors, resulting in a balanced PI output, but the OT primary is imbalanced, approx 82 ohms and 118 ohms. Maybe this OT primary imbalance also adds the second order harmonics, the same as an imbalanced PI output? I have not seen any other similar Fender amps that have an imbalanced OT primary. It is designed this way, I have even purchased a new OT from The Triode Store for comparison. Thoughts?

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