I just love all the babbling and singing from your toddler! :) Yes a bit invasive but that's a sign of good health and you seem to be a patient dad. I'm glad you left all this funny noise in the VDO, and also, the demonstration was brilliant!
Upon listening to the very informative video, thank you for the information. My stock BJ may need the mods that can be more like a plexi. Can you list the parts that you have mentioned. Thank you.
Great video for anyone thinking about modding a Fender Blues Jr.Although circuit overview should have been done with the schematic for Blues Jr II & III.The position of Volume pot and the tone stack resembles the Fender Bassman so nothing new there.I wouldn't use a 1k pot for bass instead I would use a 1 meg pot just like the Bassman. I can tell you from experience that the best mod for the Blues junior is a 6V6 conversion along with other mods mentioned in this video plus some other mods. The amp sounds fuller and drives the speaker better with 6V6 output tubes. It got a mojo that it didn't have before the mods. Nevertheless I still felt that I needed better cleans and wattage after the mods for gigs especially since I was not miking my amp. Once i got the Fender Deluxe Reverb 68 I sold my modded Blues Jr and I never looked back.I also got a Fender Silverface Champ which sounds better than the stock Blues Jr .If I have to do it all over again I would probably buy a Silverface Champ for home practice or a 65 Fender Pricenton Reverb if I needed more volume. If I wanted to buy another Blues Junior for modding I would find a used one for $250.
This was very helpful, thank you very much! About replacing the Master volume pot - Which pot did you choose? I'm relatively new to modding amps, but feel pretty comfortable replacing components. That's probably the first thing I would modify in the Blues Jr.
The reason the schematics for Blues Juniors as well as many other amp's show the V1B before V1A is because it makes for shorter, more direct wiring from the input to the grid of V1B. Then the wiring from V1B into V1A also continues logically in a more direct downstream direction. You will also see the same thing with V2B before V2A, etc... I suppose if the nomenclature on the schematic bothered you that much, you could rotate all your preamp tubes 180 degrees in the chassis but this could compromise better wiring practices for the heater filaments, cathode and anode.
As far as I know the 1M volume control after first triode is a LINEAR control. The 130K from the wiper to ground re-shapes the control curve of this pot. Fender have chosen to do this to produce a custom volume control curve rather than use a standard curve log pot.
I enjoyed this! And not being snarky here - but thanks for not acknowledging your child making noise every 5 seconds. It’s what kids do and it’s not that big of a deal.
Hi mate that was very informative, I’m from mechanic background and have been added some Billm mods to my blues junior, if this was a hydraulic machine I’d be fine. I have dabbled with electronics over the year so I have a very basic understanding, having you walk through the circuit was great, I was able to follow quite well. I would have loved to hear your explanation of the reverb circuit, mine is not working and it’s driving me mad trying to work it out..
I know this is long in coming, but think of electronics as plumbing. It follows a path to ground, usually after doing work of some kind. Or you get smoke.
Thanks! Best explaination I've seen so far of what all the niddly bits do. My next build will be an Ampeg SB-12, and quite a bit of what you presented will be applicable to that schematic as well. It'll just take me awhile to sort it out...
Thanks for making this Video. Very informative. Great blues Jr Schematic breakdown. I knew it sounded thin because of the low value input cap, fender also these low values also used these small values on its solid state amps and they sound thin. Its not on my to do mods list along with upgrading the tone stack to a more fender classic style. Thanks again!
I had an Epi valve Jr, V1. Bill M was so helpful and wanted to help me out but I'd already sent it out to be worked on by some doosh in Texas. So BillM, helped me without any money, wanted to just help me out. That's rare, buy his stuff kids
I certainly can be wrong and I appreciate the input. Where is the DC coming from? C1 decouples and blocks DC from the V1B plate. The only other source would be the V1A grid, which usually doesn't have any DC on it, right?
I would have to agree with Kley. There are plenty of circuits without the relatively low 130K resistor to ground. The resistor in this position sets bias for the grid and establishes a quiescent anode to cathode current in the tube , and so defines how much excursion above and below that quiescent point the input signal may traverse. Certainly the current coming from the grid is relatively infinitesimal, and all the circuits that have direct connections between the sweeper arm of a potentiometer, and the grid do not overwhelm the pot with any noticeable DC. One gets into trouble (with potentiometers) when there is no coupling cap between a common cathode plate circuit, and the next common cathode grid.
Nope, sorry but you are wrong. R5 is not necessary, in fact, it's in the way. What the next input stage needs is a 10K grid stopper wired close to the pin, that will kill any noise issues and improve the volume control function. C2 is also unnecessary. This amp was poorly thought out, it blocks lows and then tries to either pass or suppress highs. Way to many complications for no attributable reasons.
A quick question. I want to half the output for smaller venues. Would it be as simple as disconnecting pin 2 on one of the EL 84s and grounding to earth so it's not floating? And leaving, depending on which valve is used, R20 or R23 floating. I'd probably put SPDT switch to bring it back to full power. Love the video especially your children in the background
I like the idea of making an biasing pot 18:30. I wanted to do that to my Magnatone M10 which also runs EL84. Enjoyed your vid. Thanks for sharing. c];-)
Yes there have been quite a few mods on YT showing similar schemes for making adjustable bias on the Blues Junior. Yes they seem to be universally set too hot coming from the factory and burn through EL84's quite quickly.
@@Geopholus yes I changed a silver face to a twin reverb adjustable with the help of Gerald Weber. BTW About 3 years ago I was going over the Schematic of the M10 and seen that the tubes used were 7189 s I think they handle the plate voltage better. For some reason I did not question the use of EL84 s Thanks Geopholus for the come back c];-)
The Darby Hewitt paper claims to have installed a 250uf at C4. Has anyone else done this and can you please advise what you installed? I can’t find anything with this value that will physically fit there.
Awesome breakdown of the circuit. What are your thoughts about changing the bridge rectifier from solid state to tube to introduce the sag in voltage that tube rectifiers are known for?
You certainly could. Though you may want to also change the B+ step down resistors and caps. 47uf is pushing it a bit for a tube rectifier as the first filter cap. 2.2k as the first dropping resistor is a bit low. A choke might be a good option there instead. Second, you'd drop some B+, which would change the tone and feel of the amp overall. Perhaps changing the dropping resistors to 4.7k from 10k would offset for that change. A final option would be a sag resistor. Something like a 750 ohm 10 watt resistor between the output of the rectifier and the first filter stage would provide some of that sag feeling. More info here: robrobinette.com/5e3_Modifications.htm#Simulate_Tube_Rectifier
Kley , yes but You need a floating 5 Volt winding for a rectifier tube. A sag resistor would produce a very similar effect, and be easier to implement, and or reverse,... great suggestion there.
Nice walk-through, but went straight over my head due my utter lack of knowledge in electronics. I'm assuming this demonstration pertains to the later creme board generation/s. I have a 1997 green board BJ I'm trying to troubleshoot, which according to my preliminary research and comparison of respective schematics, is somewhat different from the creme board version. Too bad I live in a backwards, underdeveloped part of the world where I have no access to qualified amp techs to take the amp to, which means if I don't figure out how to fix the issue myself, a perfectly good amp is gonna end-up in a junk pile.
Can you also do the same analysis on the Blues Jr III. Seems there are changes to the circuit and I don't want to make changes that would damage the BJ III circuitry.
Thank you for providing us the best BJ modding tutorial with deep explanations. My question is about improving/increasing the reverb effect in an early green board BJ (Rev.B) The reverb effect is injected into to the sound path in an odd way. If you decrease the input volume while turning the master volume up that's fine, you can get the reverb more than needed. However, if you want to get gain and grid by turning the volume up, then the reverb gets subtle and subtle as you increase the input volume which makes the reverb useless. I was wondering do you have a suggetion to fix it? I heard that this problem was fixed in BJ when fender switched to the cream board so that the owners of BJ II and III should not have been frustrated with the reverb issue.
At 12 minutes into your video you mention putting the ground at [R29] from the mid pot on a switch. Can that still be done if the cathode follower mod has already been done to the amp?
Yes as long as the cathode sees ground through the 100K resistor, and if it is a 5F6 config I guess the feedback loop from the speaker needs to be lifted also.
Hi Klay! A week ago my amp worked normal, but now the "FAT switch" has stopped working. It is as if it was always on. Looking for information, I understood how it works, but I still can't find the fault. Could it be that Q1 is failing? Thank you!
I would think folks who play the blues would not want to have a large bass response cause you the step-on frequencies used. by the bass and drums It's kind of true for other types of music as well Most folks I know who want to cut through and be heard lower the bass! So perhaps the designers had it right and what folks are looking for is a marshall or some other amp with the more bottom end?
Maybe, but then the Blues Deluxe has LOADS more bass! I have modded my Blues Junior to have some more bass, but still way less than the Blues Deluxe or Hot Rod Deluxe. They are reducing the bass to some degree to match the effective frequency response of the cabinet size, but have gone a little further. Stops the wasting of the 15w on frequencies that won't project anyway.
if you were to disconnect the Mid pot, the next stage would have no grid leak. The ground of the pot is the grid leak.Am I wrong? Couldn't that mess up the bias of the next stage?
Yes You would need a 1 meg to ground on the grid. You could add that without much change to the circuit, and then lift the mid. I'm not sure why I would want that extra stage even there, if I didn't want tone controls.
1k definitely wouldn't work for the bass pot. You would have no adjustment. 100K would work, but i think he meant one Meg, as it is in several Fenders, and early Marshalls. I like to make the bass cap .047 or more to lower the frequency of the bass pass .
"Infamous" is for things or people who do horrible things that make them famous in the worst possible way. You don't want to be infamous. Charles Manson was infamous, so was Jim Jones, and Lizzie Borden. The word you are looking for is "legendary".
I just love all the babbling and singing from your toddler! :) Yes a bit invasive but that's a sign of good health and you seem to be a patient dad. I'm glad you left all this funny noise in the VDO, and also, the demonstration was brilliant!
Excellent review, thank you. Studying electronics for 2 years and this really helps. Love my Blues Junior III. I did some great mods.
Upon listening to the very informative video, thank you for the information. My stock BJ may need the mods that can be more like a plexi. Can you list the parts that you have mentioned. Thank you.
Great video for anyone thinking about modding a Fender Blues Jr.Although circuit overview should have been done with the schematic for Blues Jr II & III.The position of Volume pot and the tone stack resembles the Fender Bassman so nothing new there.I wouldn't use a 1k pot for bass instead I would use a 1 meg pot just like the Bassman.
I can tell you from experience that the best mod for the Blues junior is a 6V6 conversion
along with other mods mentioned in this video plus some other mods.
The amp sounds fuller and drives the speaker better with 6V6 output tubes. It got a mojo that it didn't have before the mods. Nevertheless I still felt that I needed better cleans and wattage after the mods for gigs especially since I was not miking my amp.
Once i got the Fender Deluxe Reverb 68 I sold my modded Blues Jr and I never looked back.I also got a Fender Silverface Champ which sounds better than the stock Blues Jr .If I have to do it all over again I would probably buy a Silverface Champ for home practice or a 65 Fender Pricenton Reverb if I needed more volume. If I wanted to buy another Blues Junior for modding I would find a used one for $250.
20:30 Joy to the World? Christmas was a month ago!
This was very helpful, thank you very much! About replacing the Master volume pot - Which pot did you choose? I'm relatively new to modding amps, but feel pretty comfortable replacing components. That's probably the first thing I would modify in the Blues Jr.
The reason the schematics for Blues Juniors as well as many other amp's show the V1B before V1A is because it makes for shorter, more direct wiring from the input to the grid of V1B. Then the wiring from V1B into V1A also continues logically in a more direct downstream direction. You will also see the same thing with V2B before V2A, etc... I suppose if the nomenclature on the schematic bothered you that much, you could rotate all your preamp tubes 180 degrees in the chassis but this could compromise better wiring practices for the heater filaments, cathode and anode.
I would love to see your evaluation/thought process on the newer Hot Rod Blues Jr. IV w/the black pc board circuit & schematics.
As far as I know the 1M volume control after first triode is a LINEAR control. The 130K from the wiper to ground re-shapes the control curve of this pot. Fender have chosen to do this to produce a custom volume control curve rather than use a standard curve log pot.
It's listed as an Audio pot.
I enjoyed this! And not being snarky here - but thanks for not acknowledging your child making noise every 5 seconds. It’s what kids do and it’s not that big of a deal.
Amen
Beat on the brat
beat on the brat
beat on the brat with a baseball bat
oh yeah
- The Ramones😁
Hi mate that was very informative, I’m from mechanic background and have been added some Billm mods to my blues junior, if this was a hydraulic machine I’d be fine. I have dabbled with electronics over the year so I have a very basic understanding, having you walk through the circuit was great, I was able to follow quite well. I would have loved to hear your explanation of the reverb circuit, mine is not working and it’s driving me mad trying to work it out..
I know this is long in coming, but think of electronics as plumbing. It follows a path to ground, usually after doing work of some kind. Or you get smoke.
Great circuit analysis. Do you the same for Hot Rod Deluxe !!
Thanks! Best explaination I've seen so far of what all the niddly bits do. My next build will be an Ampeg SB-12, and quite a bit of what you presented will be applicable to that schematic as well. It'll just take me awhile to sort it out...
Thanks for making this Video. Very informative. Great blues Jr Schematic breakdown. I knew it sounded thin because of the low value input cap, fender also these low values also used these small values on its solid state amps and they sound thin. Its not on my to do mods list along with upgrading the tone stack to a more fender classic style. Thanks again!
You are welcome, glad it was helpful!
Great walkthrough! I do really appreciate it!
Hello Kley De Jong, I suppose the fat switch could be used to lift the tone stack? Also, is this the first version of BJ after US production?
I had an Epi valve Jr, V1. Bill M was so helpful and wanted to help me out but I'd already sent it out to be worked on by some doosh in Texas. So BillM, helped me without any money, wanted to just help me out. That's rare, buy his stuff kids
R5 130K is a grid leak resistor for V1A. If you clip it out, the Volume pot will have a DC current thru it and will become noisy.
I certainly can be wrong and I appreciate the input. Where is the DC coming from? C1 decouples and blocks DC from the V1B plate. The only other source would be the V1A grid, which usually doesn't have any DC on it, right?
@@KleyDeJong actually grid do have DC, it is its leak current.
I would have to agree with Kley. There are plenty of circuits without the relatively low 130K resistor to ground. The resistor in this position sets bias for the grid and establishes a quiescent anode to cathode current in the tube , and so defines how much excursion above and below that quiescent point the input signal may traverse. Certainly the current coming from the grid is relatively infinitesimal, and all the circuits that have direct connections between the sweeper arm of a potentiometer, and the grid do not overwhelm the pot with any noticeable DC. One gets into trouble (with potentiometers) when there is no coupling cap between a common cathode plate circuit, and the next common cathode grid.
Nope, sorry but you are wrong. R5 is not necessary, in fact, it's in the way. What the next input stage needs is a 10K grid stopper wired close to the pin, that will kill any noise issues and improve the volume control function. C2 is also unnecessary. This amp was poorly thought out, it blocks lows and then tries to either pass or suppress highs. Way to many complications for no attributable reasons.
A quick question. I want to half the output for smaller venues. Would it be as simple as disconnecting pin 2 on one of the EL 84s and grounding to earth so it's not floating? And leaving, depending on which valve is used, R20 or R23 floating. I'd probably put SPDT switch to bring it back to full power. Love the video especially your children in the background
Awesome, please do the same with pro Jr, maybe with indications like Master + Volume, Presence, FAT.
Love the baby crying !!!!!!
Oh, I thought it was a wah pedal.
I like the idea of making an biasing pot 18:30. I wanted to do that to my Magnatone M10 which also runs EL84. Enjoyed your vid. Thanks for sharing. c];-)
Yes there have been quite a few mods on YT showing similar schemes for making adjustable bias on the Blues Junior. Yes they seem to be universally set too hot coming from the factory and burn through EL84's quite quickly.
@@Geopholus yes I changed a silver face to a twin reverb adjustable with the help of Gerald Weber. BTW About 3 years ago I was going over the Schematic of the M10 and seen that the tubes used were 7189 s I think they handle the plate voltage better. For some reason I did not question the use of EL84 s Thanks Geopholus for the come back c];-)
Need to make a larger curser and or different color . Informative though . Thanks
The Darby Hewitt paper claims to have installed a 250uf at C4. Has anyone else done this and can you please advise what you installed? I can’t find anything with this value that will physically fit there.
Which Blues Junior are showing???
I read somewhere you should substitute C4 using a 250uf electrolytic... or do you think the suggested .047 is better?
Brother this was awesome!! Thank you
Awesome breakdown of the circuit.
What are your thoughts about changing the bridge rectifier from solid state to tube to introduce the sag in voltage that tube rectifiers are known for?
You certainly could. Though you may want to also change the B+ step down resistors and caps. 47uf is pushing it a bit for a tube rectifier as the first filter cap. 2.2k as the first dropping resistor is a bit low. A choke might be a good option there instead.
Second, you'd drop some B+, which would change the tone and feel of the amp overall. Perhaps changing the dropping resistors to 4.7k from 10k would offset for that change.
A final option would be a sag resistor. Something like a 750 ohm 10 watt resistor between the output of the rectifier and the first filter stage would provide some of that sag feeling. More info here:
robrobinette.com/5e3_Modifications.htm#Simulate_Tube_Rectifier
Kley , yes but You need a floating 5 Volt winding for a rectifier tube. A sag resistor would produce a very similar effect, and be easier to implement, and or reverse,... great suggestion there.
Nice walk-through, but went straight over my head due my utter lack of knowledge in electronics. I'm assuming this demonstration pertains to the later creme board generation/s. I have a 1997 green board BJ I'm trying to troubleshoot, which according to my preliminary research and comparison of respective schematics, is somewhat different from the creme board version. Too bad I live in a backwards, underdeveloped part of the world where I have no access to qualified amp techs to take the amp to, which means if I don't figure out how to fix the issue myself, a perfectly good amp is gonna end-up in a junk pile.
Can you also do the same analysis on the Blues Jr III. Seems there are changes to the circuit and I don't want to make changes that would damage the BJ III circuitry.
Thank you for providing us the best BJ modding tutorial with deep explanations. My question is about improving/increasing the reverb effect in an early green board BJ (Rev.B) The reverb effect is injected into to the sound path in an odd way. If you decrease the input volume while turning the master volume up that's fine, you can get the reverb more than needed. However, if you want to get gain and grid by turning the volume up, then the reverb gets subtle and subtle as you increase the input volume which makes the reverb useless. I was wondering do you have a suggetion to fix it? I heard that this problem was fixed in BJ when fender switched to the cream board so that the owners of BJ II and III should not have been frustrated with the reverb issue.
At 12 minutes into your video you mention putting the ground at [R29] from the mid pot on a switch. Can that still be done if the cathode follower mod has already been done to the amp?
Yes as long as the cathode sees ground through the 100K resistor, and if it is a 5F6 config I guess the feedback loop from the speaker needs to be lifted also.
Are you still modding blues juniors? I just got one and am looking for someone to improve the overall quality.
O just one more thing I know it could be a matter of reliability versus sound but what output tubes do you prefer to use on these amps? Thanks c];-)
Question...On a new Blues Jr. 111 can you just clip the wire on C2 to tame the Treble? Thanks!
Yes, x2 is the bright cap and may be clipped out.
@@KleyDeJong Thanks Kley, do I just clip the wire in the middle of C2 and leave it in there?
ur a genius u know what ur talking about the diagram
Hi Klay! A week ago my amp worked normal, but now the "FAT switch" has stopped working. It is as if it was always on.
Looking for information, I understood how it works, but I still can't find the fault. Could it be that Q1 is failing?
Thank you!
That is very likely the problem.
Can you do that for the Hot Rod Deluxe 3?
I would think folks who play the blues would not want to have a large bass response cause you the step-on frequencies used. by the bass and drums It's kind of true for other types of music as well Most folks I know who want to cut through and be heard lower the bass! So perhaps the designers had it right and what folks are looking for is a marshall or some other amp with the more bottom end?
Maybe, but then the Blues Deluxe has LOADS more bass! I have modded my Blues Junior to have some more bass, but still way less than the Blues Deluxe or Hot Rod Deluxe. They are reducing the bass to some degree to match the effective frequency response of the cabinet size, but have gone a little further. Stops the wasting of the 15w on frequencies that won't project anyway.
This is very interesting to me. Thank you for this. Is this the model 3 or model 4 version?
if you were to disconnect the Mid pot, the next stage would have no grid leak. The ground of the pot is the grid leak.Am I wrong? Couldn't that mess up the bias of the next stage?
Yes You would need a 1 meg to ground on the grid. You could add that without much change to the circuit, and then lift the mid. I'm not sure why I would want that extra stage even there, if I didn't want tone controls.
would you please be so kind as to send me a copy of the blues junior schematic, can´t find it anywhere, thnk you so much
Did you try the link that appears in the video?
www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Blues-Junior-Schematic.pdf
The numbers on the components do not match with blonde board...
You said change the bass pot to 1k do you literally mean 1k or did you mean 100k
1k definitely wouldn't work for the bass pot. You would have no adjustment. 100K would work, but i think he meant one Meg, as it is in several Fenders, and early Marshalls. I like to make the bass cap .047 or more to lower the frequency of the bass pass .
Bic Lighter
"Infamous" is for things or people who do horrible things that make them famous in the worst possible way. You don't want to be infamous. Charles Manson was infamous, so was Jim Jones, and Lizzie Borden. The word you are looking for is "legendary".
to much gain? wth is that? is that even a thing?