About 5:09 I said "coupling caps" when I meant "filter caps." I do know the difference. Just misspoke in the heat of amp battle.

Damn you know your stuff and I can for sure learn a lot watching your videos which I just started to do. I bought this Western Tolex new from Sweetwater because as we all know Fender made this amp exclusive for sweetwater. But ty for your knowledge im sure to lean a lot from your videos so thank you for sharing....

Tweed blues Jr I bought in 2019 biased at -12.7 vdc from factory. Don't remember the plate voltage but my line voltage is pretty steady at 120.0 AC. Was equipped with GT number four rated el84 JJ's. Seemed to run cool to me and sounded great. Sold it to a friend who wanted it.

Well said . A steady source of income without having to diagnose the well known problems .

In terms of reliability and longevity - what a huge difference between the amps Fender made in the sixties and the ones they make now. It was not uncommon for say, a 1966 Deluxe Reverb, to not require any major servicing (not counting replacement of bad or weak tubes) until 1996 or even beyond. I’d remove the chassis and everything inside would be 100% stock. With the current models you’re lucky to get 3 or 5 years of reliable service, and that’s predicated on diligent babying of the amp so the jacks and pots don’t break. Crazy.

Have (2) Peavey Classic 50s in for retube The NEW crop o tubes ( Globalist specials) are HOTTER than 4th of July I pulled R-18 ( 18K) N put a 10K in Amps sounds much better! I took your fix on the BJ bias circuit , and appreciate it! Was stationed in Memphis Tn 1982-1985 some of best years of my life, still friends w/my friends made bk then! Solomon n Alfreds was there while in school, Paulettes French restaurant, etc...... Been fortunate to build for DiazAMplification, Matamp USA, and Questone.. It all started in Hotlanta traded a perfect JCM-800 for a broke MODDED 100 watt SL Master volume.....It had what i blv was the very primal circuit Peavy would use in the 5150, this was B4 it came out! Love to still have it!

My IV is completely different!!! A black PCB with very different caps and diodes. Also very heavy lifted pwr resistors.

It maybe apples to meatloaf, but this reminded me of Eddie Van Halen having a tough time convincing the Fender engineers of what he wanted for his 5150III amps. Eddie always had his amps at cold bias. There is a certain grind tone with cold bias. And if he knew how messed up we would be today with no tubes coming from Russia, and people running their tubes hot, he would be, “I told ya so!” Only if Fender really gave a damn for us as they were forced to do by EVH.

I just purchased a new Blues Junior Lacquered Tweed LTD. when comparing the circuit board to the one in the video there looks to be some noticeable differences. I’m by no means an electronics wiz but it looks visually different. I wonder what changes were made to mine? I can tell you the reverb is very tame and the tone is not overly trebly.

Mk IV Series 2 is now class A mode! The ones with the dark coloured main circuit board. Mine blew a power tube luckily within the 3 months warranty. Fender warranty tech here in Australia is now fixing the resister issues and installing new tubes under warranty but making further changes at MY expense to make it reliable.

ha ha.. my Laney cub 12r has an adjustable bias voltage ,, right now I am running it at 296V plate and -12.9V bias.voltage . nice and cool,, have not meassured the drop in voltage over the output transformer. ,,

My friend recently bought one of these (tweed version). I think I should have him bring it over and do this mod.

Indeed, one of my final tubes in PJ IV burned out. Tech modified bias, it was too hot…

I believe they want you to buy "Fender brand tubes" and that's why they bias these so hot. They are hoping to make some extra money like when you buy a printer for your computer cheap but they screw you on the cost of ink.

What similar amp do you recommend?

My Blues Junior IV has the black circuit board and is Cathode Biased. (no longer fixed) Have you had one of those on your bench yet? Any thoughts on that move by fender?

Hi, great video! I've been thinking of buying a first fender amp. Thinking aubout a princeton reverb. What's your opinion on princetons with 10 inch vs 12inch speakers(like a Cannabis Rex)? I'm looking for a somewhat authentic surf-rocky/italo-western sound that could be pushed to a tighter overdrive sound at full break-up. Thanks :)

With the newer circuitry of the version IV, and with your addition of the parallel resistor at R51, does this basically convert the BJ IV into an amp that will not need ANY re-biasing in the future?

I played a recent brand new Blues JR. Tweed with Jensen speaker and noticed that you could get a pretty high gain sound at a very low bedroom level which the older ones couldn't do. High gain in the rock and blues sense not metal. I was pleasantly surprised though because. It's hard to find a tube amp that get that gainy of a sound at such a low volume. Did they chain the whole preamp or what? Maybe a better master. Just curious if anyone else noticed that?

Why does this Blues Junior IV have a green Blues Junior III (2017) circuit board? This is the same amp in the video that had the input jack replaced. BJ IVs with black circuit boards (2019 date on pcb) are cathode biased. BJ IIIs with green circuit boards (2017 date on pcb) are fixed bias. This BJ IV is s/n B822461 which appears to be a BJ IV with a green BJ III circuit board.

I think you explained the reason perfectly - Fender is able to sell the same amp over and over again to the same customer. How much of their repeat customer base would go away if they made the simple fixes you and others have pointed out over and over again?

Hey man, you’ve got me second guessing getting a Blues Junior IV. I just need a small practice amp that won’t leave the house. I watched your other videos and now I have no idea what to do because it doesn’t seem like you approve of the Blues Junior or the Supro Delta King 12. Looking at those two and the Vox AC10 or 15, something around that price point. Not worried about the tone, just wondering which one of those you’d recommend or will hold up for more than 3 years. Or which one is the lesser evil? Any advice?

I may have missed it, but did you confirm that the resistor value should be 29K ohms?

What wattage resistor should be used for the 82K resistor added at R51?

UF1007 or other soft recovery fast diode far less noise in switching with low cost . Not getting in to exotic pricey stuff.

Yes, in my blues junior IV : R52 27 kOhm R51 33 kOhm. A 82 kOhm in parallel to R51, it's valid for all blues junior IV ?

There seems to be a fundamental misunderstanding (even on behalf of the manufacturers) of the difference between fixed and cathode bias. It seems everyone just assumes EL84s are to be biased over 100%, regardless of biasing method.

Lyle: was this unit actually labeled “Blues Jr IV” on the rear panel?

I don't understand this common issue of biasing the valves so hot. You don't gain anything except poor reliability. Maybe one day we'll get to meet one of their designers so we can ask.

Hey Fender. Hire him. As a consultant. If he'll have you. Sorry Lyle. Had to say it. While the 1st amendment still applies.

Still sounds beter yhen most amps

How intentional do you think such seemingly obvious mistakes for a famous world’s leading amp manufacturer,are? I mean it wouldn’t surprise me if most owners of blues jr’s probably just wind up buying a new one when the output tubes go. I can’t blame them for that either if they’ve had experience with modern pcb based gear and just assume it’s dead when something goes bad.

hi, so a 2022 blues jr 4 i bought last month now seems to have 27k at BOTH r51 and r52. they also moved the circuity around physically from even previous 4 versions. 2 questions... 1. going from 33 and 27 on the version on this post to 2 27k at both r51 and r52... does that FINALLY fix the problem? the power tubes still seem to run on the hot side. question 2. are r51 and r52 still the bias positions on this new blues jr 4 (lets call it 4.1) version or has even the numbering now changed? I cant seem to sort that out on the schematics. I color coded the two resistors at r51 and r52 on my blues jr 4.1 and they are both 27k. I guess that leads to a 3rd question.... is that a weird thing to have both r51 and r52 (assuming they are still bias) at the same value? the actual resistors are physically larger at those positions (like the 82k you often put in parallel to cool them down), and as I mentioned, they are no longer in same physical location on the board. I saw this comment on the changes they have made on a thread dated july 2022 (www.tdpri.com/threads/fender-blues-junior-iv-schematic.1104154/) what do you think? "- pcb is black with white writing - C4 changed to 2.2uF from 22uF - C8 changed to 0.022uF from 0.0022uF - Fixed bias power supply components R51, R52 & C33 removed from power section - Cathode bias added - C10 - 22 uF, C33 - 22 uF, R51 - 270 ohms, R52 - 270 ohms, R31 & R32 connected to ground - Reverb section input now taken from plate of V1-A before tone controls - Reverb tank is a Ruby Tubes RRVS-3EB2C1B which has same specifications as a 8EB2C1B being 800 ohm input, 2575 ohm output - Resonance circuit added in NFB path - C9 0.047 uF, R60 100K ohms - The power transformer part number for 240v export model is different. - Speaker is a Celestion Type-A 8 ohms. Some BJ IV models have used Jensens." like I said, tubes seem hot to me compared to my vox ac15. love the channel... lots of fun and I have learned so much!!!!

I wonder why Fender keeps the wrong Bias Voltage by keep using the incorrect biasing Ratio? I guess they keep hiring EE engineers that have a below 1.0 grade point average or what

Simple math my friend, fix the problem sale less amps. Long gone are the days of long lasting quality. Like many Fender to don’t care about the costumer only the dollar. Resting on there reputation. Sad but true.

Why would Fender fix it? They want you to buy another amp to replace the one that fails.. they are keeping themselves in business.

It's what I'd call penny wise and pound foolish of Fender to bias the tubes so hot. Guess they want the amps to be disposable but who would buy another after their first one failed. Are these IV series biased differently that the previous versions? There's one thing I've noticed about these amps. They have a lot of gain in the pre-amp stage that makes the volume knob not have a gradual increase to the point if breakup. It seems they get loud really quick from 2 to 3 breaking up a bit too early. At first I thought there was something wrong with the volume pot but that doesn't seem to be it. Have you ever done any mods to fix this? Thanks for your honesty and sharing your knowledge.