Your videos are so helpful. A few months ago my Blues Jr sizzled out while I was playing. I started researching blues Jr repairs, and I found your RU-vid channel. I replaced a screen resistor and the power tubes, and my amp was working again. I have noticed that since the repair was made, the idle buzzing is more noticeable than before. Then I decided to replace all those giant capacitors, but the idle buzz is still very present. Many forums online, people say “it’s a tube amp, they are noisy!”, but I know my blues Jr was never this noisy before. After watching this video, I am certain that I need to replace the valve board in my amp. It just makes a lot of sense, since the power tube burnt out after the screen resistor failed. That burnt out tube must have fried the traces on the valve board.
Hi Riley. Yes it's certaanly possible that creplacing the valve board might help. In any case it's a great precautionary upgrade as you get a bias pot too, and also get rid of that potential track arcing issue..
@@kyledriscollmusic I didn’t replace the board, but I did reduce the noise I was getting by tidying up the wires inside the amp, and also tightening all the nuts on the pots and jacks.
Great video Stuart.. Not only watching you correctly diagnose the issue, but fixing it, plus demonstrating and proving the problem with these poorly designed valve boards. The FBJ are great sounding amps that are very usable .. For the sake of a few quid more on the sale price they could use better quality parts and components.
Thanks Stuart!!! I love your videos!!! I will be doing this mod to a cheap Junior I bought as part of my learning curve. Thanks so much for your very informative videos mate. Look forward to more stuff from you and thanks for all the little trade insights and stories of blokes that taught you along your way. Cheers and Happy Easter from Australia.
Nice to see real experimental evidence at the end. Just goes to show heaters should be wired using a twisted pair of wires and valves should not be mounted upside down on a pcb.
Hey Stuart, Just excellent video..! Great repair and all those tests at the end with the suspect board, who would have thought that the heat from those valves would cause such a problem..So much learned today, thanks for sharing..Top job as usual..Ed..uk..😀
Watching you use that "megga" brought back memories of how we reminded apprentices to make proper tea and not nats wee..... "Oi nipper hold this" or, charge up a cap and "Oi nipper catch".
Interesting analysis with the insulation breakdown testing. Especially the heater tracks, given that good lead dress is to tightly wind the two wires together. I'd really like to see a test of various wires / insulation types (silicone, plastics, fiberglass, etc.) separated and wound together. Heated and unheated, of course.
Brad's Guitar Garage in Oz designed, and sells, his own similar output boards; I don't remember if they're for the FBJ or one of the other Fenders like the Hotrod Deville.....but cist of shipping from Oz might be prohibitive, unless he's having them made in and drop-shipped from another country. You can watch him swap a board out on one of his archived RU-vid streams.
Hi Stuart. If I recall correctly, Lyle of Psionic Audio had a hum problem on a blues junior and to solve it he moved the ribbon cable away from that blue wire that goes roughly to the centre of the main board. Worth a shot.
Hi Martin. Degree in electronics then to the BBC as a studio engineer. Got bored, started my own design company. Made my fortune. Now repair amps for fun and pocket money!
Great job and info! I have the same loud hum problem w/ my Fender Pro jr. I'm sure it has the same poor design as the blues jr. but I love the sound. Is there another fender amp of this size and sound quality that's made better and doesn't have this hum problem you could recommend? Thanks again.
Fascinating Stuart! I particularly enjoyed the use of the heater and the Megger. This helps to understand the issue with greater clarity. Are these design flaws the result of cost or just Schoolboy as you say? Thanks again for an entertaining time.
I seen on other videos with this amp ( I own a type 4 ) pushing the blue wire away from the ribbon cable which helps a lot for a simple fix . No soldering easy fix . But I see your burning on the board is a problem also .
Awesome video, I am learning so much from these, particularly as I recently replaced my Blues Jr. tube board with a similar model from the same manufacturer (the one I purchased, alas, doesn't have a trim pot on). I do have a question about the measurement of bias with your "quick and dirty" method. When I measure the voltage difference between the RED and the BROWN pins, I get a certain amount, say 3.9v (I realize this is a lot, which means I must tame that bias!). However, when I try to measure the diff between the BROWN and BLUE pins, my meter freaks out, beeping as if overloaded, and no discernible amount comes up. The amp also makes a bit of a crackling sound when measuring RED/BLUE. The amp has a healthy clean sound with not much hum with good volume at the moment. Should I be concerned about the above? Many thanks, Alejandro
My Fender bassbreaker 007 produces a low tone hum. It's a single ended design. I've read that all single ended amps have hum. This being a fender amp, makes me wonder if I can reduce the hum.
Hi Stuart I've so chuffed I stumbled on you great videos. So are there an awful lot of problems with the FBJ? Or is it just the fact that there has been so many of them being sold, they show up in workshops more often just due to numbers sold?? Keeps the vids coming. Blessings.👍
Hi Steve. FBJ suffer from a small handful of design problems. This, coupled with the fact that it is a top selling amplifier, means I get a fair few my way. I do like this amp though. You could own one fault free for many years. You could also invest a bit and get the faults fixed before they show themselves.
Yes it's a bit 'quick and dirty' but the output transformer has a DC resistance of about 100 ohms per half winding. So if you measure the voltage across one half widing winding (e.g. RED to BROWN) then by ohm's law you can get the current. So if you measure say 2.5V then that means 25mA bias current.
something like 13years ago, i was buying a new amplifier. Almost went for a Blue Junior, but instead i got an AC15C1 brand new from a reputable shop. 13 years after, i never was so happy to buy an AC15C1 and not a fender amp. All the fenders i was looking for are now plagued with bad capacitors and whacky pcb.
Like you say Stuart, all these Fenders that use these type pcb designs, pro junior, blues junior, deluxe models and Deville models, are great amps once the common faults are remedied. I have a 4 x10 Deville that I bought a good few years ago and the first job was to upgrade all the crap in it. Caps, resistors, diodes, channel switch, new jack sockets and valves. It has been a fantastic amp and still is. Shame on Fender for producing a crap design!! The plus point is 2nd hand prices are low so buy used and upgrade to bag a great amp 👍
Thanks for this video. I have the same problem on a Peavey classic 50 - arcing from trace to trace on power tube pcb. "Engineering" ? What happened to common sense ??
I think Fender should have done a recall on these amplifiers to replace those boards. That's a student level design flaw that happened and it should never have been approved for production until it was fixed. If it was my company, I would have put out a service bulletin on the website and reimbursed the customer's expenses for that repair. Should not have happened in the first place.
How much High Voltage is the MEGGER applying to the circuit board traces? Are you applying the MEGGER to ANY of the tube socket pins or can the MEGGER damage the pcb board?
@@stuartukguitarampguy5830 Can you apply the MEGGER to any traces with components populated on the pcb or this will damage the components populated on the pcb? The tubes heater 6vac/6vdc traces will be like a short circuit/closed loop so this is like shorting out the MEGGERs probes together which I would think would damage and short out the MEGGER because you can't both MEGGERS probe leads together while pressing the MEGGERS test button or it will damage the MEGGER?
@@waynegram8907 The Megger is high voltage but very low current. Think if it as 500V DV in series with say a 1 Meg resistor. You can short the probes no problem. If there are any semiconductors (transistors or chips ) in your amp then the Megger will fry them in an instant. If you have an all valve amp, then you can use the Megger okay but I'm bothered by your question because you don;t use a MEgger by just randomly sticking the probes where you feel like it. Most places willl have some DC resistance so the Megger will always show that. It's for measuring insulation resistance, i.e. those places where there should be an infinite resistance. So you could remove a suspect high voltage capacitor, put it on the Megger and see if there is any leakage. Or you could do what I did in the video and check the board insulation betwen tracks on a depopulated board. I hope that's clearer.
Thanks . I now know for sure (just by looking) at the utter "Cheapness" that Fender is using in it's products. As a retired Electronics Engineer, I know that that is the crappyies board material available. I wonder how many "ounce copper" IS USED. ( The least grade brd. Material I used was FR-4)
Hi stuart i watched one of ypir videos about replscing a pot on the blues junior treble control ,i have the same on my reverb control tap it its on then it goes off !! Ive tried to find a replacement but to no avail .would you happen to have a source for these not sure what value it is think it maybev 50k but not 100% any ideas Stuart .
Hi Andrew If it's had a knock on the shaft it MAY be pissible just to tighten the bent pieces of metal which hold the pot together using a pair of pliers. Otherwise you'll need to replace the pot. It is a 50K type 'B' taper (e,g, B50k) and I believe they are called 'snap in' pots.
@@stuartukguitarampguy5830 Hi stuart these amps though great can be a pain !! Will have a look ,but at the worse outcome a replacement is needed i suppose i could hand wire a traditional pot and bypass faulty one maybe!! Or im competant enough to solder a new one in . if this is the case have you any in your stock more than willing to pay extra for whatever you want Stuart !! .
I noticed the replacement board has some resistors pre-installed on it (presumably screen resistors). Did you have to remove any resistors from the main board, other than changing the bias resistor to a different value?
@@stuartukguitarampguy5830 OK, I was curious about that as I did not see any resistors on the original valve socket board Good repair overall. It's great that someone went thru the trouble of manufacturing upgraded boards for that amp. By the way Weber is pronounced Web-Er as in a spider's web.
@@MichaelSmith-rn1qw Actually that's a very good point and I hadn;t noticed that. I think the new resistors are probably to do with the new bias arrangement. Thanks for the pronunciation. Bet I don;t remember though! The other one I can never recall is Hartke.
@@stuartukguitarampguy5830 Actually, I think Weber is German name, and the way you pronounce it is correct in German. I found a website with audio that gives the pronunciation of words in various languages.
Hello Stuart I noticed after the repair the amp still had a hum. I watched this because my amp a red knob super 60 also now has an almost identical hum and the sound breaks up under high volume. Would you know where to find this fault to help me out.. thanks
Ok, well I've replaced all the large farad caps in the filter stage etc.. I've also done a tap test with an analoge multi-tester, and with the volume on full only the tester shows interference near the output cap stage. And I don't seem to see any cracked solder joins on the preamp valves Do you think a cap or resistor could be failing near the power tubes that cause a breakup and diminish the sound? Hello from S Africa
I checked the ground lines and then powered it on then heard the hum was even louder.. I looked and saw the power valves now red plating! Could this be a cap that has failed Stewart, and I don't have a cap tester device?
It's interesting that the board conducts when it gets hot because most materials in nature conduct best the cooler or colder they are ( that's how superconductors function: lowered resistance at extremely cold temperatures).
There are a couple of thoughts that could be the culprit. Natural conductors usually conduct better when cooler since they are more dense and electrons can move between the atoms more easily (very over-simplified!) But since materials expand when they get hotter, it could be that there becomes closer proximity and minute arcing is occurring. Another guess might be that, there might be a kind of cathode effect happening such as in vacuum tubes. Maybe the hotter conductor, being laden with such high voltages is simply emitting stray electrons just enough to interfere with the too-close other conductor(s). We know that wires conducting, when too close to other audio path conductors can stray electromagnetically introducing hum or other unwanted interference. Just throwing out thoughts of things that could be considered toward the question. Have fun!
@@aceraspire7456 Interesting thoughts thanks. The boards are fibregalass so I'm unsure what conductive mechaanism there could be in that. Marshall definitely had a major problem with this on all their JCM2000 amps.
@@stuartukguitarampguy5830 Sorry I wasn't more clear. I was referring to the conductive traces on the board that seem a bit too close together expanding due to high heat. At any rate, just 'spit-balling' ideas. 🙂
@@aceraspire7456 , interesting hypotheses! Most people don't know this by the way, but ordinary printed circuit boards and phenolic terminal strrips are often carbon-based, where some kind of cellulose or wood pulp material is impregnated with epoxy resins. The best? PC boards are made out of fiberglass, and so the fibers are glass or silica and only the resins are carbon based. ( Tube sockets are also often made of a phonalic material which is why they can sometimes arc and become conductive). PS, Some might argue that Teflon is a better insulator and a more appropriate material to use for circuit boards. Certainly it would be he resistant, but I don't know what's involved in getting copper foil plated onto and bonding securely to Teflon. Also, I used to work with a well known engineer at an audiophie amplifier manufacturing company, and he claimed he tried building some of his products on Teflon PC boards and they sounded terrible.
Many electronics manufacturers outsource the builds to places like china. We know that. No new news there. But, what many people don't know is that very often, it isn't just the assembly and construction. Many times, the choice of materials, components, even layout of the circuits are also left to the chinese factories. They are given schematics and basic specs and the chinese company is left to take it from there and send back a finished product at slave-labor prices. As is very well known, china is not exactly a country known for caring a great deal for quality, consideration, safety, pride in workmanship, etc.. Very often, so long as the thing looks nice and doesn't explode before it's sold, the hiring company's lawyers and accountants are fine. Money saved - liability possibility low, reasonably high probability of replacement in a short period of time - forget the customer; our job is to keep the stockholders happy (namely; us!) 🙂 The days of experienced, skilled, honorable engineers being the ones doing the final designs has long since gone by. Even many of the 'mass-boutique' companies are showing serious flaws in design, layout or quality of materials. Just sayin'. Always nice to see skilled people doing skillful work. Appreciate your video
@@stuartukguitarampguy5830 Latency between stroke on strings and sound i get from my amp , it vary from amp to amp and my current amp have lot more latency than others
@@semihkucukay4098 If you have an old valve amp with a tube rectifier and smallish HT caps then when you hit a loud chord, the HT sags (as it cannot cope) but quickly (say 1/4 second?) returns to full value. Guitarists LOVE this feature and it's why they go for these old amps. It's called 'sag'. If you increase the value of the HT caps you will 'stiffen' the HT and this sag will not be as pronounced. Hope that helps.
Well done, Sir, as always. I noted that R51 has two resistors in parallel. Looks like a repair or alteration. That wasn't anything you did, I assume. I'm a self-taught PCB designer for my effect pedals, and even I know you don't put large voltage differences in tightly adjacent tracks! Amateurish design, indeed. And to think they paid good money to someone to design that.
Hi Andy. That extra resistor is the only way to adjust the bias prior to adding the bias pot. So someone before me has changed the valves and rebiased.
I know nothing about electronics and amps. Some people on videos dont touch the valves with bare hands because they say you shouldent get grease from your hands on them. Does this matter? Ive noticed you always remove the valves with bare fingers.
Hi Dave. No it's fine to handle them with bare hands. I think people are confusing valves witth those ultra delicate and VERY high temperature video projector lamps. All the best.
@@stuartukguitarampguy5830 You took great care to flip the new board upside down, insert the ribbon cable ends from the top while upside down, then flip the board back to reproduce the factory route. Wouldn't it have been easer just to run them directly to the top? You said the ribbon cable ends "have to tuck under". The connections would be the same as the new board looks like it is a through-hole and the electrical connection would be the same whether you came from above or below; we're flipping up and down, not left to right. Maybe I'm missing something?
I can;t honestly recall but I'm sure my preferred option would be to follow what the manufacturers originally did. No difference electrically of course. @@toddcallison8087
Great work Young Stuart!! Sorry, I'm old school and love my old Fenders/Musicmans, but I think these (cheap Chinese) circus boards from ALL these Blues Juniors etc etc etc are really rubbish and badly designed, and Fender are NOT doing themselves any favours and ruining their reputation for quality building these cheap crap amps with these cheap componants! (Sorry old fart rant over!!)
@@muntor7935 Did I say that? Can;t recall. Probably a throw-away. I mean 'cheaply mass produced'. Marshall had the same issue with their JCM2000 series. Conductive pcbs.
Kind of surprising that this issue hasn't been fixed or improved over the long history of the amp, and those boards are SO cheaply made. Single-sided boards in the 21st century?
Hi Don. I'd be interested to see the very latest FBJ IV I think. They may hev sorted some of the problems but because this is a newer amp I don't get them in the workshop.
