Thank you Martyn.. I fitted the Keld bias mod to my BJ a few years ago and I'm pleased to report that I did it as you show here. For the price, this mod is 'priceless'. Anyone gigging these excellent amps should take the plunge and fit this mod ( or get it fitted) as the cost of a decent set of EL-84's are getting silly.
Hello Pete, thank you. I agree, it's a fantastic little mod and as you say, the price of tubes these days, it makes sense to fit this mod. Take care Pete.
Brilliant allways wanted to see biasing shunt method on video And i can follow that easily as i get lost with maths n stuff Will check bias a lot easier in future on valve p/p amps With u/l amps i guess its different as there are five connections.. Cheers Martyn... wot no test toon!
I prefer using 10-turn or even 20-turn pots for adding adjustable bias to amplifiers when feasible; knock-off copies of the original tiny blue Bourne trim pots are easily available online nowadays (the ones we used in the audio-repair shop were branded BaoFeng). Anyway, I feel I should echo Martin's concern that adding this adjustable bias circuit from the top, without complete removal of the main board, is NOT a job for newbies to soldering or tube amp repair. The copper foils (that the resistors being clipped out are soldered to) are extremely thin and fragile and are easily delaminated from the board, or the factory solder joints compromised by using too much heat or dwelling too long with the hot soldering iron. If your wire cutters aren't extremely sharp, the blades thin and precise, and if you aren't gentle when straightening the bent stubs of wire, you might break the foils or the solder connection at the underside of the board where you can't see it; and if a connection fails while the amp is being played through, you can measure the life of your tubes and perhaps even the power or output transformer *in mere minutes*. Most people might be better off having a technician add this when they're doing routine service on these amps such as replacing the crappy, known to fail, IC branded electrolytic power supply capacitors.......
Hello. This one didn't have the IC caps in it. From 2019 onward, Fender have changed the bias to Cathode Bias. I think that is a move in the right direction for these amps. Take care.
Hello. That's a really good question. I have just done a bit of searching online, and came up with this: www.indystringtheory.com/service/what-version-blues-junior-do-i-have/I have looked at the pictures close up. The black board is indeed different. That board was introduced in 2019. The Blues Junior in this video is a 2018. The customer checked the bias and it was at 85%. The earlier ones were set at 100%. I have yet to see a 2019 onward BJ. 70% is the best setting for the bias. I don't think the mod will fit on a 2019 board. The mod replaces R51 and R52. I can't see either on the black board, though it is a bit blurry when you enlarge the pictures. You could check the bias using the video? P1, P2, P3 look the same on the black board. Thank you for bringing that one up. Take care.
Hello. I have done a bit more checking. Your amp is Cathode Biased, not fixed biased. So you don't need the mod. I new they had changed over, but I thought it was in the last couple of years. Check the link below. I got there in the end. Take care. www.tdpri.com/threads/fender-blues-junior-iv-schematic.1104154/
Does the BJ have a 240v tap as well as the 230v it comes with from the factory? Putting that right would help with tube life. I did the swap on my PRRi.
Hello. Sorry this comment slipped by me. Just found it while checking some of the videos. Yes It does have a 240 Volt tap. I changed this one over. I am going to be releasing another Blues Junior video in a few days. I go through the voltage change on that one. Thanks for watching and take care.
Thank you Martyn.. I fitted the Keld bias mod to my BJ a few years ago and I'm pleased to report that I did it as you show here. For the price, this mod is 'priceless'. Anyone gigging these excellent amps should take the plunge and fit this mod ( or get it fitted) as the cost of a decent set of EL-84's are getting silly.
Hello Pete, thank you. I agree, it's a fantastic little mod and as you say, the price of tubes these days, it makes sense to fit this mod. Take care Pete.
Brilliant allways wanted to see biasing shunt method on video
And i can follow that easily as i get lost with maths n stuff
Will check bias a lot easier in future on valve p/p amps
With u/l amps i guess its different as there are five connections..
Cheers Martyn... wot no test toon!
Hello Paul, thank you. I am pleased that has helped you. No tunes. I wanted to focus on the mod on this one. Take care Paul.
Thank you Martyn! Great video.
Thanks you Miguel, Tale care.
👍👍
Thanks Paul. Take care.
I prefer using 10-turn or even 20-turn pots for adding adjustable bias to amplifiers when feasible; knock-off copies of the original tiny blue Bourne trim pots are easily available online nowadays (the ones we used in the audio-repair shop were branded BaoFeng). Anyway, I feel I should echo Martin's concern that adding this adjustable bias circuit from the top, without complete removal of the main board, is NOT a job for newbies to soldering or tube amp repair. The copper foils (that the resistors being clipped out are soldered to) are extremely thin and fragile and are easily delaminated from the board, or the factory solder joints compromised by using too much heat or dwelling too long with the hot soldering iron. If your wire cutters aren't extremely sharp, the blades thin and precise, and if you aren't gentle when straightening the bent stubs of wire, you might break the foils or the solder connection at the underside of the board where you can't see it; and if a connection fails while the amp is being played through, you can measure the life of your tubes and perhaps even the power or output transformer *in mere minutes*. Most people might be better off having a technician add this when they're doing routine service on these amps such as replacing the crappy, known to fail, IC branded electrolytic power supply capacitors.......
Hello. This one didn't have the IC caps in it. From 2019 onward, Fender have changed the bias to Cathode Bias. I think that is a move in the right direction for these amps. Take care.
Does it matter what version the PCB is? Mine is a Blues Jr. IV with a black PCB.
Hello. That's a really good question. I have just done a bit of searching online, and came up with this: www.indystringtheory.com/service/what-version-blues-junior-do-i-have/I have looked at the pictures close up. The black board is indeed different. That board was introduced in 2019. The Blues Junior in this video is a 2018. The customer checked the bias and it was at 85%. The earlier ones were set at 100%. I have yet to see a 2019 onward BJ. 70% is the best setting for the bias. I don't think the mod will fit on a 2019 board. The mod replaces R51 and R52. I can't see either on the black board, though it is a bit blurry when you enlarge the pictures.
You could check the bias using the video? P1, P2, P3 look the same on the black board. Thank you for bringing that one up. Take care.
Hello. I have done a bit more checking. Your amp is Cathode Biased, not fixed biased. So you don't need the mod. I new they had changed over, but I thought it was in the last couple of years. Check the link below. I got there in the end. Take care.
www.tdpri.com/threads/fender-blues-junior-iv-schematic.1104154/
@@vintageguitaramp_guitarteacher Awesome, thanks!
Does the BJ have a 240v tap as well as the 230v it comes with from the factory? Putting that right would help with tube life. I did the swap on my PRRi.
Hello. Sorry this comment slipped by me. Just found it while checking some of the videos. Yes It does have a 240 Volt tap. I changed this one over. I am going to be releasing another Blues Junior video in a few days. I go through the voltage change on that one. Thanks for watching and take care.
Please remove the protective plastic off of your multimeter. You owe that to your subscribers. Very anoying to look at.
Hello. Tim, will do. Thanks for watching and take care.
@@vintageguitaramp_guitarteacher my apologies. That sounded a little harsh. Loved the video. That little bias board is awesome.
Hello Tim, its's okay. I need people to tell me if things are not right. It keeps me on my toes. Thanks Tim and take care.