A detailed demo on how to safely bias your Marshall Plexi or similar tube amp head. This will definitely help you to respect but not fear going into your amp and changing the tubes and bias!
My God FINALLY a video that actually helps a fellow human being and isn't about the demonstrator talking about himself or leaving out 50 steps .BEST VIDEO EVER .only VIDEO ON UA-cam.
So, going from EL34 to KT66, didn't you have to change the bias resistor, and add that "follower" resistor and such? Or did you only have to change the bias as you showed?
I just bought 4 Mullard EL34 matched quads for my original 1959 Marshall Super Lead 100 (1968-9?). Also a bias probe. The instructions say,"This Bias Tester measures Pin3 Plate current on EL34...etc". So why are you using 2 meters to check Pin3 ? Why not switch the meter with your bias probe to DCV to read your 460V ? Then switch it back to MA for your adjustment.Or am I missing something here?
Im using two meters so I don't have to switch the meter from one use to the other so it makes the video demo quicker. I pre set up the other so all I had to do was switch to it to continue the demo if that makes sense
Hello. I have the Marshall ma50h. Just put in JJ el34. One tube is reading in mv. The other tube is over 200. I switched it volts and got a normal reading. I'm using the pins on com5 on the board not a socket tester. Any suggestions ?
yes you could check the other side as well, but after biasing this amp so many times in the past I found that all 4 stay really close every time I bias a single position so I didn't want to the the time to film me switching and checking another position but you certainly can switch the probe to the other positions and take your readings again to check how close they are.
If the head had not connected to the cabinet or load box and had i turned on the Power and turned on standby switch without any input ,what would It have been happened?
@@roycox4415 thanks a lot man.i would like play loud beacuse the valve's sound is reach of armonic and also hot sound but i can't do it.if i leave the maximum value of gain and volume and i put a variac between output jcm900 to cabinet 1960a, is it dangerous for head amp or cabinet?
@@roycox4415 you know if is it possible to put varicac to supply the final valves(5881) with less voltage for changing headroom and dreaming have a better sound without high gain-volume (similar like van halen)?
you know if is it possible to put varicac to supply the final valves(5881) with less voltage for changing headroom and dreaming have a better sound without high gain-volume (similar like van halen)? @@roycox4415 or put variac between output of jcm900 to cabinet 1960a is it dangerous? i'd like to have sound like when i left maximum value of gain and volume is amazing and reach of armonic frequency, but of course i can't do it cause neighbor..how can i have that sount with low volume?
Yes because the amp has to be completely on. Never turn your head on without a speaker load, whether it be a load box or plugged into the actual cabinet! Very important!
If you look at the socket from the bottom, look for the key (the slot or notch that guides the tube in position) From the underside of the socket, pin 1 is the first pin clockwise from that key. Follow that formula around and you then can find the rest of the numbered pin slots. Just remember that when you look at the socket from the bottom that it's reversed from what it looks like from the top, if that makes sense. Find the guide slot and count three pins clockwise from the underside. I tried t make that explanation detailed but let me know if you are confused and I can try and help more. Be careful and don't touch anything with your fingers or metal tools. Always assume that everything under that chassis is harmful and if you still feel very unsure, then take the amp to a tech. Safe over sorry!
+Matan Elmalem yes when looking at the tube socket from the underside of the chassis. If you are counting from the top side of the chassis then you need to find the guide slot and count three pins counterclockwise. Watch the section of the video where I show exactly how to find pin three. It shows me pointing out, in detail, where it is from the underside of the chassis.
All of the tubes have a pin three but the one mentioned in the video and the one you look for to test the plate voltage is any of the power tubes pin three. Power tubes are the big tubes if you are not sure. Your socket, from the bottom view will be numbered most likely. Look for number 3. Watch the video and I show you how I find it and what it looks like on this amp!
I also have a vintage 1973 "Rosary" 100W. LIke your master volume cause God knows you need it. You might want to mention these things are super heavy and they are unbalanced.
My God FINALLY a video that actually helps a fellow human being and isn't about the demonstrator talking about himself or leaving out 50 steps .BEST VIDEO EVER .only VIDEO ON UA-cam.
the best,better and only video that explains in the simpest way how to do it! and I also understood everything, since I'm italian...well done!
Thank you so much! So glad it helped you out! Be safe and have fun.
This was really a terrific help. Thanks so much for a clear, well-paced and informative video. Truly appreciated. :)
Cheers Roy, this is excellent you have saved me a tonne of money. Good man.
So, going from EL34 to KT66, didn't you have to change the bias resistor, and add that "follower" resistor and such? Or did you only have to change the bias as you showed?
I just bought 4 Mullard EL34 matched quads for my original 1959 Marshall Super Lead 100 (1968-9?).
Also a bias probe.
The instructions say,"This Bias Tester measures Pin3 Plate current on EL34...etc".
So why are you using 2 meters to check Pin3 ?
Why not switch the meter with your bias probe to DCV to read your 460V ?
Then switch it back to MA for your adjustment.Or am I missing something here?
Im using two meters so I don't have to switch the meter from one use to the other so it makes the video demo quicker. I pre set up the other so all I had to do was switch to it to continue the demo if that makes sense
@@roycox4415 Eurotubes makes a bias probe that reads both the ma from the tube and the volts from the plate voltage at the same time. Solid purchase!
Hi gorgeous video ! I'm wondering if i adjusted Bias only the First valve el34 or would i have to repeat this adjusting for all el34 valves?
great video mate, best ive seen on biasing :)
Thanks so much ! Glad it helped you out!
Hello. I have the Marshall ma50h. Just put in JJ el34. One tube is reading in mv. The other tube is over 200. I switched it volts and got a normal reading. I'm using the pins on com5 on the board not a socket tester. Any suggestions ?
Great video! Blue Towers of Death! Never put both hands in an amp! Accidentally connect yourself to the hereafter or it feels that way.
Hi, do i need to have the load box be powered on to get the fonction of matching impedance working ?
Which setting should the multimeter be on for the bias probe, I'm not getting decimal values, thanks.
It shows you in the video! Should be milliamps
It will say Ma on your meter
When finding plate voltage you want to use DC Volts only!!!
Shouldn't you check the the voltage drop across each tube's cathode resister?
You only have to do one tube? How do you know one side isn't hotter then the other?
yes you could check the other side as well, but after biasing this amp so many times in the past I found that all 4 stay really close every time I bias a single position so I didn't want to the the time to film me switching and checking another position but you certainly can switch the probe to the other positions and take your readings again to check how close they are.
If the head had not connected to the cabinet or load box and had i turned on the Power and turned on standby switch without any input ,what would It have been happened?
you can do damage to the entire amp but most likely the transformers.
@@roycox4415 thanks a lot man.i would like play loud beacuse the valve's sound is reach of armonic and also hot sound but i can't do it.if i leave the maximum value of gain and volume and i put a variac between output jcm900 to cabinet 1960a, is it dangerous for head amp or cabinet?
@@roycox4415 you know if is it possible to put varicac to supply the final valves(5881) with less voltage for changing headroom and dreaming have a better sound without high gain-volume (similar like van halen)?
you know if is it possible to put varicac to supply the final valves(5881) with less voltage for changing headroom and dreaming have a better sound without high gain-volume (similar like van halen)?
@@roycox4415 or put variac between output of jcm900 to cabinet 1960a is it dangerous? i'd like to have sound like when i left maximum value of gain and volume is amazing and reach of armonic frequency, but of course i can't do it cause neighbor..how can i have that sount with low volume?
Great video. Thanks.
Thanks so much for taking the time to check it out. Hope it helped a bit!
did you change some of your coupling caps the brown ones
some of the caps may have been changed when the amp underwent a master volume mod before i purchased it.
I need to search for the Max dissipation Watts on my type of Tubes?
yes, its super easy to find online and all tubes have a recommended value for that
Roy Cox Thanks Bro!!
I need to connect the speaker (1960ahw) to the back of the amp with a speaker cable while checking the plate voltage?
Yes because the amp has to be completely on. Never turn your head on without a speaker load, whether it be a load box or plugged into the actual cabinet! Very important!
+Roy Cox Thanks Bro!! one more thing, I don't have an alligator clip can I put the black normal cable in the screw chassis hole?
+Matan Elmalem yes make sure it's very secure
+Roy Cox cool and I can use one multimeter for the job right?
??
If I don't have Numbers on the Tube Sockets how do I find Pin 3?
If you look at the socket from the bottom, look for the key (the slot or notch that guides the tube in position) From the underside of the socket, pin 1 is the first pin clockwise from that key. Follow that formula around and you then can find the rest of the numbered pin slots. Just remember that when you look at the socket from the bottom that it's reversed from what it looks like from the top, if that makes sense. Find the guide slot and count three pins clockwise from the underside. I tried t make that explanation detailed but let me know if you are confused and I can try and help more. Be careful and don't touch anything with your fingers or metal tools. Always assume that everything under that chassis is harmful and if you still feel very unsure, then take the amp to a tech. Safe over sorry!
+Roy Cox Thanks for the Fast Response!!! the Bottom? you mean from the PCB Board?
+Roy Cox Thanks for all the Help Bro!!
the other cable I just put on one of the screw holes just for ground?
+Matan Elmalem yes when looking at the tube socket from the underside of the chassis. If you are counting from the top side of the chassis then you need to find the guide slot and count three pins counterclockwise. Watch the section of the video where I show exactly how to find pin three. It shows me pointing out, in detail, where it is from the underside of the chassis.
+Roy Cox and for Ground just to put the Cable in one of the Screw holes on the Chassis?
where is Pin 3 Located? on which Tube?
All of the tubes have a pin three but the one mentioned in the video and the one you look for to test the plate voltage is any of the power tubes pin three. Power tubes are the big tubes if you are not sure. Your socket, from the bottom view will be numbered most likely. Look for number 3. Watch the video and I show you how I find it and what it looks like on this amp!
+Roy Cox Thanks a Lot Bro!!
how do I Know how much my tube rated for the maximum watts?
You have to google the type of tube and you'll see it listed somewhere
I see its 25. Ive set mine on 38, its 3 mA more then the recommended. is that ok?
wow great explanation but still am afraid to do it
I also have a vintage 1973 "Rosary" 100W. LIke your master volume cause God knows you need it. You might want to mention these things are super heavy and they are unbalanced.
I do actually in the beginning when I talk about supporting it after it pulled from chassis!