Some observations: 1.) The chassis appears to have been submerged in a sewage treatment lake, possibly to silence the %@#?*& hum :) 2.) I had a similar hum problem with an Ampeg Jet a couple years ago.....and your grounding analysis provides insight to the cause. 3.) I think this is the best video of yours I have ever watched. Loaded with content and very instructional. Thanks for posting :)
This is a must-see video! Best explanation EVER about ground loops. Brad, your dedication to making this old Ampeg Rocket play well is admirable. Part 3 will be worth the wait!
The fact that we can watch these videos as if we’re sitting at the bench and watching what goes on is pretty amazing. Thank you for doing what you do. I’ve said it before and will probably say it again in the future.
Irrespective of the period taken to restore this Rocket to proper operation, I simply relish the opportunity to attend class at the same time. Your explanation of how to understand voltage behavior was enlightening. It adds credence to the defense of how lengthy troubleshooting can vary on a case by case basis. This amp is part and parcel of that scenario. I can't wait for Ampeg III... This time, it's personal. A very worthwhile trilogy, Mr Brad. Educational, and a show to boot. Keep rockin' sir.
inductive capacitance. experienced this before while shipbuilding in the uK.it involved screened cables passing through metal holes, we were using 240V for our supply voltage. and we were getting 120V to 140V readings from the screen down to earth. the guys were getting electric shocks from these,and the simple solution was earth the screen at one end solved the problem. great show BTW
Your explanation of the ground loop problem ist FANTASTIC! Thanks to this so much! Now the idea of the ground loop switch on a DI Box makes so much sense!
Loved the instructional intermission! I took an electronics theory class in college but its been 10 years now and haven't had much practical application of it so I'm a tad rusty. It all came flooding back to memory watching lol.
I'm not sure if you have this information but, you can get 3/8" Keystone Hard Fibre Shoulder Washers from Mouser (Mouser P/N 534-3069) to isolate 1/4" jacks from the chassis. All you need to do is drill the jack chassis hole out to 3/8" and install one washer on each side of the chassis. Then install the jack through the washers and tighten the nut. They are cheap. I bought a bag of 100 in 2003 when I built my first amp. They were designed for this purpose.
I want to say a big thank you for this video. I have been trying to find the hum-buzz monster for nearly a week on a 1966 Kay model 720. I would guess I am not alone and the only one who ADDs more ground connections trying to quiet the beast. This video helped me immensely. Thanks
Brad - are you 100% sure that the can was original factory? The reason I ask is that the Ampeg grounding scheme actually works very well if and only if the can is mounted with an insulator with no direct connection to ground where it is connected to the chassis. I've worked on dozens of Ampegs of this vintage and that's how most are set up. The can common is connected up to the ground rail on the board and the ONLY place that is connected to chassis ground is at the input jack. That is why the ground bus line is terminated at one of the jacks. This eliminates all ground loop situations. If you replace the cap can with discrete caps or do any other work on the amp, you will introduce the ground loop you experienced. You have to wire everything up through the ground bus. If the amp did not have a fiber insulator between the cap can and chassis, then it's 99% been replace and/or worked on and someone incorrectly removed the insulator and grounded the can to the chassis. A big no-no with these older Ampegs.
@@goodun6081 Yep - had all of those things to varying degrees too. But there is one important basic common topology in many of these amps and that is the single point ground at the jack and the can needs to be lifted from local contact and run into the ground bus. If you ground that can to the chassis (or ground any of the filter caps to the chassis) you are creating the exact ground loop issue Brad is having with this (and his previous Ampeg - same exact issue). Effectively he ended up recreating the topology by isolating the jacks, but BACKWARDS where the single connection to ground is back at the can/filter caps. (Would have been a lot easier to lift the grounds at the filter caps to the ground bus.)
This video was freaking good! I mean... I love all of your stuff Guitologist, but boy this one was a struggle, and you DON'T budge! That's the spirit! Loved it.
Whew! I have four 1960s Ampegs (Jet, Reverbrocket, Reverbrocket II and a Big M-15) and luckily I've never had this happen after converting to 3 prog chord. Good luck on sorting this out. Looking forward to the next video.
Your whiteboard explanation of grounding was awesome. I have struggled with the relationship between circuit and chassis grounding, but you really made it easy to understand. You sir, have a new subscriber.
Hey Brad, hope you know I'm always with you... That was great, BTW. Finally starting to wrap my head around ground loops and the diagnosis was great... can't wait for pt.3 Thanx so very much and... cheers
Brad - I had a re-issue of the Reverberocket (mid 90s) 212R. It was a beast of an amp... hated hauling it. But the clean tone on this amp was so amazing! Really lush reverb that trailed off into spaciousness. The down side, was the ridiculous rattle within the amp that was always present (regardless of channel) at anything above volume 3 and the super weak distortion channel. Worked around the weak distortion with pedals, which it took nicely, but the vibrating rattle was too much to overcome. It needed a float of sorts... we tried all kinds of things. Changing tubes, Tube rings, tightening screws, removing the chassis... finally just gave it to my pops and moved on to a Swart Space Tone, which is my perfect blues amp, but I’m still in search of that clean/Reverb tone the Ampeg offered... We always joked that it weighed 600 lbs... super sold cabinet... that rattle is 100% the fault of the manufacturer.
Yeah Brad, I rebuilt an Ampeg Head a while back that drove me crazy and the only way I was able to control the hum was to experiment with a star grounding scheme which ended up being very successful. Thanks for your continued intructionals. Nice explanation btw on behavior of grounding.
@@TheGuitologist I can't remember if I had to isolate the input jacks but was great experience for me since it was my first project. Take care my brother!!
Awesome way you went about explaining ground looping Brad! I see you haven't pulled any hair out yet. Thanks for the upload man! BTW, like the Ampeg I was also born in 62 but no grounding loops for me. The ground now jumps toward me.
Awesome session Brad! Nice to see even more of your talent and creativity showing up in these vids. The grounding concepts explanation and the illustration method of presenting it was really cool and must have taken quite some effort and planning, thank you for sharing it with us!!! Watching this channel I never fail to learn something new, whether it be a nuance or a larger concept. Kudos!
Great explanation on ground loops! I am working on converting a Bogen CHB-20A to a guitar amp and this helped me with some noise issues. I am new to this so anything helps. Keep up what you are doing!
It is amazing how grounding can be so much trouble through a whole line of electric and electronic equipment. Is there any such thing as too much ground? Apparently not. Thanks for sharing the video.
That ampeg reminds me of some weird car problems faced over the years,defo gotta put on the ol determination hat and not give up,really enjoy your channel dude,learning lots,thanks for sharing!
I guess when you work on Ampeg amps you have to get out your crayons and go to your HAPPY place, you even stayed inside the lines! You made me hungry, with trees and apples, time for pie!
Had one of these type Ampeg chassis that had a really bad ground loop. Turned out the cap can was originally mounted on a phenolic wafer and whoever replaced the cap replaced the phenolic wafer with a metal one thereby creating the loop. Since it would have been a tin of work to undo the cap can and install a non conductive wafer, i was able to find a spot in the black grounding wire that travels up to the input jacks and grounds various stages and split the loop there and remedy the situation. Yes, crazy grounding scheme...
Great video! I put a variable NFB control in my Marshall; along with a few other mods it means I can switch the amp between a tasteful late 60s lead to a rowdy 70s lead easily.
Brad I´m late to the party, this video is priceless, nobody approched the issues of bad ground schemes and ground loops as you did here. You have 127000 subs, (Jan 2022) you deserve more! Sorry English isn´t my main language. Cheers from South Pole, so yes I´m in the world as* :)
The whiteboard lesson was fucking awesome man. As someone with very little knowledge about amplifiers/grounding, this made it super easy to understand for my dumbass brain. Whereas I wouldn't have given a shit otherwise. Hope you decide to still create more content. I saw you got hit with less views recently but keep on truckin' man! We love ya!
I toured in the 60s with a band and 2 of us had Ampeg amps. The Ampegs were more expensive than comp. Fenders. I was told that they were designed without looking at other amp designs and after watching this video I guess that was true. On the road I can tell you that we had less problems with the Ampegs and that they were dead quiet. Our amp tech said that this was because they did not push the out put tubes as hard as Fender. I think that the Porta Flex bass amp speaks for it's self. Where I mostly saw Ampeg guitar amps was in the studio and with Jazz guitarists. Jazz guys loved them because they said that they were mellow and clean. The company designers did not under stand hard driven guitars and players as they emerged. My question is if the grounding design is the problem how were the amps working and very quiet when they were new. Nobody would ever buy a amp with hum issues anywhere near what this amp was exhibiting. Not being a smart ass just wondering. By the way I am a vintage Fender guy now and build custom amp cases.
When I follow the accepted standard for adding a 3-prong grounded power cable, the problems start. They were designed before the 3rd ground prong in the US. Replacing the cap can might have been a factor as well. But this is the way it goes sometimes, you try to keep amps as original as you can while still making them useful tools.
So true about Ampeg making their amps as clean as possible distortion-wise. I've had 3 different Jets from the early years (late 50's to mid 60's) and the newer they got the harder it was to overdrive them
I enjoyed your explanation of grounding and it cleared up some questions I had about the subect (e.g., ground looping), but it begs the question of the cost-benefit of trying to resuscitate an obviously neglected and abused (and probably design-compromised) amp in favor of buying either a working amp of that vintage or a new one. Ampegs were never that good an amp (I’m 68 so I remember!)-except for their bass amps-and were always overshadowed by Fender. Why “Fender-ize” this amp when the real thing is avaliable...
I remember the lengths to which you went to isolate the inputs on the previous Ampeg - using insulating tape and fibre washers on the metal jack sockets. Would it have been easier and more reliable to use plastic jacks that didn't ground to the chassis?
Yes, plastic jacks is an easy solution but they look very incorrect in an amp made in the 60's and they are probably not able to stand that physical violence from guitarists (or guitologists 😁).
@@TheGuitologist I do not like plastic jacks either. But sometimes the ground connection to plug is better than in metal jacks. BTW, I would be very happy if you could read and comment, if possible, my comment about the Mesa S***n amp case. I perhaps had a point if I did not totally misunderstand the situation. (My comments are found in the last episode (Ahab ...). Your videos are very entertaining and educational and I very much enjoy watching them. Thanks.
@ Kevin: no. There is a voltage differential between the jacks' "grounds" and the first gain stage V1a's "ground." That is root cause for this hum. You need to rewire the jacks' grounds so that they are at the same ground potential as V1a's ground-referenced grid, which is R5 in the schematic. This is subtle stuff, but you can only fix it once you understand where the 120Hz hum is coming from: the filter capacitor's ripple current which gets dumped into this design's "ground" wiring. You model this as a voltage source, "Vnoise." Pencil it into the schematic, and then say "how to I counter Vnoise"? Ideally, you need a differential amplifier on the input, but those weren't around in 1962, so compromises have to be made to attenuate the noise. At this point, you run into the argument "but I don't want to change any of the original design"... I.e., "fix it but don't change anything."
I really feel for Brad in these nightmare scenarios. Like he thinks he has it figured out, but there's 18 min left in the video, and you're like "Oh, buddy, this ain't it..." Grounding, you are a cruel mistress. I screw up every amp I build and it's almost always grounding.
Very nice exclamation of ground ing ii have done many rub amp That because of the high impedance of tube noise is alway a problem components theme can generate noise and will a lot of corosen of the chassis it’s best to go to a classic grounding and eliminate all loops and have just one chassis ground this amp stock has several
Very nice instuctional drawings. But I don't fully understand your artwork at 20:15. Are you saying that a yellow penis placed in a square cow can induce a ground loop?
It's a German torque spec. Every grunt is a graduation mark on the Gutentite scale. 1 grunt = Gutentite. 2 grunts = Really Gutentite. 3 grunts = das borken; overgutentite
Recently I have rebuilt an R-12R with the exact same issues: ht secondary shorted, also a bad rectifier tube, leaky capacitors, and the dreadful ground loop that you have been showing. I couldn't understand why Ampeg overlook the grounding problem, and have been wondering maybe is because the amp originally had an ungrounded mains cord, and changing to a grounded cord would create the ground loop ? Thanks for your videos, awesome stuff !
I'm sure this is going to be a great video, love the repair videos. I actually had one of those amps when I was a teen, so even better. My only question is have we seen the last SPF? Say it ain't so....
Hey. Just saw this. Fun to watch. I've been fighting with an old Ampeg M15 - not sure who's winning. Mine hums with no inputs - jacks don't ground input when nothing inserted. How did you isolate the jacks/ Fiber washers?
Curious if when you moved the filter caps to the board if that induced additional noise? Were you able to test the can in the circuit prior to changing a majority of components? I enjoyed your lesson on ground loops. Keep up the good work and enjoy following the channel!
If you want a mechanically quiet transformer, you need to alternate the direction of every single "E shaped" lamination. It looks like that transformer only alternates the direction of the "E shaped" laminations every 5 laminations. Then you need to drive a wedge between the windings and the center leg of the core. The bolts need to be tight. And finally the transformer needs to be vacuum varnished. Unfortunately this rarely happens with consumer grade electronics, such as this transformer.
Cant wait to hear it. Ground loop problem solved, did you get rid of that ticking tube? Its great to see all you do while working on amps. Now I understand why cost of repair can be high. Time and labor adds up when you encounter weird problems!
Hey Brad, what would you recommend for cleaning the volume pot of a stereo reciever? I have a late 80's Kenwood and the volume pot is scratchy and jumpy.
Geez, what a head ache. I do like Ampeg amps and appreciated this chapter in Flieglers 'AMPS!!' book. He mentioned the accordian input being a little fatter sounding and "Today, we plug into the mic input because it distorts easier.I don't think i - or anyone else played thru the guitar input'. I hope you find a way to get this to work as intended. If not, Fender-izing would be cool,,,,tweed. edit, or bf.
The new format is great man. Love the white board explanation, the math help, and the walk-through of the input scheme. I haven't had much free time so I just watched part 1 and 2 today. I kept wondering if this would benefit from separating the preamp and power amp grounding busses, similar to what is recommended when building a Champ or 5E3 deluxe clone (also recommended on the Rob Robinette site). This may not be possible with that Ampeg, or require unreasonable amounts of work, but it was something I was curious about
I abandoned my J12-D because it needed 6BK11 Compactron tubes which I could not find anywhere. Now I'm entertaining the idea of gutting it, punching another hole in the chassis and using 3 6SL7's as preamp, tremolo and inverter. Perhaps also changing the 7868's to 6V6. I love the sound of Ampegs, but their use of weird "Unobtanium" tubes is enough to make you tear your hair out. Look up 6BK11 in your RCA book. 3 sets of elements in one bottle.
Hi Brad. I may have missed something here but did you try replacing the 5M6 resistor? Also, with the buzzing transformer, you might have tried painting the windings of the power transformer with lots of clear laquer, like 'estapol' or similar. Lots, so that it kind of capillaries itself into & between the winding layers. This worked for me with a little 40 watt transistor amp I built years ago.
Seems like Ampeg wanted the chassis ground from the Input jacks. Maybe the can capacitor isn’t supposed to be chassis grounded, and the line voltage wasn’t meant to reference ground either.
This comment is probably not much use by now but I'll share my experience anyway. First of all. Over the years I've had two power transformers that buzzed under load. One was a beautiful art deco Kenyon that I pulled from a Hamfest score. It lived in my preamp power supply for 20 years until last year. I had that power supply a good 10 feet away from my preamp so I just lived with it until I replaced it with a new one (I couldn't take it anymore!!) The second one was in a priceless "Black Flag" 100W 1967 Marshall Super Lead plexi head. That was a bummer.... There was nothing that could be done except sell that amp to Mick Mars.... Some transformers are just like this. You don't know until you install the thing. Better to not mess around with some old iron and just buy new. Second. I love old Ampeg amps. But damn they eat up a lot of bench time. I'm watching a colleague suffer the same problem with one from this era. I'm pretty much retired from this now but when I was working a lot there were some amps that I just said no to. I like a good challenge but life is too short for lemons! Great video! Thanks!
Mains TX properly isolated from chassis? I know with input jacks I always make sure they are grounded directly to each other with a short length of bus wire.
Well I stood in the middle of the street naked and screamed that this was the best channel on YT ! But it didn’t work. I just got to spend the night with a drag queen named Bubba !!!!!!! My wife was pissed she almost got Bubba out and left me there. JK. Hope things are getting better. 😎🎸🎶✌️🤟
Some observations: 1.) The chassis appears to have been submerged in a sewage treatment lake, possibly to silence the %@#?*& hum :) 2.) I had a similar hum problem with an Ampeg Jet a couple years ago.....and your grounding analysis provides insight to the cause. 3.) I think this is the best video of yours I have ever watched. Loaded with content and very instructional. Thanks for posting :)
That means everything coming from you, Doug. Thanks for all you do to advance this type of content on RUclips, sir.
aw, I love it when the family hugs.
Great comment UD! Nice seeing you here. :)
@@danmick8645 yeah gives you the warm & fuzzies :)
@@TheGuitologist Uncle Doug and Cousin Brad does have a ring to it ;-)))
This is a must-see video! Best explanation EVER about ground loops. Brad, your dedication to making this old Ampeg Rocket play well is admirable. Part 3 will be worth the wait!
The fact that we can watch these videos as if we’re sitting at the bench and watching what goes on is pretty amazing. Thank you for doing what you do. I’ve said it before and will probably say it again in the future.
Well after this, no one can say you are not grounded Brad
Tell that to my wife.
@@TheGuitologist If only women were wired the same as Ampeg's
@@freepress8451 I'd say they are!
Irrespective of the period taken to restore this Rocket to proper operation, I simply relish the opportunity to attend class at the same time. Your explanation of how to understand voltage behavior was enlightening. It adds credence to the defense of how lengthy troubleshooting can vary on a case by case basis. This amp is part and parcel of that scenario. I can't wait for Ampeg III... This time, it's personal. A very worthwhile trilogy, Mr Brad. Educational, and a show to boot. Keep rockin' sir.
inductive capacitance. experienced this before while shipbuilding in the uK.it involved screened cables passing through metal holes, we were using 240V for our supply voltage. and we were getting 120V to 140V readings from the screen down to earth. the guys were getting electric shocks from these,and the simple solution was earth the screen at one end solved the problem. great show BTW
Your explanation of the ground loop problem ist FANTASTIC! Thanks to this so much! Now the idea of the ground loop switch on a DI Box makes so much sense!
Loved the instructional intermission! I took an electronics theory class in college but its been 10 years now and haven't had much practical application of it so I'm a tad rusty. It all came flooding back to memory watching lol.
I'm not sure if you have this information but, you can get 3/8" Keystone Hard Fibre Shoulder Washers from Mouser (Mouser P/N 534-3069) to isolate 1/4" jacks from the chassis. All you need to do is drill the jack chassis hole out to 3/8" and install one washer on each side of the chassis. Then install the jack through the washers and tighten the nut. They are cheap. I bought a bag of 100 in 2003 when I built my first amp. They were designed for this purpose.
BTW- probably the best visual description ever about ground loops!
I want to say a big thank you for this video. I have been trying to find the hum-buzz monster for nearly a week on a 1966 Kay model 720. I would guess I am not alone and the only one who ADDs more ground connections trying to quiet the beast. This video helped me immensely. Thanks
Let’s keep those old amps alive, guys like you and Uncle Doug great video.
If i could just like this 10 times i would, just for the explanation s with the whiteboard/crayon alone.
i was the clearest ive ever been explained grounding
Brad - are you 100% sure that the can was original factory? The reason I ask is that the Ampeg grounding scheme actually works very well if and only if the can is mounted with an insulator with no direct connection to ground where it is connected to the chassis. I've worked on dozens of Ampegs of this vintage and that's how most are set up. The can common is connected up to the ground rail on the board and the ONLY place that is connected to chassis ground is at the input jack. That is why the ground bus line is terminated at one of the jacks.
This eliminates all ground loop situations. If you replace the cap can with discrete caps or do any other work on the amp, you will introduce the ground loop you experienced. You have to wire everything up through the ground bus.
If the amp did not have a fiber insulator between the cap can and chassis, then it's 99% been replace and/or worked on and someone incorrectly removed the insulator and grounded the can to the chassis. A big no-no with these older Ampegs.
@@goodun6081 Yep - had all of those things to varying degrees too. But there is one important basic common topology in many of these amps and that is the single point ground at the jack and the can needs to be lifted from local contact and run into the ground bus. If you ground that can to the chassis (or ground any of the filter caps to the chassis) you are creating the exact ground loop issue Brad is having with this (and his previous Ampeg - same exact issue).
Effectively he ended up recreating the topology by isolating the jacks, but BACKWARDS where the single connection to ground is back at the can/filter caps. (Would have been a lot easier to lift the grounds at the filter caps to the ground bus.)
This video was freaking good! I mean... I love all of your stuff Guitologist, but boy this one was a struggle, and you DON'T budge! That's the spirit! Loved it.
Oh, and the montage in the middle, explaining "Ground" was exquisite, congrats! Lots of work went into that one, thanks!
Enjoyed the white board lesson....thanks
Dude! Loving this series. Also really dig the whiteboard session on ground loops, makes it super clear what's going on!
Whew! I have four 1960s Ampegs (Jet, Reverbrocket, Reverbrocket II and a Big M-15) and luckily I've never had this happen after converting to 3 prog chord. Good luck on sorting this out. Looking forward to the next video.
God damn, that "Grounding" whiteboard explanation was excellent.
Your whiteboard explanation of grounding was awesome. I have struggled with the relationship between circuit and chassis grounding, but you really made it easy to understand. You sir, have a new subscriber.
Very informative, you explain things where a layman can easily grasp your explanation. Thanks Brad.
can i thumb up a vid 2x? that informative section was the clearest explanation of grounding i was ever offered. and i even went to trade school
Hey Brad, hope you know I'm always with you...
That was great, BTW. Finally starting to wrap my head around ground loops
and the diagnosis was great... can't wait for pt.3
Thanx so very much and...
cheers
Thank you for your clear explanation of ground loops. This is something that has always confused me. I think I finally understand.
Brad - I had a re-issue of the Reverberocket (mid 90s) 212R. It was a beast of an amp... hated hauling it. But the clean tone on this amp was so amazing! Really lush reverb that trailed off into spaciousness. The down side, was the ridiculous rattle within the amp that was always present (regardless of channel) at anything above volume 3 and the super weak distortion channel. Worked around the weak distortion with pedals, which it took nicely, but the vibrating rattle was too much to overcome.
It needed a float of sorts... we tried all kinds of things. Changing tubes, Tube rings, tightening screws, removing the chassis... finally just gave it to my pops and moved on to a Swart Space Tone, which is my perfect blues amp, but I’m still in search of that clean/Reverb tone the Ampeg offered...
We always joked that it weighed 600 lbs... super sold cabinet... that rattle is 100% the fault of the manufacturer.
Try a stethoscope?
Death Rattle confirmed😂
Yeah Brad, I rebuilt an Ampeg Head a while back that drove me crazy and the only way I was able to control the hum was to experiment with a star grounding scheme which ended up being very successful. Thanks for your continued intructionals. Nice explanation btw on behavior of grounding.
Glad I ain't the only one.
@@TheGuitologist I can't remember if I had to isolate the input jacks but was great experience for me since it was my first project. Take care my brother!!
Awesome way you went about explaining ground looping Brad! I see you haven't pulled any hair out yet. Thanks for the upload man! BTW, like the Ampeg I was also born in 62 but no grounding loops for me. The ground now jumps toward me.
Awesome session Brad! Nice to see even more of your talent and creativity showing up in these vids. The grounding concepts explanation and the illustration method of presenting it was really cool and must have taken quite some effort and planning, thank you for sharing it with us!!! Watching this channel I never fail to learn something new, whether it be a nuance or a larger concept. Kudos!
Back in my feed it’s perplexing!
I had a ‘55 Gibson GA-9 where everything was grounded to the input jack. It was extremely quiet, hum-wise. But that was the only ground point.
Excellent explanation of ground loops. I felt like I was back in Grade 13 physics!
Excellent grounding explanation Brad,I hope tinkerers watch it and learn.Top teaching marks professor!
Great explanation on ground loops! I am working on converting a Bogen CHB-20A to a guitar amp and this helped me with some noise issues. I am new to this so anything helps. Keep up what you are doing!
"The Problem Solver". Enjoyed it as alway Brad....
I've said this before but Ampegs are the work of satan. The old and the new.
This video is golden.
It is amazing how grounding can be so much trouble through a whole line of electric and electronic equipment. Is there any such thing as too much ground? Apparently not. Thanks for sharing the video.
now that's a high quality upload for 1962.
That ampeg reminds me of some weird car problems faced over the years,defo gotta put on the ol determination hat and not give up,really enjoy your channel dude,learning lots,thanks for sharing!
Given the severe oxidation on those input jacks, wouldn't it be better to swap those out with brand new, grounded Switchcraft jacks?
switchcraft.com/Category_Multi.aspx?Parent=952
I guess when you work on Ampeg amps you have to get out your crayons and go to your HAPPY place, you even stayed inside the lines! You made me hungry, with trees and apples, time for pie!
You said a mouthful there. :D
Great video Brad can’t wait to hear this baby sing
Great video! Can't wait to see part 3 where you show the results of all your hard work by playing us a tune on that Ampeg.
Great video Brad. I'm new to this, so I really appreciated the whiteboard lesson. Feel much more "grounded" now. Have a nice weekend.
Man this restoration IS a real head scratcher !! Best of luck and look forward to part 3, cheers!!
Thanks Brad! Nice grounding tutorial also!
Had one of these type Ampeg chassis that had a really bad ground loop.
Turned out the cap can was originally mounted on a phenolic wafer and whoever replaced the cap replaced the phenolic wafer with a metal one thereby creating the loop.
Since it would have been a tin of work to undo the cap can and install a non conductive wafer, i was able to find a spot in the black grounding wire that travels up to the input jacks and grounds various stages and split the loop there and remedy the situation.
Yes, crazy grounding scheme...
Great video! I put a variable NFB control in my Marshall; along with a few other mods it means I can switch the amp between a tasteful late 60s lead to a rowdy 70s lead easily.
Fantastic tutorial on ground loops! The result is well worth the efforts imo.
Seriously Brad, do more whiteboard stuff.
Thanks so much for the lesson on grounding and ground loops, Etc.
Hey I'm not getting notifications but, strangely enough.. you're popping in at the top of my feed for the first time.
Thought I'd mention that.
Brad I´m late to the party, this video is priceless, nobody approched the issues of bad ground schemes and ground loops as you did here. You have 127000 subs, (Jan 2022) you deserve more! Sorry English isn´t my main language. Cheers from South Pole, so yes I´m in the world as* :)
The whiteboard lesson was fucking awesome man. As someone with very little knowledge about amplifiers/grounding, this made it super easy to understand for my dumbass brain. Whereas I wouldn't have given a shit otherwise. Hope you decide to still create more content. I saw you got hit with less views recently but keep on truckin' man! We love ya!
Awesome video Brad ty ty ty
I toured in the 60s with a band and 2 of us had Ampeg amps. The Ampegs were more expensive than comp. Fenders. I was told that they were designed without looking at other amp designs and after watching this video I guess that was true. On the road I can tell you that we had less problems with the Ampegs and that they were dead quiet. Our amp tech said that this was because they did not push the out put tubes as hard as Fender. I think that the Porta Flex bass amp speaks for it's self. Where I mostly saw Ampeg guitar amps was in the studio and with Jazz guitarists. Jazz guys loved them because they said that they were mellow and clean. The company designers did not under stand hard driven guitars and players as they emerged. My question is if the grounding design is the problem how were the amps working and very quiet when they were new. Nobody would ever buy a amp with hum issues anywhere near what this amp was exhibiting. Not being a smart ass just wondering. By the way I am a vintage Fender guy now and build custom amp cases.
When I follow the accepted standard for adding a 3-prong grounded power cable, the problems start. They were designed before the 3rd ground prong in the US. Replacing the cap can might have been a factor as well. But this is the way it goes sometimes, you try to keep amps as original as you can while still making them useful tools.
So true about Ampeg making their amps as clean as possible distortion-wise. I've had 3 different Jets from the early years (late 50's to mid 60's) and the newer they got the harder it was to overdrive them
I enjoyed your explanation of grounding and it cleared up some questions I had about the subect (e.g., ground looping), but it begs the question of the cost-benefit of trying to resuscitate an obviously neglected and abused (and probably design-compromised) amp in favor of buying either a working amp of that vintage or a new one. Ampegs were never that good an amp (I’m 68 so I remember!)-except for their bass amps-and were always overshadowed by Fender. Why “Fender-ize” this amp when the real thing is avaliable...
Wait for the demo. You might change your tune. ;)
Best video yet. The hand drawn explanation was totally awesome.
A good sadistic video of the misery of chasing oscillations.
I remember the lengths to which you went to isolate the inputs on the previous Ampeg - using insulating tape and fibre washers on the metal jack sockets. Would it have been easier and more reliable to use plastic jacks that didn't ground to the chassis?
That would be one way to go, but I detest plastic jacks.
@kevin paul halliday Tried that off cam, didn't work.
Yes, plastic jacks is an easy solution but they look very incorrect in an amp made in the 60's and they are probably not able to stand that physical violence from guitarists (or guitologists 😁).
@@TheGuitologist I do not like plastic jacks either. But sometimes the ground connection to plug is better than in metal jacks.
BTW, I would be very happy if you could read and comment, if possible, my comment about the Mesa S***n amp case. I perhaps had a point if I did not totally misunderstand the situation. (My comments are found in the last episode (Ahab ...).
Your videos are very entertaining and educational and I very much enjoy watching them. Thanks.
@ Kevin: no. There is a voltage differential between the jacks' "grounds" and the first gain stage V1a's "ground." That is root cause for this hum. You need to rewire the jacks' grounds so that they are at the same ground potential as V1a's ground-referenced grid, which is R5 in the schematic. This is subtle stuff, but you can only fix it once you understand where the 120Hz hum is coming from: the filter capacitor's ripple current which gets dumped into this design's "ground" wiring. You model this as a voltage source, "Vnoise." Pencil it into the schematic, and then say "how to I counter Vnoise"? Ideally, you need a differential amplifier on the input, but those weren't around in 1962, so compromises have to be made to attenuate the noise. At this point, you run into the argument "but I don't want to change any of the original design"... I.e., "fix it but don't change anything."
I really feel for Brad in these nightmare scenarios. Like he thinks he has it figured out, but there's 18 min left in the video, and you're like "Oh, buddy, this ain't it..."
Grounding, you are a cruel mistress. I screw up every amp I build and it's almost always grounding.
Very nice exclamation of ground ing ii have done many rub amp That because of the high impedance of tube noise is alway a problem components theme can generate noise and will a lot of corosen of the chassis it’s best to go to a classic grounding and eliminate all loops and have just one chassis ground this amp stock has several
I got the notification on this one, Brad. Don't know what's going on but this time you popped up.
I'm glad to hear they have not forsaken lil ol me entirely. Thanks for the feedback.
Tim, I see a "that's what she said" joke in there.
Was all well above my head but your dedication to getting amp right is awesome bro. All the best from NZ
Very nice instuctional drawings. But I don't fully understand your artwork at 20:15. Are you saying that a yellow penis placed in a square cow can induce a ground loop?
PHILISTINE!!! That's clearly a pregnant honey badger. :D
@@TheGuitologist Even so, wouldn't that create a different sort of sound?
That clicking sounds like an old car engine! That amp has NOISY VALVES! See what I did there? LOL! 😂😂😂
It's a German torque spec. Every grunt is a graduation mark on the Gutentite scale. 1 grunt = Gutentite. 2 grunts = Really Gutentite. 3 grunts = das borken; overgutentite
To confirm grounding problems, check for zero ohms with an ohmmeter, or use a wire to connect the grounds to see if it makes a difference.
Awesome video this time, loved the drawings. This ought to get a million views!
That was awesome Brad!!! I learned a WHOLE BUNCH of new stuff from this vid!... Thanks buddy and keep up the amazing work.
Recently I have rebuilt an R-12R with the exact same issues: ht secondary shorted, also a bad rectifier tube, leaky capacitors, and the dreadful ground loop that you have been showing. I couldn't understand why Ampeg overlook the grounding problem, and have been wondering maybe is because the amp originally had an ungrounded mains cord, and changing to a grounded cord would create the ground loop ? Thanks for your videos, awesome stuff !
yo I love what you did with the white board, your videos are actually amazing I watch them instead of tv this is the shit
Love the drawing. Made a lot of sense.
I'm sure this is going to be a great video, love the repair videos. I actually had one of those amps when I was a teen, so even better. My only question is have we seen the last SPF? Say it ain't so....
Will you replace the 5.6M resistor? (Thanks for the ground loop visuals.)
No, I rewired the jacks to Fender specs, except I left the 47K values on the input resistors.
Hey. Just saw this. Fun to watch. I've been fighting with an old Ampeg M15 - not sure who's winning. Mine hums with no inputs - jacks don't ground input when nothing inserted. How did you isolate the jacks/ Fiber washers?
Curious if when you moved the filter caps to the board if that induced additional noise? Were you able to test the can in the circuit prior to changing a majority of components?
I enjoyed your lesson on ground loops. Keep up the good work and enjoy following the channel!
Sometimes someone's grunting is very enlightening to learn this interesting issues about ground loops.
If you want a mechanically quiet transformer, you need to alternate the direction of every single "E shaped" lamination. It looks like that transformer only alternates the direction of the "E shaped" laminations every 5 laminations. Then you need to drive a wedge between the windings and the center leg of the core. The bolts need to be tight. And finally the transformer needs to be vacuum varnished. Unfortunately this rarely happens with consumer grade electronics, such as this transformer.
Cant wait to hear it. Ground loop problem solved, did you get rid of that ticking tube? Its great to see all you do while working on amps. Now I understand why cost of repair can be high. Time and labor adds up when you encounter weird problems!
@15:00 The first thing we learned in Spaghetti 101 is that you also need more wires..."Hey Moe, hey Larry these pipes are full of wires"
Divin' hot in a tube amp, love it!
Hey Brad, what would you recommend for cleaning the volume pot of a stereo reciever? I have a late 80's Kenwood and the volume pot is scratchy and jumpy.
This is what I use on pots and faders: amzn.to/2YiLWVF
21:56 That orange tipped handle screwdriver, I have two of those. Got them at Walmart like 15 years ago and am still using them.
Geez, what a head ache. I do like Ampeg amps and appreciated this chapter in Flieglers 'AMPS!!' book. He mentioned the accordian input being a little fatter sounding and "Today, we plug into the mic input because it distorts easier.I don't think i - or anyone else played thru the guitar input'. I hope you find a way to get this to work as intended. If not, Fender-izing would be cool,,,,tweed. edit, or bf.
Ps: i like the vid. I'm gonna try to apply what you showed to this sound city plaguing me
Commitment to getting it right, love it!
The new format is great man. Love the white board explanation, the math help, and the walk-through of the input scheme. I haven't had much free time so I just watched part 1 and 2 today. I kept wondering if this would benefit from separating the preamp and power amp grounding busses, similar to what is recommended when building a Champ or 5E3 deluxe clone (also recommended on the Rob Robinette site). This may not be possible with that Ampeg, or require unreasonable amounts of work, but it was something I was curious about
I abandoned my J12-D because it needed 6BK11 Compactron tubes which I could not find anywhere. Now I'm entertaining the idea of gutting it, punching another hole in the chassis and using 3 6SL7's as preamp, tremolo and inverter. Perhaps also changing the 7868's to 6V6.
I love the sound of Ampegs, but their use of weird "Unobtanium" tubes is enough to make you tear your hair out.
Look up 6BK11 in your RCA book. 3 sets of elements in one bottle.
Hi Brad. I may have missed something here but did you try replacing the 5M6 resistor? Also, with the buzzing transformer, you might have tried painting the windings of the power transformer with lots of clear laquer, like 'estapol' or similar. Lots, so that it kind of capillaries itself into & between the winding layers. This worked for me with a little 40 watt transistor amp I built years ago.
Seems like Ampeg wanted the chassis ground from the Input jacks. Maybe the can capacitor isn’t supposed to be chassis grounded, and the line voltage wasn’t meant to reference ground either.
Nope. A capacitor only fixes DC issues. This is clearly an AC-issue, 120 Hz.
That tube sounds like a Timex watch ad from the late 70’s. Takes a licken’ and keeps in ticken’
This comment is probably not much use by now but I'll share my experience anyway.
First of all. Over the years I've had two power transformers that buzzed under load. One was a beautiful art deco Kenyon that I pulled from a Hamfest score. It lived in my preamp power supply for 20 years until last year. I had that power supply a good 10 feet away from my preamp so I just lived with it until I replaced it with a new one (I couldn't take it anymore!!)
The second one was in a priceless "Black Flag" 100W 1967 Marshall Super Lead plexi head. That was a bummer.... There was nothing that could be done except sell that amp to Mick Mars....
Some transformers are just like this. You don't know until you install the thing. Better to not mess around with some old iron and just buy new.
Second. I love old Ampeg amps. But damn they eat up a lot of bench time. I'm watching a colleague suffer the same problem with one from this era. I'm pretty much retired from this now but when I was working a lot there were some amps that I just said no to. I like a good challenge but life is too short for lemons!
Great video! Thanks!
I've grounded many amps, especially high gain, at the input jack and they are dead quiet. As that ground is the ONLY signal ground to the chassis.
Didn’t get the notification and I’m subscribed. Very strange
You almost have to click the bell anymore, and even that's no guarantee.
Love
That
Ewe-toob
Shadow Banning ! 🤪
Mains TX properly isolated from chassis? I know with input jacks I always make sure they are grounded directly to each other with a short length of bus wire.
Well I stood in the middle of the street naked and screamed that this was the best channel on YT !
But it didn’t work. I just got to spend the night with a drag queen named Bubba !!!!!!! My wife was pissed she almost got Bubba out and left me there.
JK. Hope things are getting better.
😎🎸🎶✌️🤟
good 'un lmao.
My oh my what a tricky amp design, well you surely deserved a good break !
I Didn’t get the notification either and I’m subscribed.
Make sure you've clicked the bell beside the "subscribe" button. Still won't guarantee you get notified, but might help. Thanks for watching!
Yeah, Dig that high speed whiteboard!!! But did you know, Gravity is Magnetism !! 🤖
dude, thanks so much for that grounding lesson...i'm fucking awakened dude, i get it now! woohoo! haha cheers