@@stuartukguitarampguy5830 Marshall have been doing that to their DI outputs since the seventies Stuart. Seems to work well too 😁 Nice video my friend.
@@DrWatts-bi1jv , you'll find 10 ohm ground-lift resistors in some solid-state hifi power amps as well, Adcom amps in particular. If the system has a ground loop in combination with the other components, the 10 ohm resistors will (maybe, hopefully) burn open in order to save you from burning foil traces on the circuit board. Whenever I worked on one of those amplifiers, the ground lift resistors, and the bleed resisters across the main filter caps, are the 1st things I would check. (Those amps are also infamous for horrid capacitor leakage that looks like tobacco juice, smells like dead fish, corrodes component leads and solder joints, and makes the PC board conductive; fixing that mess is a big job!). Some pro-sound power amplifiers ---- UREI comes to mind ---- had a set of screw terminals on the rear panel where you could remove a jumper in order to separate the audio ground from the always-earth-grounded chassis, or install a resistor between them, to cure ground loops.
Excellent video... I have to replace one of the effects loop jacks on my 25555 as I'm getting a intermittent power drop from time to time.. how do I know which one to replace if I do not have testing equipment like yours?
First make absolutely sure it's the jacks by linking them together with a short patch lead. If you get the problem in that configuration it's not the jacks. If you're 100% sure it's the jacks, just replace both.
It's called Tinner Copper Wire or TC wire and comes in various guages called swg - standard wire guage. I use 16swg and 20swg. Of course, if you have any gash cable with solid copper cores of about the right diameter you can just strip it back and use that..
Yes definitely, but you'll note I was scratching my head about exactly that throughout the rest of the vid. ANd it COULD have been something to do with the V2b stage.
At 26:30, that "sprung" leaf switch, not making contact, could be from somebody with poor soldering skills; too much heat applied for too long to the terminal, while pushing down on it with the soldering-iron tip, likely softened the plastic housing, allowing the contact to push down and away from its normally-closed, at-rest, position ---- and when the plastic cooled and hardened, the contact remained in a misaligned position. (The jack was probably bolted to the chassis first before soldering, which would help explain the erstwhile "technician" failing to see not only the permanently-open switching contacts but also that he didn't properly solder one wire). I've seen a somewhat similar thing happen when inserting this type of jack into a PC board with really tight, too small holes, pushing the terminals up and away from their normal, at rest position, causing poor tensioning of the switching contacts, subject to becoming intermittent when the slightest bit of dust or oxidation collects on the contact points.
@@stuartukguitarampguy5830, adding star washers to the jacks would also have been a good idea, *if* the threaded portion of the Jack was long enough that you could still tighten a nut into it with the thickness of the star washer added. If that wouldn't work, then adding a dab of some kind of adhesive, Loctite, or other compound such as Glyptol where the jack contacts the inside of the chassis would be a good idea, to prevent the jacks from spinning when the nut loosens. Otherwise, although this is only practical during manufacture, smart- money orients the jacks so that the switched contacts are facing upwards where you can see them, and reach them with a contact burnishing strip or shaped pencil eraser for cleaning. This does make the interconnecting wiring more complex unfortunately. I admit I am quite surprised that those jacks weren't factory mounted to a small strip of printed-circuit board. Perhaps they once were, but a previous tech removed the board and hardwired the jacks?
@@Sparky68M, the purpose of the star washer wouldn't be for grounding the jack, it'd be to help prevent them from spinning until such point as they got really really loose. The flat surface where the threads end is smooth and slippery, therefore minimal friction to the chassis. Otherwise, as I had mentioned, perhaps some kind of adhesive or locking compound is called for, to prevent the jacks from spinning.
Good video, Stuart. Will help those of us with old and knackered Carlsbro TCR 60's.
Very nice troubleshooting Stuart.
Cheers Monty!
Great one Young Stuart!
Thanks for sharing!
Thanks for watching!!
The audio is lifted ten Ohms above ground to stop earth loops 😉
Ah, interesting, thanks!
@@stuartukguitarampguy5830 Marshall have been doing that to their DI outputs since the seventies Stuart. Seems to work well too 😁
Nice video my friend.
@@DrWatts-bi1jv , you'll find 10 ohm ground-lift resistors in some solid-state hifi power amps as well, Adcom amps in particular. If the system has a ground loop in combination with the other components, the 10 ohm resistors will (maybe, hopefully) burn open in order to save you from burning foil traces on the circuit board. Whenever I worked on one of those amplifiers, the ground lift resistors, and the bleed resisters across the main filter caps, are the 1st things I would check. (Those amps are also infamous for horrid capacitor leakage that looks like tobacco juice, smells like dead fish, corrodes component leads and solder joints, and makes the PC board conductive; fixing that mess is a big job!).
Some pro-sound power amplifiers ---- UREI comes to mind ---- had a set of screw terminals on the rear panel where you could remove a jumper in order to separate the audio ground from the always-earth-grounded chassis, or install a resistor between them, to cure ground loops.
Excellent video... I have to replace one of the effects loop jacks on my 25555 as I'm getting a intermittent power drop from time to time.. how do I know which one to replace if I do not have testing equipment like yours?
First make absolutely sure it's the jacks by linking them together with a short patch lead. If you get the problem in that configuration it's not the jacks. If you're 100% sure it's the jacks, just replace both.
Great as always! "Someone with little knowledge..." Here in the States we'd just call the guy a jackass. 😊
Well I guess we all start out wuth a little knowledge. I'm still making mistakes!
What is the bare wire you are working with on the jacks. What gauge and where do you get it?
It's called Tinner Copper Wire or TC wire and comes in various guages called swg - standard wire guage. I use 16swg and 20swg. Of course, if you have any gash cable with solid copper cores of about the right diameter you can just strip it back and use that..
Hi Stewart, my V2b is also
114 volts and V2a is 240 volts. Is it suppose to be like that? Thanks, Nick
Hui Nick TBH I can't remember as it has been quite a while since I made this video. All the best Stuart
Why wasn't that loose grourd connection fixed when you had the jack/switch out of the way?
Hi Rich. Sory but I have no idea. The repair was done quite some months ago and I can;t remember what I did yesterday, let alone ,months ago!
At ~8mins into the vid you tried putting signal direct into FX return - no volume, and tons of hum... a trick missed at that point?
Yes definitely, but you'll note I was scratching my head about exactly that throughout the rest of the vid. ANd it COULD have been something to do with the V2b stage.
The suspect jack is clearly different than the others. Notice the difference in the molding of that jack? It's pointed while the others are flat.
Yep I reckon someone had already been in there and 'had a go'. Sigh...
At 26:30, that "sprung" leaf switch, not making contact, could be from somebody with poor soldering skills; too much heat applied for too long to the terminal, while pushing down on it with the soldering-iron tip, likely softened the plastic housing, allowing the contact to push down and away from its normally-closed, at-rest, position ---- and when the plastic cooled and hardened, the contact remained in a misaligned position. (The jack was probably bolted to the chassis first before soldering, which would help explain the erstwhile "technician" failing to see not only the permanently-open switching contacts but also that he didn't properly solder one wire).
I've seen a somewhat similar thing happen when inserting this type of jack into a PC board with really tight, too small holes, pushing the terminals up and away from their normal, at rest position, causing poor tensioning of the switching contacts, subject to becoming intermittent when the slightest bit of dust or oxidation collects on the contact points.
Yes I like your thinking on that. I was a bit puzzled about why it had sprung like that. Good thinking.
@@stuartukguitarampguy5830, adding star washers to the jacks would also have been a good idea, *if* the threaded portion of the Jack was long enough that you could still tighten a nut into it with the thickness of the star washer added. If that wouldn't work, then adding a dab of some kind of adhesive, Loctite, or other compound such as Glyptol where the jack contacts the inside of the chassis would be a good idea, to prevent the jacks from spinning when the nut loosens.
Otherwise, although this is only practical during manufacture, smart- money orients the jacks so that the switched contacts are facing upwards where you can see them, and reach them with a contact burnishing strip or shaped pencil eraser for cleaning. This does make the interconnecting wiring more complex unfortunately. I admit I am quite surprised that those jacks weren't factory mounted to a small strip of printed-circuit board. Perhaps they once were, but a previous tech removed the board and hardwired the jacks?
@@goodun2974 I think that you will find that the thread and nut of those jacks are plastic so a star washer will be of no effect !
@@Sparky68M, the purpose of the star washer wouldn't be for grounding the jack, it'd be to help prevent them from spinning until such point as they got really really loose. The flat surface where the threads end is smooth and slippery, therefore minimal friction to the chassis. Otherwise, as I had mentioned, perhaps some kind of adhesive or locking compound is called for, to prevent the jacks from spinning.
Someone with little knowledge ?? Here in Holland we call that ................our government.
Ha ha!
Sounds like a resister is faulty. If only 103 volts. 🎸🎛🔈
El-34 tubes is a good choice. 🎸🎛🔈👌