E06 - Marshall JTM45 Clone - Analyze, Repair, Bias, and Test
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- Опубликовано: 7 авг 2024
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This 1989 Marshall JTM45 Reissue/ Metro point-to-point upgrade came in with a broken input jack, and a broken tube socket. As usual, we had some unpleasant surprises after we fixed the obvious problems. We diagnosed a red-plating tube and show a few measurements that are helpful for setting output tube bias. After the repairs, this amp sounds fantastic for country/blues crunch or early creamy power chords.
00:00 - Opening and description
01:37 - Teardown and Inspection
03:04 - Tube socket repair
07:12 - Input jack repair
07:43 - What's a cathode-follower driven tone stack?
10:10 - What does a red-plating tube look and sound like?
11:08 - Tim calls!
12:44 - Verifying the output tube connections
16:06 - Checking output section "hot"
20:17 - Biasing (with some of my personal biases revealed!) - testing and verifying.
26:14 - Testing
Wow! I just noticed that lovely Dirty Blonde Ale by the 'scope! I wish I had another one left!
Love the videos - excited for more! Informative, clearly explained, & your occasional mentions of the business side are something pretty unique (and welcome) when it comes to tech tutorial/repair videos. How it's done in the real world, when you have to both deliver solid repairs for someone else and still get some compensation for your work. Great stuff.
Awesome, thank you!
Instablaster...
That’s a lot of work. Enjoy watching you do it from here in Portland Oregon 🎈
Thank you for the time put into the videos. They've been informative and entertaining. Looking forward to new videos. Thanks again!
I always install a 1 ohm resistor at conn'n 1and 8 to ground. Thus you can measure the mV and get the actual current drawn to set the proper bias using Ohms law
I hate it when something moves while working on it, device starts working as it should, but gives me hard time to find actual fault like solder joint. I tend to resolder good components on moving tube sockets because it often takes less time than searching for not obvious problem. Of course that's just my approach. Nice video and repair here mr. Wally.
There you are!
i like the shunt method for biasing
Regarding the comments on biasing with a 1 ohm shunt resistor. Sure, go ahead and install them in your amp. When you work on other people’s amps, if they didn’t ask for it, *DON’T* do it. Measuring the actual current and voltage of the power tubes is just faster and safe if you know what you’re doing.
thank you very instructive :o)
Thanx for video.
KT-66’s are the original tube types on this amp; how do they compare sound wise to the 6L6’s?
Very nice video; thanks for sharing.
What brand is that clone?
i try to understand how does it work (amp i mean) and try to build one myself
Love this video!
I have question though. I'm probably dumb for asking this but here goes: when you first pulled the amp apart, I saw your fingers close to the innards of the amps. I'd be too scared to do to an amp I'd just opened, in close the caps were live. And later at about 12:30 or so, you drain the caps and then remove the alligator clips from the chassis. I was told it's best to leave them on in case the caps recharge, which I've seen happen on my build despite it not being connected to the mains.
I'm sorry for asking, I'm a complete hack job, I'm honestly just trying to understand things before I build my second amp (a 5e3 clone...which tells you have new I am to this)...and live caps scare the living day lights out of me :-)
Yeh and don’t poke around in an amp like this with a screw driver. I don’t care if you’re certain the caps are drained. IMO it’s not very bright and sets a bad example for someone that’s learning
Sorry, I've been gone a long time. I ALWAYS check the B+ before I work inside the amps. If the caps "recharge," it's only to a few volts. Often in these videos, there is a lot of time between "shots," and I forget to mention that the power has been down for a long time. BOTTOM LINE: ALWAYS check the HV (B+) circuits with a tested DMM before continuing work. Have fun!
Your opinion, your work methods... It's science, not magic. If it's dead, it's dead.
Is that a Big Apple Strat?
Ótimo
Sorry mate but a bit disappointed with the way the amp was bounced around and plyers on nuts, sloppy work methods. Always a good idea to know the amp you are working on and thoroughly inspect an amp before working on it, saves all the silly apologies.
But you got there in the end.