You da Man, Chris. Thank you very much for sharing your wisdom. Keep those old electronics alive; do it right; do it with integrity; attention to detail; no shortcuts!
You have just made my day! Comments like yours inspire me and my colleagues (@PsionicAudio, @BradsGuitarGarage, @UncleDoug, @HeadfirstAmps, @TheGuitologist, and many more) to continue making videos. On the other hand, Trolls make me want to turn off my video cameras permanently. There's no money in making YT videos. Its just for the love of it, and getting to "meet" people like you. Thank you.
Hi Les. Yes, it's good to be doing another video. I have been so squashed with repairs that the videos have taken a back seat until I am more caught up. Thank you for asking about my daughter. We’re all going well, thank you God! I use a chopstick to hold the wire in the solder puddle to make the best connection. Some insulation gets a bit soft when using the high-heat soldering iron. It’s a sound connection.
Hi Chris, my good man! So great to see this video! When I start working on electronic noise issues, I start with a 'ground' up.approach. In the world of audio ground noise issues, reducing and isolating the DC ground resistances are very often the root cause of the issue. Inductance is not a significant factor at audio frequencies. Your analysis and implementation in a JMP-50 is the best part of this video (for me). And yes, Jimi with a Marshall and a Stratocaster is the ultimate test for this amp! Yea, he did not play JCM 800 amps. Congratulations on this video and you guitar playing!
I bought the combo version of this amp new in 1977. I was new to the guitar and it was my first tube amp. Sadly, in 1978, I sold it to buy a solid state amp with more bells and whistles. Though I still have and use the amp I replaced it with, selling that 2104 is something I really regret. Not to mention that now it would be worth 5 times what I paid for it in 1977. Glad to see some still out there and being taken care of.
Hey Chris another detailed great video. I used to own a '77 2203 bought back new from the UK by my long suffering parents while on a holiday. Bought from Macaris London for the princely sum of around $240 AUD. Unbelievable I know but that was the price back then. Regretted selling it years later for a decent profit but really what can you do with a 100W fire breathing monster of an amp for playing around the house once your gigging days are done?
What wonderful parents! You're spot on, Robert. Where can you play 100w today? I haven't even played my 40w Brownface Concert for 17 years!! But at least we got to do it back then. I feel for the poor kids of today who will never know the feeling of being strapped to the front of a steam locomotive (aka a Superlead or a Twin on 10).
Hey Chris, great to see another one of your master tech videos..! Tips and expert info, just fab.. Nice bit of rocking out to Jimi..Take care..Ed..uk..😊
Great job my friend. I have always been able to improve the noise floor on older Marshall’s by improving the grounding in much the way you did it. Cheers.
I have a clone JMP 50 built here in NZ. Sounds great, but I am always looking for improvements or tweaks to taste. Grounding is something I'll check now. Cheers. So far all I have changed is I've split the shared V1 cathode, so it has the 0.68uF and 2.7K setup on V1b. I have also tried changing that coupling cap between the first two tubes. 0.0022uF instead of 0.022uF. I am not sure I'll keep it that way, plus I like the look of the mustard caps it came with. I've also tried various bright cap values. All pretty basic stuff. Maybe the biggest improvement was had by trying the various preamp tubes I have. Just looking for the least noisy combinations of them in all three slots. That and sourcing some tube shields for them helped with noise. I'd like to find a good 7025 tube. Supposed to be very quiet in V1 but still sound good. Once I got the preamp noise down, the presence control is less prone to oscillation when everything is turned up (still scratchy though, but that's normal for this design apparently). Power valves are Mullard reissue EL34. Seem pretty good so far. I have a pair of those old Sylvania 6CA7s like Van Halen used. Last time I checked they were barely within matched, so I do not like using them, plus I do not want to use them up for everyday use, because they are very rare now. It did not have a head cabinet. I ordered one from Ceriatone, but it does not look right. Ones that do look right from the USA tend to cost almost as much in shipping as the cabinet itself. Stuff that. Not sure what to do. Sometimes I think about converting it to 2204 spec, but then I think nah. Having a good sounding Plexi is nice to have, so why change it to something else is what I think. Then i toy with the idea of build a MKII master volume amp. A little above my pay grade yet, so i think I should build a 5F1 amp instead.
HAHAHA! You build a 5F1 after a JMP Plexi? No way. Yes its hard to find good modern production 12AX7s. I have had good luck with the TAD 7025s, but my favourite for V1 is a 5751. To my ear its a much better sounding tube than a 12AX7. Good luck with your fun amp journey!!
It's great to see you back making videos Chris. I hope you and your daughter are OK. Another great video. It looks like your soldered earth lead got squashed a bit!
Good one Chris! I heard or read somewhere that the piano wire link between the pots was mainly to stop them rotating if their mounting nuts became loose? But I'm not sure. Does that link wire separately connect to chassis earth? - I couldn't see. What wattage iron do you use to solder the earth wires to the chassis? I bought an 80W iron from ole mate Jaycar electronics, which was the highest power iron they make, hoping it would be enough. I used to have a 250W iron with a 1 inch diameter copper tip! - Which unfortunately got incinerated when a firestorm burnt my sheds down, & nearly my house along with them. Those Vishay metal films sound like a great choice mate! - As do the fnt (?) filter caps. I like your idea of grinding down a metal nail file for the phone jack contacts. We won't tell the missus! Shshh! That original V1 was definitely kangaroo Edward, as well as not knowing the words! Did I miss the the point where you said a bit of assymetry gave nicer 2nd harmonics, but then you said the 27% difference in bias was no good? I missed the nuance there! Loose bolts all over the place was a bit of a surprise, but good thing you checked em & tightened em! Maybe a bit of nail polish might help ya reckon? Nicely done overall & you should have another very happy customer! Liked the "back in black" & "baby please don't go" sound test! - Noice!
Neville mate, you have made my day. My soldering iron is a 120W Weller. Yes, a bit of asymmetry will increase 2nd order, but its almost impossible to bias 27% difference without one valve being too hot or too cold....and too much mismatch can sound shyte to me. Thanks Neville.
Another fantastic video Chris. Thanks a lot. Rookie question. Why take the grounds to two separate stars instead of just one. Would that not be even better ? Cheers
In theory, you may be right, but when you consider that the Preamp is the most sensitive section to noise, because of the lower signal levels, and the power stage is the noisiest (closer to the rectifier and much less filtering than V1). Also in a Class AB power stage you have the added benefit of common mode rejection (with the OT) that you don't have in the preamp. That was bad grammar. Sorry, but I think you understand my ramblings.
A beauty. What's your experience with those impedence switches? I've seen them for a good price but didn't know if they could handle current.. I've tried the alpha ones as well, and they worked, but then I read they also are questionable. There's a 20 dollar switch I've used as well, but I don't particularly like spending all that much if i don't have to.
Please don't skimp on Impedance switches. You don't need me to tell of the consequence of failure. I found 2 replacements in the past, neither of which fit properly without some convincing!
@theguitaramptech thanls for the reply..that's what I thought, lol. The switch in that marshall is a knockoff of a lorlin switch. A lot of the Diy Dr. z airbrake clones have them, and I've never been confident they're safe.. the alpha ones scare me too , ha. Although I've seen a fryette video where he's looking at a marahall that Dumble worked on and he used one, jumperibg each gang for more current handling. But when you look up the current rating on those, it's super low. I guess I shouldn't skimp on that particular part , as you say.
Hi Chris, great video as always. Are you really sure the JMP 2204 and early JCM 800 2204 are different. I have to look into my JCM , but I think the pcb looks almost the same. Greetings from Germany Markus
I have a question about the death cap. Can you put a 1meg ohm resister in series with the cap. Instead of removing it. Will it still do it's job filtering noise but not the shock hazard when installing a 3wire cord?
Good thought Dwight, but NO. Please don't. If the death cap shorts it will still connect Active to the chassis. This can lead to serious health issues!! If you insist on using a LINE TO GROUND capacitor, like the Death Cap, then you MUST replace it with a Class-Y safety capacitor that is designed to fail OPEN which may save your life one rainy day. (A Class X is designed to fail SHORT, while a normal Death Cap is to fail "whichever way chance takes it".)
That's a good question. I much prefer to solder my main earth points to the chassis. With an Al chassis we have no choice but to bolt, usually with a steel mounting system to Aluminium. I am suspicious of the galvanic potential that can cause corrosion/conductivity issues in an amp. I don't expect the resistance of Al vs Steel to be a significant difference. Good question. You made me think!
@@ampyamps I recorded this repair back in the Aussie summer (its mid-winter now), so I can’t recall amp specifics. However, I can tell you that earlier Marshall models did not have screen grid resistors. If this was the case here, I would have decided not to install them as changing screen grids can have an impact on the tone of the power stage. Thank you for noticing and commenting.
Oh no! Don't tell me I edited that out in my desperation to shorten the video. Yes, I changed them. If my memory serves me well, and it usually doesn't, I used TADs
interesting you grounded the middle and presence pots to the reservoir cap ground. i never tried that. What would be the difference grounding those near the pots on a ground lug to chassis? (not to drill a hole for this amp as it is vintage)
Sure you can do a separate ground; it would be better than stock. The biggest improvement is just separating the preamp and power stages. Lyle @psionicaudio has an excellent video on grounding for Marshall amps. Check it out.
