Repair Blog 003: Peavey JSX Repair, Troubleshooting, Bias Adjustmen and Review
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- Опубліковано 25 кві 2020
- I had another Peavey come across the workbench that was having trouble with volume loss and red plating tubes. I made sure to eliminate possible causes of failure before installing new tubes and powering the unit on.
I also go through the steps on adjusting the bias on the tubes and round of the video with a quick audio review of the amplifier. - Навчання та стиль
Love that you show us what it sounds like through the V30s as well as the 75s. The 75s are definitely underrated in my opinion and nobody on youtube ever demos with them!
Your content is top notch. Sub'd. After many years of avoiding it, I'm finally delving into servicing my own amps due to the lack of quality techs in my area. It's baby steps for me at this point such as cap replacement, re-biasing, and smaller issues. Your walk-thru approach is worth its weight in gold. Many Thanks!
Came to learn about how you repaired the JSX, learned that the 75's sound better than my vintage 30s i play my jsx thru. Looks like I'm gonna do some speaker swapping!!
Nice job on the amp. Some cool playing too, and a good demo of the EQ
Posting just to say I was in the first 500 subs. Your channel is the shit dude. Can't wait to see this take off.
This is the first time I have ever heard a good A/B between those speakers on a video that I understand. I am starting to dig the Peavey lineup of amps....
Great video, learned a lot. Speaker comparison was cool, and the JSX looks great without the chrome panels.
Dang man i have been looking for a video like this for a while, on where to get parts for one, and what to expect at times if looking at an amp. thanks for this, hey may have a few other questions for you as well.
The one stop shop for all the information I could ever need about my amps. Holy shit, man, you took the time to explain, suggest, indicate, and clarify all aspects of the repair, the testing, and even indicating the equipment you were using while testing. You inadvertently helped me to find my favorite speakers to combine with my Triple XXX Ultra head. Doesn't hurt that you include all the "fucks" and "shits" so I know I'm not the only one who gets frustrated while tinkering. As an aside: You're a braver man than I, blind adjusting a bias knob located so close to active vacuum tubes. Did it once when I was 5. That lesson stuck with me.
What speakers did you go with? I've got a JSX head with a Carvin Legacy 412 and Triple x 412
@theophany1770 I replaced 2 of the Sheffield 1290's with 2 B-52 A-1216's in an X-pattern. The low resonance of the B-52's sort of compensates for the really harsh Highs of the Sheffields. Idk if that would even be necessary for a JSX, as I've heard that those are a little less bright (or that they can be adjusted in such a way). I'd LOVE to nab myself a Carvin V3M with a good 2x cabinet to go with it, but I have to sell a few amps first
"It's a knob puller." Giggity!
Love that you riffed I'll Be Your Monster by Gwar. Definitely through me for a loop there
OH FUCK I JUST REALIZED YOU'RE Pustulus Maximus's SLAVE!!!!!
No, that dude is pustulas.maximus!
The biasing was a good watch, which is what I primarily was interested & assuming the rest of the amp is in good shape. That knob does the fine tuning, the test probe jacks on the back are for the multi-meter per the video as a convenient & safer probe technique. I don't think the knob is out of a range that the tubes aren't designed to bias at though. Even set at higher, level, the tubes run hotter and won't last as long as they would dialed back. With anything that is overclocked, there's more electricity & heat. Looks like you could set the knob at the test probes to somewhere between 44.5 volts and be fine with it.
nice job, talented skills! For the JSX 120 watt amp, could you tell me where the schematic is available to be able to download? Thanks!
Great video and speaker comparison. The eq sweep comparison is very good. May I ask you a couple of questions? First. What are you powering your Hella rig with? What is that you are running your AC into (brand/model). It’s a nice clean setup. Also. Can you talk more about the EQ being limited in usefulness at extreme settings? For instance I understand V3 drives the EQ. Do you think audiophile grade tubes would effect the tone sweep? I just got one of these JSX heads. I’m a vintage Marshall and fender guy playing 6v6s and EL34s so with this amp I am in new territory. This being a high gain amp do you think investing in audiophile grade or NOS tubes would make much of a difference? Like, regarding the level of rate diminishing returns, where is the current off on tubing these amps. Also, for the PI and V3 tubes... do you need a musical sounding tube in these positions or do you just want a hi quality balanced tube? Like to what extend do these positions effect the tone? Thanks, man.
Correction: current = cut off
Dude thanks for keeping in the anger and swearing. Keeps it honest and adds a bit of humour. Lol i know how it is working on shit so i love to hear other people rage too. Thanks for the great content and info!
Those peavey amps look like a service nightmare, good for us amp techs but I’d never use one myself. Nice video though dude
Damn, the G12T-75 sounds killer!
The 75 and the 70 is my favorite on the jsx for metal. They sound about the same. The speakers get a lot of hate ! Like the metal zone of speakers. probably because they came stock in some jcm 800 and laney back in the day. Idk..
I'm having tons of squealing/noise from my JSX, mainly on Ultra channel but also on Crunch. Not so much on clean. I bought all new EL34 and 12AX7 tubes and hoping that fixes it but if it doesn't, what else should I be checking? Thanks!!
diggin the videos man. Thanks! in this one you refer to "a component" that could cause red plating but I dont think you said what the component was. Could you clarify? Thanks!
Any part of the bias supply circuit that is connected to ground is very important. If any of those connections are intermittent or bad than the bias becomes unstable and red plates the tube. If I have an amp that's red plating this is where I check first, making sure all the right grounds are good then make sure the resistor values are within spec and the caps are working correctly. In some cases a component value can drift when heated. There's not always an easy answer sometimes it can take a bit of troubleshooting.
Literally just learned el presidente haha love it
That amp is a monster.
Lol.....the bass active control vibrated the camera
Actibe Eq like the triple XxX very sensitive to the slightest changes!
My old jcm900 cab has the made in England g12t75 speakers and my god it sounds crushing
Yes! Accept riff 🤘
It's well known in the JSX community that the external bias test points are notoriously inaccurate. Which I'm sure you noticed when checking the values. Great video.
Hey Man, I'm trying to find the channel Toggle switch and can't seem to find it anywhere. it's the one on the head switching from Clean, Crunch, and Ultra. Part# 71322475. do you have any Idea where I could find it?
thanks!
I have one of these amps and it has sound but can barely hear it until the volume is all the way up.
ribbon cables arent made for 7 amps of current folks. i'd replace them with 20ga
18:56 hearing this sound like my JSX cab are more Vintage30 sounding than G12T-75
Hello there Purgasound, just recently i was playing on my JSX and all of a sudden the volume dropped drastically, i can still get sound but i have to crank the volumes up a lot and it gets distorted, do you have an idea what it could be?
Check your effects loop settings and then your tubes. Replace your PI tube. Also, these amps have active EQs on the crunch/ultra channels. Turning them down can have an effect on volume. Make sure you are running at the correct impedance. Probably a tube issue. Note the effects loop volume settings and the EQ being active too though. Good luck.
@@JasonSmith-mf7xg hi Jason, thank you for your help, i will try all that
I have a question just bought a jsx use it 3 time.the owner said he had it cleaned and change the tubes.i light it up every thing lites up footswitch workes but there is no sound. What would be the problème
Check the fuses first. There might not be a HT fuse on the rear panel. It may have to be opened up. Could also be a bad speaker cable. Are the tubes glowing? If not it could be the filament supply wires on the ribbon cable have overheated and damaged their connection on the PCB.
Sorry for bother you!I have a Butcher but sounds is clean only,no distortion.This is correct?Thank you a lot
Sounds like something is reducing the volume before the guitar signal hits the first gain stage. Make sure the cables are good and the input jack is clean. I have seen the jacks need repairing on these. It may be broken at the solder joints.
If you have spare preamp tubes try swapping those first but my gut tells me it's the jack.
@@purgasound No sir..jack is fine..Sound very loud but only clean like fender twin
Unrelated but I was wondering if that JSX or anyone else's JSX makes any hum or buzz when the loop is engaged? I have tested it with nothing plugged into the loop and there is a bit of noise that is most apparent when the master vol is high but is there at any volume. I can really notice it when I use a noise gate to remove typical noise and hum which leaves only the added loop noise and maybe some normal transformer hum. I am just wondering if its normal or if the loop is just picking up noise in a way that can be fixed? Otherwise the amp has new caps and looks really clean inside and sounds great overall.
Sin Circus hey man. I've been reading that a bunch of the peaveys 5150,6505, jsx have issues with noise related to the loop. Some remedies that has worked for people: deoxidize the send/return jacks, then if there's a ribbon cable they are pulling them off and cleaning the contacts of each (deox) and they're removing the issues. I just did it with my 6505+ that I just bought used and refurb'd. Will test tomorrow and see if the problems have been solved. The loop was one of them.
@@freaksarise The deoxit the jacks thing has been done for sure. I did that the right way with the chassis out so I could see exactly where the deoxit was going and I could scrub all the metal with it. Now it could be the ribbon for sure but it's def not the simple dirty jacks or pedals making noise etc . I have tried the loop with no cables, and with 1 cable from return to send etc etc and I also unplugged the guitar cable and footswitch cable. It is def an internal thing. Maybe bad grounding somewhere, cracked solder or wiring / magnetic noise getting picked up ,or a noisy resistor etc. I'll have my tech check the ribbon ,the loop components and potential noise introducers soon. Damn virus distancing has kept me from taking it to a tech but I will soon enough. Your thoughts are much appreciated !!!
Sin Circus Good luck man. Feel free to keep us posted in this thread if you'd like. Would be cool to know what you discover. It is tube buffered? If so you probably went down that avenue already. People often say not to use EHX tubes for cathode followers, perhaps check that too? I need to investigate the statement. Maybe follow the path through that buffer across any ribbons through the loop and back. You've probably done this as well though.
Hard to say. I don't have the schems in front of me at the moment or the amp but always try the simplest things first. If the loop send or return level control is above unity gain it's going to amplify any noise significantly. FX loops usually consist of some buffers, one to reduce signal size to prevent overdriving the effect units that are expecting a guitar level signal and then another buffer to amplify the signal back to the level it was before it left out of the SEND jack. There can be a lot going on there.
@@freaksarise I forget if it's tube buffered or not. I did check all tube slots though and put in some really quiet nos and new tubes just to find out if any preamp tube or power amp tube caused noise. No help. I feel like the loop noise is an amplifying of the normal amp hum almost but with overtones that make it a bit more of a minor buzz. It's not God awful but would be a pain if recording a clean chorus part for example. It's obviously more evident on a gain channel though. Not too noticeable below master volume of 4 or so but I'm sure my ears aren't 100% after years of blasting out lol
I guess one could just use a normal pot as opposed to a “spider pot” by just attaching it to the chassis and then running wires to the proper traces. Somehow dealing with the spider pot just seems like a pain in the ass to me.
Change your tubes before they fail. Look at them every once in a while while the amp is on and being played. If they're red plating take the amp to a tech.
Are these good amps?....I have a chance to get one under 500$...it has 6l6 tubes
They're not bad. The tone is pretty good but I think the flexibility is limited by the way they designed the EQ controls. They have a large range but they boost and cuts are really extreme. As far as reliability goes it would probably need work on that ribbon cable at some point after some years of the heater wires overheating.
Hey man, thanks for the advice. I passed on the deal...im trying to get a 1989 jcm 800 from a friend who doesn't wanna part the head from the cab!...
g12t-75 sounds much better than the v30 to me
Where is your shop
An hour west of Richmond, VA
Both speakers at once would sound cool mixed together
Amp sounds great, actually. I think people are turned off by the terrible looks.
Those JJ tubes are junk