massless wrote:Hi - I've lurked on this thread on and off and picked up some good tips. Installed depth mods on both my JCA100H and 20H. However my 100H has developed a fault and I wondered if anyone here could help?
The Normal channel has gone kaput. Happened while playing at home, it went pop and just left a loud hum instead of a signal. Odd thing is the OD channel is working perfectly. Its not a preamp valve (swapped them all) so I'm a bit stumped about what it could be. Any ideas?
EDIT: measuring a few of the resistors and R48 by the input jack is reading 0 ohms. Could that be it? (disclaimer - i'm not an electronics expert!)
Gonna start with my usual disclaimer - if you haven't discharged your filter caps (or even know what I'm talking about), you need to put that thing back together and take it to a tech. Probing around inside your amp could be lethal if you hit the wrong thing. I'm not kidding. We don't wanna have to tell your next of kin that you're having to get your feedings intravenously (if you're lucky) because you were trying to save a few bucks.
I'm going off my 50H schematic, but I'm pretty sure values & identifiers are same with the 100H - at least for the preamp section
If the OD channel doesn't sound any different, I wouldn't think it'd be R48 (1Meg - Brn/Blk/Blk/Yel) as that appears to be tied to the main input and would affect both channels. It may be reading zero resistance now because it's in-circuit. If you pull the V1 tube, does it still read zero?
I'd start with the easy stuff - did you carefully check your wiring for the depth mod? Is there any chance it's shorting something out? Did you do any other mods, like the T-Filter or clean / scoop switch?
You might check out:
R42 (also 1Meg) or C28 (270pf)
C29 (0.022uf), C23 (120pf), or R34 (2.2Meg)
The normal channel gain pot (VR9)
The normal channel volume pot (VR4)
The relays used for switching channels: VT4A and VT1A.
I could be wrong, but that appears to be the only components unique to the normal channel
Thanks for the reply Grimespace. You're right its not R48 (I removed one end and the two pads were still showing 0 ohms and giving me a continuity beep. I have a feeling its a dry joint somewhere because after fiddling with it and retesting the normal channel was working fine. THEN the OD channel dropped in volume and became thin. Switched off, rebooted, and all was fine again.
Will go over the preamp socket joints and resolder them, see if that works, as they look the worst. If its still playing up I will check your component suggestions.
Been a while, guys. Looks like you kids have been trucking along. Still hoping to pick up a 50H at some point to play with some more, but I AM about to do a Britification of a 100H.
I'll peep back in here from time to time and get to some of the fun stuff here.
And Marshallnoise, I'll look into the lower gain for the Browneye. It might be kind of hard to do a "simple" gain reduction based on how the circuit is changed. Essentially, the first stage runs wide open into the second and drives the hell out of it. So, the easiest way to reduce the gain might be to bypass a gain stage completely.
GRIMESPACE wrote:Glad to hear you were able to work it out. What 6L6s are you running?
I have talked on and off with Jay about doing a couple of mods to enable running EL34s. Everything from SGRs to transformer changes was considered. I posted a vid some time ago where Mike Soldano changed a 50H over to EL34s (I think) with a few component changes - no transformer - so it might be pretty straightfoward. At some point, I'd like to give it a shot. I'll tell you what, though - the slope resistor / voicing mod we did back on the first couple of pages made a huge difference in sweetening the overall tone for me.
The only things you must change for EL34 operation are: 1. Screen grid resistors 2. Adjust bias properly for EL34
Screen grid resistors should be 1k ohm 5 watt. some pics farther back. If you decide to go back to 6L6s just rebias, no need to swap the SGR back
I have an issue with my JCA22H and I have no idea what it can be. I am almost positive it is passed the warranty period so I may be boned in that aspect...Anyway, the first one I ordered was doing this right out of the box. I would power it on, wait a good minute and then flip the stand by switch. Nothing. I'd slowly turn the volume up, and it didn't matter which channel, but the thing wouldn't make a peep until I hit between 3 and 4 on the volume. It might work every 10 or 15th try, but not always - sometimes it would never work right.
I sent that back and got another which had been working fine for over a year now. Was playing fine yesterday...Turned it on today and it is doing this same shit. Nothing as far as output until I hit 3 or 4 on the master and even then it is hissing and muddy and all around shitty - cutting in and out. I have already tried swapping tubes. I had a few of the original Chinese jobbers I pulled out that I tested in another amp, so I know they work, and still nothing. I have swapped all 5 preamp tubes and both power tubes and still no joy. It doesn't matter what channel it is...If I have to try and get a video of this thing doing it I will try. I was just throwing this out there on the off chance that someone may have had a similar experience or the same issue all together. Any help would be appreciated. Thanks.
Guitars: Early 90's Ibanez EX Series, Late 80's B.C. Rich Mockingbird, Fairly new Epiphone LP Custom Amp: JCA22H with 4x12 Ibanez Cab No pedals or any real skills...
I would open the amp and look, if all cables are connected to the power and standby switches. They are not soldered, just plugged over the lugs with sockets, sometimes they fall off.
But take care of the high voltage. Switch the amp off, plug off the power cable and wait a few minutes, then check with a dmm, if there's any voltage left. Shouldn't be anywhere over 5V if the amp is ok. But if it's really damaged, there cut be higher voltage.
Thanks for the reply. Gonna pull it apart once I get the chance and see if there is anything out of the ordinary going on in there. I have been searching for answers and it seems that the bias pots are where the problem is - either a bad pot or a crap solder joint. That's what I'm hoping for actually - shouldn't be too hard to fix if that is the problem. Hopefully I can get this fixed without having to spend any money on it. We'll see what happens...
Guitars: Early 90's Ibanez EX Series, Late 80's B.C. Rich Mockingbird, Fairly new Epiphone LP Custom Amp: JCA22H with 4x12 Ibanez Cab No pedals or any real skills...
Finally.....found an answer to my FX loop problem in the JCA5012c, I put this mixer in line first, insert out to mixer with the mix level halfway. It works, no more crackle in the notes I'm using with a zoom g1on. It also works as an attenuater, now I can turn the power amp up, everything just sounds so much better. The funny thing is I've had this for years and never really used it on anything, I have other mixers and tried them the same way and they didn't do what this thing is doing, it's not coloring my tone. I'm not sure if it's just acting like a volume pedal
Quite impressed with you US types ;-) ordered a bias adapter on eBay (the one that sits under the tube) and it arrived 3 days early! After some fun and games removing the back baffle - tolex sweat stick - I (or more rather my wife, aka my in house tech) have successfully biased my first amp! I will buy some new valves soon - just wanted to see what difference re-biasing did when i could do a stock a-b comparison - and wow it has really opened up the amp, almost a completely new amp - loads more sustain and it sounds definitely more gainy.... was biased at factory at 9.7ma - now running at 36.0ma ;-)
GRIMESPACE wrote:Hi - welcome to the group. I forgot about the back panel - yep, it seems that they tend to stick together, as you've found. Just gotta dig in and pull. As long as the screws are out, it should release cleanly.
Yep - mine made an awful sound but turned out to be the tolex squeaking!
GRIMESPACE wrote:Hi - welcome to the group. I forgot about the back panel - yep, it seems that they tend to stick together, as you've found. Just gotta dig in and pull. As long as the screws are out, it should release cleanly.
Yep - mine made an awful sound but turned out to be the tolex squeaking!
Glad it worked out for you. Honestly, I leave mine off for the most part (hasn't been out of my studio yet), and I made a custom front panel (framed expanded metal) with velcro so I can change tubes real easy.
GRIMESPACE wrote:Hi - welcome to the group. I forgot about the back panel - yep, it seems that they tend to stick together, as you've found. Just gotta dig in and pull. As long as the screws are out, it should release cleanly.
Yep - mine made an awful sound but turned out to be the tolex squeaking!
Glad it worked out for you. Honestly, I leave mine off for the most part (hasn't been out of my studio yet), and I made a custom front panel (framed expanded metal) with velcro so I can change tubes real easy.
Howdy boys. I'm back in the club again (I still have the Earhart so technically never left haha).
Picked up a JCA50H on the cheap today. It does have a problem. Plugged in and played, and it seems like a bad solder joint somewhere - no bass, no mids, just all treble and a slightly lower volume. No bass adjustment will change the sound, no mid adjustment will change the sound, but I can adjust the treble and it will cut it if I turn it down. Sometimes it'll "kick in" and wallop me with full sound like I'm used to with these amps, but then it kicks back to the all treble thing. I did replace all the tubes so I doubt that is the problem. Any clues on what I should check on the PCB?
Resident thread killer
I know nothing
Sterling AX40 x3 PRS SE245, SE Paul's Jet City amps - all of them modded 2204s Bogner XTC 3534 Kemper rack
I don't have the schematic handy right now, but it sure sounds like an intermittent connection to me. There's only a few components in the tone stack, so shouldn't be too hard to isolate those parts and check them out. If I get a chance (and nobody beats me to it), I'll get a look at the diagram later today and let you know which ones the are.
I'm wondering if its relative to the input jack or not far down the line from it. I had it on for about 10 minutes just now and it kicks in and kicks out like a short in a cable would do but without the buzz. I have just enough practical experience with electronics to do the SLO mod (which I successfully did on my old JCA100H), but that was essentially with Cliff Notes and applying what I learned via YouTube vids and this thread really.
Resident thread killer
I know nothing
Sterling AX40 x3 PRS SE245, SE Paul's Jet City amps - all of them modded 2204s Bogner XTC 3534 Kemper rack
I had a bad joint n mine. The bias pot was intermittent, and would cut in and out like you described. I went over every solder joint I could get to after that. All has been good since.
I'll start by imparting my effortless polarization by virtue of participation..
New owner of a JCA22H here... the recent Stupid Deal of the Day on MF got me. So far the amp seems a bit on the harsh and bright side, so first thing is a tube swap and bias. I'll let it settle in for a month or so before I start modding, but the depth and SLO mods have peaked my interest.
Welcome to the club! Depth mod is an absolute MUST, and is actually relatively easy to do (not to mention cheap!). You'll see a broader improvement of tone with a tube swap than with the depth mod, but both are in my opinion essential to getting the most out of the Jet City amps.
Resident thread killer
I know nothing
Sterling AX40 x3 PRS SE245, SE Paul's Jet City amps - all of them modded 2204s Bogner XTC 3534 Kemper rack
