apdale Posted July 11, 2008 Share Posted July 11, 2008 First off I've got a Ver3 Epi Valve Jr. that no longer produces sound. So, I had previously completed several modification to my Valve Jr. including adjusting the plate voltage down to 300V. At the time it quit working I changed out C5. Then when I put everything back together there was no sound output. I opened it up to check it out and I now have a plate voltage close to 400V, but it seems to disappear if I turn the volume up past halfway and never comes back. I looked at the input to the EL84 at pin2 and it appears that my waveform is over 100V peak-to-peak (measured with an oscilloscope) when the volume knob is pointed at 12 o' clock. I have no idea what could be wrong, I have changed C5 back to the original part and reflowed all of my solder joints. Everything appears to be grounded and attached, verified with my multi-meter. If anyone has any ideas on what could be wrong please let me know. Link to comment Share on other sites More sharing options...
Just Strum Posted July 11, 2008 Share Posted July 11, 2008 I can't help you, but I can direct you to the guy I purchased my mod VJr from and he might be able to help. Here is his site and there is a way to contact him on this page. If no one here can help, contact Bob (duhvoodooman) and he will help or point you in the right direction. http://duhvoodooman.com/ Oh, welcome to this site. I just joined and it seems like a good site. Link to comment Share on other sites More sharing options...
apdale Posted July 11, 2008 Author Share Posted July 11, 2008 Also, I forgot to mention that I changed out the EL84, no change. Could the 12AX7 be the problem? Link to comment Share on other sites More sharing options...
Steven Lister Posted July 11, 2008 Share Posted July 11, 2008 BROKE IT?!? That's it man, you're out of the club! Just kidding. Really, WELCOME to the forum apdale! I'm not a modder -- only an avid V3 player -- so I won't even effort to muck things up for you. But never fear. The tried, true and tested mod experts (E_T, M-Theory, Layboomo, CGil & company) will be along shortly to walk you through the shake-out. The VJr. is pretty simple so expect the best and I hope you're back on-line pronto. Hit every BLUE NOTE baaaby..., I'm going to play on:-" Link to comment Share on other sites More sharing options...
TWANG Posted July 12, 2008 Share Posted July 12, 2008 take your question over to sewatt.com .. the first thing they'll say is recheck all your work... make sure it's not just a solder joint that needs reflowed.. and make sure everything is in right.. that's usually the problem! but they'll be able to diagnose beyond that, too.. Link to comment Share on other sites More sharing options...
layboomo Posted July 12, 2008 Share Posted July 12, 2008 Double check your values and connections on r-10 and r-14....and r-12 while your at it. I doubt the 12ax7 is the problem...and you've ruled out the el-84 already. If that doesn't help go to sewatt and post your voltages and describe the problem and I'm sure someone there will guide you. Best of luck! Quick question.....your heaters are fine.....ie tubes light up yes? Link to comment Share on other sites More sharing options...
apdale Posted July 12, 2008 Author Share Posted July 12, 2008 Yes, the heaters are fine the tubes are lighting up and I measured 6.3V across pins 4 and 5. Double and triple checked all my solder joints but I'll go over them again just to make sure. Link to comment Share on other sites More sharing options...
cGil Posted July 12, 2008 Share Posted July 12, 2008 Sounds like you have a problem with your cathode circuit. Since you're playing with silly scopes and meters, I'll have to assume you've got the polarity of C5 correct. For the newbies following this thread, I should mention anyway that "+" end of the cathode bypass cap always connects to the cathode, and the "-" to ground. Anyway, make sure you're actually getting continuity between C5, R14, and pin 3 on the tube socket. Might simply be a broken trace next to a solder pad causing your plate voltage to jump like that. Gil... Link to comment Share on other sites More sharing options...
apdale Posted July 12, 2008 Author Share Posted July 12, 2008 Definitely have continuity there, thats one place I checked and rechecked since thats where it seems the problem should have to be. I definitely have the polarity right also, I even tried changing to another cap and I've got the same result. I also forgot to mention that I did have a signal output at the output connectors but it was only the top half of the wave; since it wasn't sinusoidal I'm not hearing anything. I probably should have remembered everything I've now added in...maybe that would have helped fix this sooner... Thanks everybody for the help so far, I'm confident it'll soon be fixed. Link to comment Share on other sites More sharing options...
Eracer_Team Posted July 12, 2008 Share Posted July 12, 2008 NOTE: Power on trouble shooting information… please follow precautions otherwise your life may end quicker than you think… Watch out for the el84 socket, you may have opened up one of the tube socket pin holes; might want to look at the socket with the tube out. Tubes light, so that busts the heater thing... notice we all asked what the voltages are at.. Print off the schematic (probably done already) and chart down the voltages across the power supply r10/12/13. Then the voltages on the two tubes; black DMM lead on the star ground and the red lead can probe pin 1,3,6,8 of the input tube and pin 7,3,9 of the el84.. Remember to hook up your speaker when testing with live voltages. Look carefully at the R6/R7 area, this is a place that many make mod's to but it is also the place where the signal is passed to the volume pot. Also when probing with the DMM connect the black lead to the star ground, then take your red lead and with the volume at zero, touch the red probe to pin6 of the 12ax7 input tube, you should hear a pop sound on the speaker. Care must be taken with live voltages and the covers off Link to comment Share on other sites More sharing options...
apdale Posted July 12, 2008 Author Share Posted July 12, 2008 I'll check that out monday, my amp is currently at work (thats where I have access to the scope.) That is something I haven't checked tremendously but could be a definite source of the problem. I'll let you know after I check it out. Link to comment Share on other sites More sharing options...
Eracer_Team Posted July 12, 2008 Share Posted July 12, 2008 are we talking about the stock volume control too? did you reconnect it... yes I know what it sounds like but all of us have done that at some point in time. and the stock input connect is a jack to the pcb as well. Link to comment Share on other sites More sharing options...
apdale Posted July 12, 2008 Author Share Posted July 12, 2008 Yes its the stock volume control and yes its connected. Sometimes its the easy things that are the hardest to figure out.... Link to comment Share on other sites More sharing options...
apdale Posted July 14, 2008 Author Share Posted July 14, 2008 Eracer_Team Here are the values you wanted. Hope this gives you a better idea of whats wrong. Thanks for the help. r10- 6.3V r12- 13.5V r13- 28.6V 12ax7 1 -192 3 -1.2 6 -189 **NO POP* 8 -1.2V el84 3 -0 4 -65mV 5 -6.9V 7 -375 9-362 No pop on speaker when pin 6 is touched with DMM, not sure what that means but hopefully it helps. Link to comment Share on other sites More sharing options...
cGil Posted July 14, 2008 Share Posted July 14, 2008 Those voltages are too wacky to be real. What's up with your meter? Check the battery or voltage type selection. And are you certain you hooked the orange wires and red wires back to the board correctly? There are some annotated pics of the board over in the SEwatt FAQ, in case that'll help. http://www.sewatt.com/node/16287 Gil... Link to comment Share on other sites More sharing options...
apdale Posted July 15, 2008 Author Share Posted July 15, 2008 I checked it with two different meters and double checked all my wire connections.... Link to comment Share on other sites More sharing options...
cGil Posted July 15, 2008 Share Posted July 15, 2008 Looks like it'd be a good idea to scrutinize everything under a magnifying glass. Go back over that amp, one connection at a time compared against a schematic. Cross off absolutely every wire or trace, every connection, and every part on the schematic as you confirm it on the board. Somewhere in there is a problem that's making your voltages go out of whack, so don't trust anything you've done. It's usually whatever you're sure you did "most right" that winds up being most wrong. So park the ego, dive back in, and conquer that thing. Gil... Link to comment Share on other sites More sharing options...
Eracer_Team Posted July 16, 2008 Share Posted July 16, 2008 I concur with Gil. R10 is at the front of the power supply and to have 6.3v is what I think are heater voltages, its interesting that R12 and R13 increase voltage where they should be dropping in voltage. Just a guess: I think you swapped the orange and red wires from the power transformer to the board; which causes other issues as well. also R10 gets its power from the diode bridge which gets its power from the PT. Check your diodes 4*1n4007. If you have to replace them put in the UF4007 diodes. Link to comment Share on other sites More sharing options...
layboomo Posted July 16, 2008 Share Posted July 16, 2008 I concur with Gil. R10 is at the front of the power supply and to have 6.3v is what I think are heater voltages' date=' its interesting that R12 and R13 increase voltage where they should be dropping in voltage. Just a guess: I think you swapped the orange and red wires from the power transformer to the board; which causes other issues as well. also R10 gets its power from the diode bridge which gets its power from the PT. Check your diodes 4*1n4007. If you have to replace them put in the UF4007 diodes.[/quote'] Yeah but he said he's got 6.3v on pins 4 & 5........Hmmmm? Link to comment Share on other sites More sharing options...
apdale Posted July 16, 2008 Author Share Posted July 16, 2008 I've got 6.9V on pin 5 and almost nothing on pin 4. Is that correct? Link to comment Share on other sites More sharing options...
cGil Posted July 16, 2008 Share Posted July 16, 2008 I've got 6.9V on pin 5 and almost nothing on pin 4. Is that correct? Yep. That measurement's correct. A little high, given the 10% leeway on 6.3v heater filaments, but it's essentially correct. It's a DC heater, so pin 4 of the el84 will be connected to ground. Gil... Link to comment Share on other sites More sharing options...
apdale Posted July 16, 2008 Author Share Posted July 16, 2008 thanks, just making sure Link to comment Share on other sites More sharing options...
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