supersoldier71 Posted December 19, 2008 Share Posted December 19, 2008 My Valve Jr Combo (v3) will power up, but no sound comes out. I mean, the on/off switch lights up when you turn it on, but you get no sound. I changed the pre-amp tube, but I suspect that I may have to change the power tube. Or something. I really don't know. Any advise will be apppreciated. Link to comment Share on other sites More sharing options...
TWANG Posted December 19, 2008 Share Posted December 19, 2008 check the fuse holder.. most common problem they have.. the connectors don't connect sometimes scratch the metal fuse ends up. that helps them connect.. reinsert TWANG Link to comment Share on other sites More sharing options...
m-theory Posted December 19, 2008 Share Posted December 19, 2008 The heaters have a fuse...maybe it's that oft-mentioned Vjr issue, where the fuse loses contact. Try taking the fuse out from the orange wire in back of the PT, and sand each end a bit, to see if that restores it. I haven't personally had this problem myself, but have read about it many times. The other possibility is that the jack is spazzing out. It's a POS jack, so that's entirely possible, as far as I'm concerned. You could try unplugging and re-plugging the speaker cable. Also, might as well check the connections on your speaker, although if one of those came off, you've probably already smoked your output transformer. An output tube won't generally just quit altogether, unless it shorts out, at which point, it would take the main fuse out (hopefully) as well, but if you've got a power light on, that can't be the case. It wouldn't hurt to try a different tube, of course, but I'd look elsewhere first. Link to comment Share on other sites More sharing options...
m-theory Posted December 19, 2008 Share Posted December 19, 2008 Beat me to it, Twang! Link to comment Share on other sites More sharing options...
supersoldier71 Posted December 19, 2008 Author Share Posted December 19, 2008 Pardon my ignorance: what's a PT? Also, I don't think it's the jack because when the amp is on I get nothing...not even a buzz. Link to comment Share on other sites More sharing options...
m-theory Posted December 19, 2008 Share Posted December 19, 2008 Power Transformer. A broken output jack would give you no sound, as would the smoked output transformer that would likely result from playing the amp in that condition. Check that fuse on the orange wire first. If it's not that, check that output jack and the speaker connections at the speaker. If it's not that, it could be the output tube, and if not that, the amp will likely have to come apart. Link to comment Share on other sites More sharing options...
supersoldier71 Posted December 20, 2008 Author Share Posted December 20, 2008 If a barely literate fellow (like myself) were to accidentally plug the speaker jack into the wrong output would that kill the amp? Link to comment Share on other sites More sharing options...
m-theory Posted December 20, 2008 Share Posted December 20, 2008 Maybe. The amp doesn' t know or care whether or not you're literate. If someone drops a wrecking ball on it, it's going to get squashed flat, regardless of the IQ of the person who drops it. Impedance mismatches can absolutely kill an output transformer. Some amps can handle a 100% mismatch, others cannot. Link to comment Share on other sites More sharing options...
layboomo Posted December 20, 2008 Share Posted December 20, 2008 I always check for the "stupid stuff" first. You said that you replaced the preamp tube......it could be as simple as a bent pin on the tube which is quite easy to do actually. Next is the fuse holder thing. I don't suspect the output transformer right away from your description but they must have a load(speaker connected) at all times. If you played the amp with no load for any length of time you most likely need a new output transformer. Best of luck it's probably something "stupid"! Link to comment Share on other sites More sharing options...
TWANG Posted December 20, 2008 Share Posted December 20, 2008 the pt is the big block next to the tubes.. the ot is the smaller block next to the tube.. power transformer.. output transformer.. bent tube is a good call.. I bought two vjs from MF as seconds... neither worked until I roughed out the fuse ends.. then both were perfect. did you? I mean.. was it working.. then you replugged in the speaker.. maybe moved it and unhooked it then hooked it up? it probably would have worked a bit before frying is what I'm getting at, not just not worked at all. I still think it's a fuse.. or just something that's come loose and isn't letting a signal get through. TWANG Link to comment Share on other sites More sharing options...
strangedogs Posted December 20, 2008 Share Posted December 20, 2008 2 of my VJ's developed the "dreaded fuse connection" issue... I snipped out the stock fuse holder and wired in a RAT SHACK replacement - Voila' - Problem Solved. Very easy to change fuses too now. Link to comment Share on other sites More sharing options...
cGil Posted December 20, 2008 Share Posted December 20, 2008 If you've checked the fuses, and cleaned the contact pads inside the orange wire's fuseholder, and the tube filaments glow but you still get no sound; think back to when you plugged in the speaker and the amp died. If you plugged that speaker in while the amp was powered on, there's a very strong possibility that the OT is fried. Gil... Link to comment Share on other sites More sharing options...
neosporran Posted December 22, 2008 Share Posted December 22, 2008 supersoldier let me know if any of this helped you fix the amp. I am having the exact same problem. Unplugged everything to change the preamp tube and now it will not work. Good new tube. Old tube would not work either when I put it back in. Link to comment Share on other sites More sharing options...
Eracer_Team Posted December 22, 2008 Share Posted December 22, 2008 okay look at this picture: http://www.diycustomamps.com/images/vj/voodooVJ/voodooVJ_chassis2.jpg notice the nice gold colored transformer.. notice the white tubes with blue and orange wires going into them. Those are fuse holders. They push in a bit and twist open, inside is a glass buss fuse. There are little brass contacts that touch the glass buss fuse, these tarnish and nolonger make contact which is/are needed for the heaters to run your tubes. The easiest way to tell if you have a problem here is to look at the tubes when the power (and speaker attached) is on. Does the tubes glow, this is a yes or no answer. If the answer is no the tubes don't glow(one is incased in a metal cover which can be taken off and left off btw) then the first thing is to turn off the amp and unplug it, now remove the back cover and open the fuse holders. Use the tip of a small screw driver or a little sandpaper and scrape the brass contacts of the fuse holders and put the fuse/holder back together.. NOTE: the fuses in the blue line are different than the orange lines, don't mix them up. once you've done this put the speaker back on and power up and re-look at the tubes and do they glow. If you've started changing the tubes then as the guys suggested you could have created more problems, first of which is did you bend a pin. Link to comment Share on other sites More sharing options...
m-theory Posted December 22, 2008 Share Posted December 22, 2008 Remind me not to have you guys swap tubes in my amps, ok? Joking aside, it is very easy to bend those pins when you put one of these little tubes in. Hard to say if that's what's going on or not, but I've done it myself, so I know it's possible to do. Link to comment Share on other sites More sharing options...
neosporran Posted December 22, 2008 Share Posted December 22, 2008 Did not bend a pin. We did use a tube pin straightener thing at the shop to make sure. I did change the fuse. I have scraped it up, but will do some sandpaper tonight. I will also sand the brass jobs in the fuse holder, I did not scrape those up. Tubes do not glow. What are the 2 blue wires coming out of the PT? Seems like they do not go anywhere. Link to comment Share on other sites More sharing options...
Eracer_Team Posted December 22, 2008 Share Posted December 22, 2008 you don't need to scrape the fuse just the brass tabs in the fuse holder itself. you maybe able to push the wire out a bit for better access. yeah the blues don't do anything in North AM. Link to comment Share on other sites More sharing options...
strangedogs Posted December 22, 2008 Share Posted December 22, 2008 I cut the 2 wires going to the fuse holder - Hooked em together and all was well... then I picked up a real fuseholder to replace it with from Radio Shack. Not a good idea to run it long without a fuse I suppose but it didn't hurt anything. I've never blown a fuse - just the fuse holder was CRAP. Link to comment Share on other sites More sharing options...
cGil Posted December 22, 2008 Share Posted December 22, 2008 It'd probably live for a long time without a fuse on the heaters. VJr is a rare beast in that respect. Not a lot of amps even have a fuse on the heater supply! It's probably got more to do with the low voltage rating of the C12 filter cap than anything else. Gil... Link to comment Share on other sites More sharing options...
neosporran Posted December 23, 2008 Share Posted December 23, 2008 It ended up being the fuse holder. Sanded them down and all is well. Thanks all for your help. Saved me. Link to comment Share on other sites More sharing options...
m-theory Posted December 23, 2008 Share Posted December 23, 2008 Man, that's a common point of failure on these amps, isn't it? You'd think that after this long, and after undoubtedly seeing thousands returned as "defective," they'd have figured out a way to prevent this by now. Link to comment Share on other sites More sharing options...
m-theory Posted December 23, 2008 Share Posted December 23, 2008 It'd probably live for a long time without a fuse on the heaters. VJr is a rare beast in that respect. Not a lot of amps even have a fuse on the heater supply! Not to mention that it's probably rated about 3 amps too high anyway. When I finished my EL34 turret build, I had my amp tech buddy put it on his scope to get the bias dialed in, and he found that the amp wasn't even drawing .5 A, yet has a 2A slow blow as a main fuse...might as well be a piece of tinfoil, for all the good it'll do when it's needed. He recommended I try a .5 A, or at least go to a 1A fast blow. It's probably got more to do with the low voltage rating of the C12 filter cap than anything else. That's probably true...I wonder why they went with such a low rating on that cap? That seems unnecessarily dicey to me. I went with 100v when I did the turret build. More than necessary is a good rule of them in all areas except fusing! Link to comment Share on other sites More sharing options...
strangedogs Posted December 23, 2008 Share Posted December 23, 2008 at one time I was going to try to buy all the ones I could find on Ebay that said "DEAD" as I felt most (if not ALL) were just fuse holder issues. I've seen some sell for $25... Link to comment Share on other sites More sharing options...
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