stumblinman Posted March 9, 2009 Share Posted March 9, 2009 Hey all, I've recently come across an odd situation with my second VJr I recently purchased from a guy on Craigslist. When I first turn it on and put volume at about 10 o clock or so, it comes out very thin and tinny. But once I turn the volume up past about 2 o clock, it comes back to normal, and then when I turn it back down it stays at the correct volume for that point, not weak and tinny. Any ideas where to even begin? Thanks! I already changed tubes, but as far as where to go on the PCB I'm not even sure where to start. Link to comment Share on other sites More sharing options...
Steven Lister Posted March 9, 2009 Share Posted March 9, 2009 What you described sounds like an improper warm-up problem. Try adding more initial warm up time to give the EL84 more time to cook (+ a sluggish new valve? there are duds)..., ...or your VJr. may have an internal valve heater issue -- one that manages to resolve itself after you have cranked it for awhile -- until it cools off again. Hit every BLUE NOTE baaaby..., I'm going to play on:-" Link to comment Share on other sites More sharing options...
stumblinman Posted March 9, 2009 Author Share Posted March 9, 2009 Hmm.. that is something I never even considered. I've tried different tubes to the same effect. Tonight, it started out working fine at about 10 oclock volume, then after about 5 mins of playing cut out to tinny sounding. Turned it up, it came back. Turned it down and it stayed working. I'm flabbergasted. Although, when I first put new tubes in, it did crackle a little when I'd first start playing. That problem has gone away. So maybe both my EL84's I've tried have the same issue, as both did the crackling at first. I was aiming towards OT or something like that, bad capacitor etc.. I have 2 other EL84s I can throw in. That will be my next step. Any other ideas please keep them coming! Link to comment Share on other sites More sharing options...
layboomo Posted March 10, 2009 Share Posted March 10, 2009 Before you go much deeper into it.......remove the fuse from the holder on the orange wire and scuff the fuse holder contacts with sand paper or an emery board and see if that helps. That was a notorious problem on older VJR'S. Link to comment Share on other sites More sharing options...
m-theory Posted March 10, 2009 Share Posted March 10, 2009 Start by replacing that bad volume pot. That should cure your problem, based upon what I'm reading. Link to comment Share on other sites More sharing options...
m-theory Posted March 10, 2009 Share Posted March 10, 2009 Edited to remove double post Link to comment Share on other sites More sharing options...
mrjones200x Posted March 10, 2009 Share Posted March 10, 2009 Im no electronics whizz but same happened on my guitar volume pot. Had a bad spot that sounded all funny and sometimes would sound ok if you went back and forth a few times. Link to comment Share on other sites More sharing options...
stumblinman Posted March 10, 2009 Author Share Posted March 10, 2009 Ok, going to respond to 2 posts. First, I have no idea where a fuse by a orange wire is. I checked/cleaned the fuse on the back by the power plug. I can open it again and see if there's one inside I guess. You know, that's just how ridiculous I am, I haven't even tried contact cleaner on the volume pot to see if it helps any. That's my next plan of attack. Thanks! Update: Tried the contact cleaner, no go on volume pot. It isn't a quick switch of sound, it's a fade in and out sort of thing. No crackle or anything to indicate a change, just a slow swell and ebb of volume. Link to comment Share on other sites More sharing options...
stumblinman Posted March 11, 2009 Author Share Posted March 11, 2009 Turned it up halfway and just played for about an hour and a half, no problem with volume at all... I'm starting to really think it could be the volume pot. If it were voltage related, wouldn't it be a problem as volume/output increased? Since I didn't spend any time really with the volume in the lower range that seems to cause problems, I'm more inclined to lean towards that, but I still have questions... What are average voltages for the pins on the tubes? Still haven't looked for a fuse by an orange wire, and what pot would I need to replace volume pot? Thanks again guys for all the info on this. Link to comment Share on other sites More sharing options...
m-theory Posted March 12, 2009 Share Posted March 12, 2009 500k audio (or log) pot The orange wire isn't visible from the outside. You'd have to pop the back cover off, and probably pull the chassis in order to get to the fuseholder on it. My guess is still the pot, though. Link to comment Share on other sites More sharing options...
Eracer_Team Posted March 12, 2009 Share Posted March 12, 2009 all the schematics I have for a stock valve junior is 1meg not 500k. Link to comment Share on other sites More sharing options...
stumblinman Posted March 12, 2009 Author Share Posted March 12, 2009 Is it a standard pot, or something different to attach to PCB? Link to comment Share on other sites More sharing options...
Eracer_Team Posted March 12, 2009 Share Posted March 12, 2009 the pot is a little smaller than normal size and its got a little pcb board that its soldered to then a cable runs to the main pcb board. the only time I think I've heard of the pots going bad is when a few of the guys were soldering on them different mod's. Don't think I've heard about too many pots in these guys going bad on their own, but anything is possible. the orange wires coming off the transformer inside is were you'll find the plasitc fuse holders (you'll need to undo the 7 screws on the back and gently pry the back off to see the wires) you push in then twist, there is a glass bus fuse inside and it connects to either end, those ends inside the plastic get dirty and do all sorts of funny things. just scrape them with screwdriver or sand paper. warm up should be just a couple of minutes but you said your problem was after 10+ minutes of playing.. voltages inside the amp very depending on what you get at the wall were you plug it in. That’s why the mod craze started on these guys right here on this forum, most have now moved over to sewatt.com since this site likes removing good information Link to comment Share on other sites More sharing options...
stumblinman Posted March 12, 2009 Author Share Posted March 12, 2009 Thanks Eracer, I actually just noticed the fuse today lol. I'd been looking up by the board, rather than underneath the chassis by the OT. Found it and it looked clean and smooth. Just rubbed it a little and put it back together. Haven't had a chance to test it yet, as I'm coaching Softball for my girls and just got back from practice. I'll give it a whirl and let you know if it helped. Also, thanks for the info about the pot going bad, I was kinda curious about that myself. Usually unless someone dumps an ashtray or something on it, it's hard to imagine it going bad so soon. It's a V3 head too. Considering the guy used an attenuator with it, as he lived in an apartment, I'm sure he had it cranked most of the time, so who knows what may have overheated or just plain worn out. Link to comment Share on other sites More sharing options...
Eracer_Team Posted March 12, 2009 Share Posted March 12, 2009 if it was any other style of amp I'd have to agree about the attenuator slowly cooking the tubes, but since the VJ is an SE class amp the el84 run flat out all the time (unlike push-pull amps). And the EEE over on the other forums have proven with their scopes these amps actually work a little less hard in the current standpoint when run with the volume at 10. the fuse holder, don't be decieved.. scratch em up with the tip of the screw driver. this may not fix you but their are a well known source of problem. Link to comment Share on other sites More sharing options...
m-theory Posted March 12, 2009 Share Posted March 12, 2009 all the schematics I have for a stock valve junior is 1meg not 500k. It doesn't need more than 500k. Those flimsy little pots that come stock on these amps can flake out at any time. They're junk. Could easily be that a bit of the carbon path has just peeled off. Link to comment Share on other sites More sharing options...
Eracer_Team Posted March 13, 2009 Share Posted March 13, 2009 Also sounds like he got it used M. So it could be a lot of things... He's probably going to need to buy a digital multi-meter and pull out some glasses for lots of reading. Link to comment Share on other sites More sharing options...
stumblinman Posted March 13, 2009 Author Share Posted March 13, 2009 That's exactly what I'm leaning towards myself Eracer. It seems to work fine after some warmup, so I guess I can begin the hunt. Where can I find info on all the voltages as well as a v3 schematic? All I am able to come up with is v2 prints and no pinout voltages. I'm probably not looking in the right place or asking the right people (until now) Link to comment Share on other sites More sharing options...
Eracer_Team Posted March 13, 2009 Share Posted March 13, 2009 some of the 'non-modd'ers' got up set with the amount of modd'ing information on this forum (although this forum was the start of the VJ craze), so everyone left for www.sewatt.com There you'll find a whole section of FAQ's. voltage's inside the amp start from what you're feeding it on the outside. If your wall plugs are at 110vac (NA spec) then you're probably very lucky. If your wall runs at 124vac then you'll have way too much voltage inside the amp. Like I said sign into sewatt. Link to comment Share on other sites More sharing options...
m-theory Posted March 13, 2009 Share Posted March 13, 2009 For this specific problem being described, I'd start with that pot. Link to comment Share on other sites More sharing options...
layboomo Posted March 13, 2009 Share Posted March 13, 2009 "...I'm probably not looking in the right place or asking the right people (until now) " Or maybe you just started listening. Go to Sewatt and ask unless they too aren't the right people since many of us frequent both places. Link to comment Share on other sites More sharing options...
stumblinman Posted March 13, 2009 Author Share Posted March 13, 2009 I am registered there, but I don't go there anymore as when I first bought my first VJr, the people there were.. less than hospitable to new VJr guys, so I left and didn't look again. Seems folks here are less apt to outbursts of superiority. But I'll head back there and check for prints etc. As far as the actual statement "I'm probably not looking in the right place or asking the right people (until now)", that was in reference to simply googling for prints and voltage lists, not stating that you guys weren't helping me, so I'm sorry if my statement was misread. I guess that's the problem with text rather than speech. Link to comment Share on other sites More sharing options...
Eracer_Team Posted March 13, 2009 Share Posted March 13, 2009 if you go to sewatt's FAQ section you'll find the schematics for all 3 boards (and you don't have to talk to anyone). http://www.sewatt.com/files/sewatt/StockVJ_1-3.pdf Please read the "how can I work on my amp without killing myself"; BEFORE poking around inside. print out the schematic you need, then start using you dmm. (You will need a DMM that can take 600vdc+, also get auto ranging, last thing you want it to be flipping the dial all over and getting mixed up in different range settings) first switch to a/c and check the wall (and write it down on the schem); this changes sometimes daily/minute or second and it has everything to do with the voltage inside the amp) next Clip the black lead to the ground nut, and switch to DC.. Remember anytime the amp is on, have you speaker connected. I follow around in a counter clock-wise motion.. first go along the voltages of the power supply.. B+, B1+, B2+... also know as R10, R12, R13.. etc.. The go to the tubes,, pre-amp first pin 1, 3, 4, 5, 6, 8, (notice I left off pin 2 & 7).. then to the EL84.. pin 3, 7, 9. then start playing until you hear the sound drop, then retake all you voltages. Did you see any difference in places? You may or may not see difference in voltage.. maybe M-T is right and you have a bad pot... But the voltage's will tell you and us a lot. remember the tongue is very good an detecting temperature but not advisable in a tube amp. Soup yes, Pizza yes Coffee yes.. tube amp no. Link to comment Share on other sites More sharing options...
cGil Posted March 13, 2009 Share Posted March 13, 2009 I am registered there' date=' but I don't go there anymore as when I first bought my first VJr, the people there were.. less than hospitable to new VJr guys, so I left and didn't look again. Seems folks here are less apt to outbursts of superiority. But I'll head back there and check for prints etc. [/quote'] Way back when, SEwatt did have a troll or two, but they've moved on to tormenting folks elsewhere, like at disHarmony Central. SEwatt's actually been a friendly and peaceful forum for quite a while now, and we're getting a lot of stuff done and making good advances in the name of tone. The closest thing I've seen to an actual confrontation in months was in the Computer Recording threads on Watkins' (SEwatt) Community Center, and even that mellowed without intervention before a brawl broke out. Personally, I think the current crowd you'll find on SEwatt is one of the most mellow and helpful bunch of folks you could ever hope to run across. As a voluntary moderator over there, I do less work than the lonely Maytag repair guy. I give 'em a solid 4.0 thumbs up! Gil... Link to comment Share on other sites More sharing options...
layboomo Posted March 13, 2009 Share Posted March 13, 2009 I am registered there' date=' but I don't go there anymore as when I first bought my first VJr, the people there were.. less than hospitable to new VJr guys, so I left and didn't look again. Seems folks here are less apt to outbursts of superiority. But I'll head back there and check for prints etc. As far as the actual statement "I'm probably not looking in the right place or asking the right people (until now)", that was in reference to simply googling for prints and voltage lists, not stating that you guys weren't helping me, so I'm sorry if my statement was misread. I guess that's the problem with text rather than speech.[/quote'] Well it did seem a little snotty as written,but I see what you were saying.....it doesn't always come across the way you mean it in these forums agreed! I've had that problem on a few occasions myself and had to apologise for what I thought I said........or when it was taken the wrong way. No problem and thanks for the explanation. In all honesty SEwatt is a much different place now than it was in the early days and I think you ought to give it another shot. All of the guys over there genuinely like sharing ideas and helping people.......sure they trade zings once in a while....but that keeps it fun too. The only thing I'll caution you on is that building and hot rodding amps gets addictive fast and pretty soon you'll go from just fixing one to building 3 or 4! Good Luck with your amp! Link to comment Share on other sites More sharing options...
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