Members Guiary Posted June 11, 2008 Members Share Posted June 11, 2008 Hello all, I was wondering if I could score some guidance on my situation? I've replaced R1 and R2 on the preamp board to 220K/1M resistors (they were 100K/1M) and changed R27 to 82K (was 100K).... Prior to that I swapped out the brite cap to a 56K resistor but it worked after that mod. After the latest two I'm not getting any power to the amp I have yet to see if I blew a fuse or 4 but just from a quick check there are two on the board which are not blown and another two (including the one on the back of the amp) which covered in white so I can't see if they're blown. I may just replace those tubes first and then go through my soldering work and make sure it's all good still. I'm almost positive that the ribbons are the right direction from when I pulled them off.... Any suggestions?!? Thanks, Gary Link to comment Share on other sites More sharing options...
Members rushtallica Posted June 11, 2008 Members Share Posted June 11, 2008 I'd check the other two fuses. If there's not even a power light or any sign of power at all then changing the tubes likely won't have any effect, though looking for any resistor or tube socket that looks trashed is worth a go. Try another power outlet/jack if you haven't already, as well. Maybe someone will come along who has some other ideas or familiarity with how changing the ones you have could possibly pose a problem. Link to comment Share on other sites More sharing options...
Members exafro Posted June 11, 2008 Members Share Posted June 11, 2008 Do you have a meter? Checking the fuses only takes a second with one. Link to comment Share on other sites More sharing options...
Members Guiary Posted June 11, 2008 Author Members Share Posted June 11, 2008 I haven't checked the fuses just replaced them and still nothing.... I'm honestly baffled, maybe I'll post some pics and see if someone can point out my {censored} up. Link to comment Share on other sites More sharing options...
Members JerryP Posted June 11, 2008 Members Share Posted June 11, 2008 Gary,Where are you measuring for power? Are the tubes heating up? Do you have any power at the other preamp tubes that you didn't touch? R27 is a feedback resistor and won't affect the power supply. R1 and R2 are plate resistors and will affect power to the first preamp tube. I would double check the solder work to be sure there are no blobs of solder shorting across circuit traces.Jerry Link to comment Share on other sites More sharing options...
Members JerryP Posted June 11, 2008 Members Share Posted June 11, 2008 Those resistors were 100K 1W not 1M. A half watt resistor will work fine in that spot.Jerry Link to comment Share on other sites More sharing options...
Members Guiary Posted June 11, 2008 Author Members Share Posted June 11, 2008 Gary, Where are you measuring for power? Are the tubes heating up? Do you have any power at the other preamp tubes that you didn't touch? R27 is a feedback resistor and won't affect the power supply. R1 and R2 are plate resistors and will affect power to the first preamp tube. I would double check the solder work to be sure there are no blobs of solder shorting across circuit traces. Jerry Neither the power tubes nor the preamp aren't heating up. That's the thing I don't understand, I didn't touch anything on the power side of things. The only tubes that (I assume) would be effected would be V1 and V4 since that's the only areas I was in + according to my awesome schematic reading skills:lol: Link to comment Share on other sites More sharing options...
Members Guiary Posted June 11, 2008 Author Members Share Posted June 11, 2008 Those resistors were 100K 1W not 1M. A half watt resistor will work fine in that spot.Jerry oops maybe I need glasses. Link to comment Share on other sites More sharing options...
Members Guiary Posted June 11, 2008 Author Members Share Posted June 11, 2008 The Pics: Link to comment Share on other sites More sharing options...
Members JerryP Posted June 12, 2008 Members Share Posted June 12, 2008 That 8A fuse in the middle of the power supply board right next to the 4 wire ribbon cable that connects to the preamp board is the heater fuse. Check that 4 wire ribbon cable and the ribbon cable right near it that connects the preamp board to the power amp board. The cable that connects the preamp board to the power amp board is notorius for burning up and causing the power tubes to lose their heater supply. Take a look at that hum balance pot and the cap down on that end of the power amp circuit board too. That is all related to the heater circuit.I don't see any obvious problems in the pics.Jerry Link to comment Share on other sites More sharing options...
Members guidedbyechoes Posted June 12, 2008 Members Share Posted June 12, 2008 That 8A fuse in the middle of the power supply board right next to the 4 wire ribbon cable that connects to the preamp board is the heater fuse. Check that 4 wire ribbon cable and the ribbon cable right near it that connects the preamp board to the power amp board. The cable that connects the preamp board to the power amp board is notorius for burning up and causing the power tubes to lose their heater supply. Take a look at that hum balance pot and the cap down on that end of the power amp circuit board too. That is all related to the heater circuit.I don't see any obvious problems in the pics.Jerry I forget. Resistors aren't polorized? Are they. Link to comment Share on other sites More sharing options...
Members Guiary Posted June 12, 2008 Author Members Share Posted June 12, 2008 Hey Jerry, When I flip the amp on the LED in the front doesn't come on either, now if one of those two ribbon cables were faulty would that also cause no power to the front LED's? Thanks again for your help too! Link to comment Share on other sites More sharing options...
Members Ryan_F Posted June 12, 2008 Members Share Posted June 12, 2008 I had several problems with my ribbon cables, definitely give em a good checkover. The problem seems to be located in the power supply board, or interconnecting ribbon cables. Take your multimeter on continuity and test all fuses, they can be blown while looking good yet. sidenote: wow your vtm looks clean on the inside. Mine was covered with brown sludge of some sort and a million cobwebs. Link to comment Share on other sites More sharing options...
Members Guiary Posted June 12, 2008 Author Members Share Posted June 12, 2008 Ok problem figured out... Umm I feel a little stupid telling you all but here we go, I severed the power cable:poke:. The only time I think it could've happened is when I flipped the amp over and the cable was under it, with a light tug out came the cable and damage free I thought. Well I was wrong. Anyway how does it sound? I think adding two of the 220K resistors might be alittle too much, Im going to stick one of the 100K's back in there and see how that sounds, but it seems to have a bit too much, I don't know, lack of clarity or not defined enough... It almost sounds like at times it has too much bass then at others sounds like too little. Before I try anything else I'm going to try it on a slant cab rather than the straight. Link to comment Share on other sites More sharing options...
Members Numb Sensitive Posted June 12, 2008 Members Share Posted June 12, 2008 I had several problems with my ribbon cables, definitely give em a good checkover. The problem seems to be located in the power supply board, or interconnecting ribbon cables. Take your multimeter on continuity and test all fuses, they can be blown while looking good yet.sidenote: wow your vtm looks clean on the inside. Mine was covered with brown sludge of some sort and a million cobwebs. Brown sludge. Isn't that what happens when caps explode?? Link to comment Share on other sites More sharing options...
Members the Gibonator Posted June 12, 2008 Members Share Posted June 12, 2008 Now that you have the power problem figured out, what do the mods do and let us know what you think of the sound after you're done. Maybe I'll try them on my VTM 60 Link to comment Share on other sites More sharing options...
Members Guiary Posted June 12, 2008 Author Members Share Posted June 12, 2008 I'll be trying out a couple more things first but I'll for sure post up my findings and if I get the chance to some clips!!! Link to comment Share on other sites More sharing options...
Members Ryan_F Posted June 13, 2008 Members Share Posted June 13, 2008 I dont think the brown sludge was from caps exploding, it was there before the caps blew up on me. Let us know what other mods youve done and what their results are. Also, did you ever try the Gain 2 cap replacement? Link to comment Share on other sites More sharing options...
Members rushtallica Posted June 13, 2008 Members Share Posted June 13, 2008 Ok problem figured out... Umm I feel a little stupid telling you all but here we go, I severed the power cable:poke:. The only time I think it could've happened is when I flipped the amp over and the cable was under it, with a light tug out came the cable and damage free I thought. Well I was wrong. Anyway how does it sound? I think adding two of the 220K resistors might be alittle too much, Im going to stick one of the 100K's back in there and see how that sounds, but it seems to have a bit too much, I don't know, lack of clarity or not defined enough... It almost sounds like at times it has too much bass then at others sounds like too little. Before I try anything else I'm going to try it on a slant cab rather than the straight. Glad to hear you got it worked out. Good luck on the resistor changes doing what you're wanting. Link to comment Share on other sites More sharing options...
Members Guiary Posted June 13, 2008 Author Members Share Posted June 13, 2008 I dont think the brown sludge was from caps exploding, it was there before the caps blew up on me. Let us know what other mods youve done and what their results are. Also, did you ever try the Gain 2 cap replacement? I decided to skip that gain 2 cap replacement (for now) cause according to the manual when gain switch 2 is activated it opens that extra gain stage so I figured (also got help from someone in another forum) that if I'm looking for an overall increase of gain that I should swap out the two 100K resistors (R1 and R2 from the preamp board) and that when I want a total increase flick on gain switch 2 and magic gain!.... But I think adding the two 220K resistors to both R1 and R2 kind of make the amp sound like it has a stomp box distortion:freak:. But after playing around with things gain switch 1 off and gain switch 2 on it didn't sound half bad! I still wanna try my idea and see how that sounds. Also for the hell of it I'm going to stick the extra 220K resistor I have (after swapping the original 100K back to R1) in the R8 spot. The biggest problem I'm having is trying to give the amp more "umpf" or "girth", so any suggestions would be awesome! Thanks Gary Link to comment Share on other sites More sharing options...
Members Guiary Posted June 13, 2008 Author Members Share Posted June 13, 2008 Glad to hear you got it worked out. Good luck on the resistor changes doing what you're wanting. Thanks for the luck! I think I'll need it! Link to comment Share on other sites More sharing options...
Members the Gibonator Posted June 13, 2008 Members Share Posted June 13, 2008 The biggest problem I'm having is trying to give the amp more "umpf" or "girth", so any suggestions would be awesome!ThanksGary Have you tried a eq in the fx loop? It made my amp much more articulate and the sound was much more to my liking. Link to comment Share on other sites More sharing options...
Members Guiary Posted June 14, 2008 Author Members Share Posted June 14, 2008 Have you tried a eq in the fx loop? It made my amp much more articulate and the sound was much more to my liking. I have an EQ available but I want to get a good base sound first... I try to use very little effects etc which would be on at all times. I'll use an EQ for certain songs, leads, etc, but prefer nothing but natural. I'm not saying that the VTM doesn't sound good, it's just that I wanna try to modify an amp. The VTM seems to be a good stepping stone into learning. Just curious would it be safe using KT66's in place of the 6L6's in the amp currently? I heard (from searching around) that it might add that girth I'm looking for. BTW (all on the preamp board) Sticking R1 back to 100K (original)and putting that extra 220K in R8 (I think, it's the one that's next to V2) Made a good improvement in the sound! Also swapped the 10uf Cap on C10 to a 22uf/50V Cap. I think it helped things out a little also it's switchable! Still thinking of what else to try... Oh the preamp tubes I really hate what I have in there but untill I get paid next I'm stuck with it. Plan on trying a Mullard in V1 and Penta for V2 and V3 and then some Chinese for V4. Gary Link to comment Share on other sites More sharing options...
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