freakinawesome Posted January 11, 2009 Share Posted January 11, 2009 Hey just completed the fendery mods tonight,checked the numbers which seem to look alright. The problem is there's no volume til about 12o'clock,then I can hear some great tones but volume all the way up it is really quite quiet. It's about as loud as it was stock (V3) just barely at 7o'clock - but sounds really good! I'll post the numbers on the moro,but for now is this a common problem that i've missed due to my newb-like status? Also changed the volume pot with an alpha 1meg 24mm pot.Using JJ pre and power thanks chaps Link to comment Share on other sites More sharing options...
TWANG Posted January 11, 2009 Share Posted January 11, 2009 is your pot in backwards? TWANG Link to comment Share on other sites More sharing options...
freakinawesome Posted January 12, 2009 Author Share Posted January 12, 2009 I don't think so,no.I just copied what was on the original pot. Looking from inside the chassis with the three lugs on the bottom I have (left to right) white red black I've been searching the net but no-one has this same problem apparently](*,) Link to comment Share on other sites More sharing options...
layboomo Posted January 12, 2009 Share Posted January 12, 2009 double post sorry! Link to comment Share on other sites More sharing options...
layboomo Posted January 12, 2009 Share Posted January 12, 2009 Try simply taking the pot out and scuffing up the metal around the hole with a small piece of sand paper and re install the pot.......you may just have a bad chassis ground connection. Link to comment Share on other sites More sharing options...
freakinawesome Posted January 12, 2009 Author Share Posted January 12, 2009 Found this in an earlier post but not sure how it relates,does anything here sound common? Faulty Preamp Tube Faulty Power Tube(s) Bad preamp cathode resistor An unbypassed cathode resistor has drifted upwards (to 5K-10K or over) Faulty phase inverter If for some reason the phase inverter input side is good but the inverted side is bad, the power amp will still work, but power will be very low. This can be a bad 1/2 tube, a faulty socket contact, a broken or open plate resistor or coupling capacitor to the output tube, or a bad solder joint on any of these. Open cathode bypass capacitors in preamp if they go open, the stage they're in loses gain, but does not otherwise fail. If they short, it dramatically shifts the bias point, and may cause distortion as well as low volume. Faulty vibrato circuit on neon/LDR vibrato Fenders If there is a dummy plug in the footswitch hole, or a bad footswitch so the vibrato is always active, sometimes the vibrato tube turns on and stays on, not oscillating. This keeps the neon bulb on all the time, shunting lots of signal away. Same thing can happen if there is a shorted vibrato tube (rare) or a bit of wire or solder shorting the vibrato tube. Check the plate voltage on the vibrato tube to be sure it's oscillating. High voltage isn't high enough for some reason Failing rectifier tube - try swapping in another one Failing power filter capacitors Failing or open series dropping resistor in the bypass networks leading to preamp stages Failing bypass capacitor - treat as in power filter caps. Open screen resistors on power tubes Amp cuts out or "goes dead" when the volume control is turned up higher than "X" or when you hit a specific note You have a parasitic oscillation above hearing range. This can overheat an output transformer, and really needs to get fixed fast. It can often be fixed by tube swapping, but you often need an oscilloscope to see what's happening in the electronics. Link to comment Share on other sites More sharing options...
Eracer_Team Posted January 12, 2009 Share Posted January 12, 2009 well since you've completed some mod's it sounds like you've had a soldering iron in your hand... which by assumption you should also have a DMM. Take the standard voltage reading for us and that might help too (but don't rule out that you soldered something to the wrong spot) so start with the wall a/c, then both sides of R10,R12, R13. then pins 1,3,4,5,6,8 of the 12ax7 and then pins 3,7,9 on the el84. if this is not a turret board you can check all referenced to ground in DC, if it's a turret board. pin 4,5 on both tubes will be in a/c and you'll need to switch to that setting for the heater lines. Link to comment Share on other sites More sharing options...
freakinawesome Posted January 14, 2009 Author Share Posted January 14, 2009 well since you've completed some mod's it sounds like you've had a soldering iron in your hand... which by assumption you should also have a DMM. Take the standard voltage reading for us and that might help too (but don't rule out that you soldered something to the wrong spot) so start with the wall a/c' date=' then both sides of R10,R12, R13. then pins 1,3,4,5,6,8 of the 12ax7 and then pins 3,7,9 on the el84. if this is not a turret board you can check all referenced to ground in DC, if it's a turret board. pin 4,5 on both tubes will be in a/c and you'll need to switch to that setting for the heater lines. [/quote'] Cheers for the instructions. It's just the stock PCB so decided not to go with the turret board. I just took the readings so hopefully it will discover something simple! 12AX7 Pin 1 158.6 Pin 3 1.2 Pin 4 5.9 Pin 5 5.9 Pin 6 140.6 Pin 8 0.72 El84 Pin 3 8.9 Pin 7 284 Pin 9 271 With regards to the resistors I took the readings as if facing the front of the chassis and going from right to left on the board. R10 329 - 298 R12 299 - 271 R13 271 - 250 What ya reckon? Link to comment Share on other sites More sharing options...
Eracer_Team Posted January 14, 2009 Share Posted January 14, 2009 over all voltages look low. esp the el84 pin 3,7,9. with them at 8.9, 284, and 271 you'll have a lot less volume I would think. (your pre-amp side is shade low too... you didn't list the wall a/c at the time which effects the internal voltages but ... what size is R10? But even still the 329 on one side is low, that's usually around 350~370 range You by chance didn't install a lighted standby switch did you? (although that would drop more than just 40v) Might be looking at the 4 1n4007 diodes or maybe even the primary transformer. Link to comment Share on other sites More sharing options...
freakinawesome Posted January 14, 2009 Author Share Posted January 14, 2009 Not sure how to measure the wall a/c but the voltage here is 230. R10 is 2w 680r Only mods I installed were just resistors or caps and the volume control.My V3 was way loud before(too loud for the house) and now a shadow of it's former self,so the low voltages leads to less power and less volume which makes sense. I didn't add a lighted standby either,no. Eventually will be converting to a baby marsh,and I have a Harley Benton GA5h to have a go at in the mean time.Even though this is my first go at modding I can't think it's going to be a serious problem as although the volume is really low it still sounds great! Thanks for the help BTW tubes both light up,EL84 a lot more than the 12AX7 if that makes a difference? Would get some pics up but I don't own a digi cam. Link to comment Share on other sites More sharing options...
Eracer_Team Posted January 14, 2009 Share Posted January 14, 2009 hmmm interesting.. 230 eh? I just ran your voltages through the bias calculator spreadsheet (guessing your r14 is still 220ohms) I get a current of 40.45mA with raw plate dissipation at 11.12905 watts; so that "looks" ok. I would think I would turn my attention to the to your volume pot you installed. maybe with the heat of soldering it you created a "flat spot" on the pot... one way to tell is to put a jumper from R6 to the pin 7 of the 12ax7 (you can find these points on the leg1 and leg 2 of the pot; of course leg3 is pot to ground) do you get full volume all the time? should be yes and it should be as loud as it was (remember that some of the cap's thin out the sound in the 'fender' mod. next pull the pot out and test its resistance, you should see it climb (remember it should be a log pot not a linear pot so it won't be a smooth straight up to 1meg but you shouldn't see any 0,0,0,0.. 100ohm, etc as you turn it. Link to comment Share on other sites More sharing options...
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