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Messages - Enzo
« on: Today at 04:18:58 PM »
Yes, running a 4 ohm load on an amp rated only to 8 ohms is overloading the amp. If you keep having to reset the circuit breaker, that should be a clue the amp is not happy. And you should stop doing that before the amp is damaged, if it is not already damaged.
It is LEAST likely to be a transformer, and there is no "worse" after a transformer on the failure list.
You may have worn out the breaker, but it isn't the breaker's fault. YTou need to stop overloading the amp, then we need to determine if the amp has suffered some damage causing it not to power up.
« on: Today at 04:13:44 PM »
Mark, I was not assuming anything, I was making a joke based upon Roly's post just above mine. Perhaps you overlooked the soundstaging reference, clearly satirical, since the Pignose is not a stereo amplifier.
But if you want to be serious, then if you replace defective TIP41s with good TIP41s, then sure it will sound better. The way your post was written made it appear you were attributing the sound improvement to the TIP41C versus TIP41, as opposed to attribtuing it to a good versus bad transistor.
And THAT was what Roly and I were responding to.
« on: Today at 12:17:48 PM »
Oh come on, The TIP41C will better handle the 100v transients than the TIP41. Improves the stereo soundstaging.
« on: May 18, 2013, 03:54:26 AM »
First a note on zeners. They do run warm, and their dropping resistors too usually. If you replace a 1 watt zener with say a 5 watt zener, your dropping resistor may not allow sufficient current to insude the thing "zenes." It probably will never bother you, but zeners rely on a certain amount of currne flowing to maintain a steady voltage. The higher the wattage the more current needed for this.
Make it do it. Now you have the symptom. The symptom is the most valuable troubleshooting tool you have. Don't turn the amp off. We know power cycling will bring it back, but leave it in this state. Ball; up your fist and whack the top of the amp. Does that make it wake up?
Isolate the problem. When it is like this, turn the reverb up partway and rock the amp to crash the reverb springs. Is that loud and normal or is it also diminished? The reverb return is after the preamp, so it tests the power amp.
SInce it does this in the phones, I am not sure how you decided that was a preamp problem. The phones are driven by the power amp. Whatever comes out the speaker should also come out the phones. The problem could be anywhere.
My schematic is fuzzy, but in the power amp, bottom center, is R38 (I think) and C24. Whatever number resistor joins C24. It is 10 ohms. Make sure it is not open. If it opens, then the amp can break into oscillation. And that will sap the power in large manner. Those two parts are your stability network or "zobel'.
Is the reverb up inside the chassis or is it a regular reverb pan with the two jacks on the side? You can play into the input and see what shows up on the reverb drive to the spring unit. Likewise the return from the pan is a convenient point to inject a signal. Divide and conquer.
Got a scope? If not, got some other amp handy? Look up "signal tracer" and make one. It amounts to a probe with a series cap plugged into some amp. You then probe a circuit with signal running throuhg it, and the tracer lets you hear what is going on at that point.
And look up "RF probe" - a very simple thing made of a diode, a small cap and a resistor, and you use it with your meter. Your volt meter will not respond to high frequencies, but this little circuit lets you measure levels of RF voltage. If the amp is oscillating, that is what you have at the output - RF.
« on: May 17, 2013, 07:21:10 PM »
A store might have a good return policy, but that only helps you at the outset. Chances are six months later, no one will take it as a return. SO you might also consider support. Peavey has repair stations everywhere - I am one of them. So does Fender - I am one of those too. SO warranty or after warranty, you can get them serviced. Now, go look up where the nearest authorized repair stations are for Acoustic and Behringer. They may tell you to box it up and ship it to them, but unless you kept the box, ever try to find one to fit a 2x12 combo amp? Not to mention the $30-50 shipping cost. Or you may luck out and be near one of their few places.
Call Peavey or Fender and ask for a schematic so your local tech can work on an amp. They'll send it to you in minutes. Now call Behringer and ask for a schematic. No dice. Peavey will sell any part to anyone who calls. Most other companies won't, they refer you to their dealers.
Age of an amp is not nearly as important as condition. There are PLENTY of guys gigging regularly with 30 year old amps. There are 2-3 year old amps that are beat into junk. As a tech I don;t care what year an amp was made, I leave that for the amp fans to obsess over. I do care what revision version an amp is of course, because the circuits change.
It makes a difference what you want to play. A pedal steel cat wants a different amp from the Metallica tribute band.
Try as many amps as you can. I like Peavey as a company, and recommend their amps a lot. The Bandit is one of the worlds most popular amps for a reason. SOunds good, works well, is well supported. Might not be a 2x12 or 100 watts, but worth a look.
Now just my own opinion on the DSP stuff. Ever get one of those multi-effect pedals like DOD makes? Got a hundred patches, and every effect you can imagine. And at first it is exciting to run through all the patches. But after a short while, you wind up using three of them and rarely any others. SOme of the entry level DSP amps do this as well, in my mind. And modelling itself is a compromise. You get a switch to select Fender Twin, Marshall Plexi, AMpeg something,or whatever. And sure enough, the amp sounds kinda like a Twin and kinda like the Marshall and kinda like whatever it says it is. But no one would confuse the sound and dynamics with the real original. Like the Metallica or Beatles tribute bands don;t really sound just like Metallica and the Beatles.
On the other hand, the drunks dancing in front of you in the club gig don;t care. SO if your multi-modeller sounds close enough to whatever cover tune you are playing, that's good enough. I guess my point is not to be overly impressed at all the modelling and DSP, consider those in terms of the gig it will be used in.
Entry level amps are just that. Aimed at players early in their career. The stuff tends to be not as robust as the more pro stuff. tends to be feature laden, with extra eye and ear candy.
« on: May 16, 2013, 06:12:53 PM »
A heat gun, or borrow the wife's hair dryer. Bonus, hair driers are far less hot than heat guns.
« on: May 16, 2013, 06:10:12 PM »
Hi, good form would be to link us to the schematic you are using.
The center tap is at 700v, which means the power tube plates are at 700v. The 350v is on the screens.
The power tubes are cathode driven, so any current through the transistors is also coming through the tube.
« on: May 16, 2013, 06:04:13 PM »
But you might learn more by finding out what was/is wrong with the fan supply, even if you replace it with something else.
So when you called Fender to ask if they still have part number 0055692000 they said no? (I forget, you did say 120v, right?)
« on: May 15, 2013, 01:15:48 PM »
One can grasp each filter cap amd wiggle it. If the hum comes and goes when you do that, you have a loose connection of some sort. A loose connection is usually cracked solder, which we simply resolder. But the wire lead from the cap might be broken, or the copper lines on the pc board might be cracked.
An even simpler test would be to ball up your fist and whack the top of the amp - no disassembly required. If that stops or starts the hum or indeed if the amp reacts at all, that tells us some connection is loose inside. Turn the reverb down when you whack.
One might also just bite the bullet and flip the board over and resolder them regardless of how they appear, fresh solder can;t hurt, and while under there, look close at or resolder the controls and jacks.
While the amp is running, use something insulated, like a wooden chopstick, to push on each part on the board, looking for any that react.
« on: May 15, 2013, 09:39:36 AM »
I don't like PCB Valve gear much.
Can't even get the red knobs off the front on this Fender,
Surely you don't think the knobs were stuck because it is a tube amp? Like the same pots and knobs on a solid state amp would slide right off? Maybe a little heat will help loosen them.
« on: May 15, 2013, 09:35:42 AM »
with just one half of the brown winding working, you still ought to get your 30vDC rails. You could lift D108-111 to remove the fan influence and see if your voltage comes back down.
AHA! I just looked more closely at the schematic, and finally realized what I was seeing. There is a reason the fan circuit does not reference ground. I was trying to figure how the same set of 23v wires could make +/-30vDC or 60v, and still make only 40v in the fan supply.
But it just sank in that the fan supply runs off one of the low voltage wires and one of the high voltage wires. In other words the fan is running off what amounts to a 34-0-23 "winding". Since it has no ground reference, the lopsidedness matters not.
But if one of the diodes in the fan supply shorts, or the C116 or C117, or not swure what else, it would wind up shorting the red wire to the brown wire, and that might be the reason the brown wire haqs burnt open inside the tranny.
1. Lift the four fan supply diodes. Check them while there for shorts. See if the remaining low voltage wire now allows the +/-30vDC down there that would allow the Vregs to come home.
2. Open up the transformer to see if you got lucky and it might be repairable.
3. Solve the fan supply. Look for anything in it that might be shorted.
« on: May 13, 2013, 04:24:57 PM »
Broken solder on a main filter cap comes to mind.
« on: May 12, 2013, 09:27:49 PM »
Yes, one open side of that center tapped brown winding OUGHT to still provide correct DC voltages. I have not yet put any mental energy into it, but it may be possible with that open, the floating fan supply off the same leads is creating an ersatz voltage doubler somehow.
« on: May 11, 2013, 11:40:50 AM »
We may not have the cause and effect figured out, but it definitely is what is wrong at this point.
« on: May 11, 2013, 03:25:26 AM »
And there it is.
The open winding leaving D with no continuity to the rest and zero volts output. Just how that resulted in the one pin having twice voltage I'll have to think about. But the transformer is bad.
Now sincve the transformer has to come out anyway to replace, you might as well try to fix it. It is POSSIBLE the problem is in the lead wires and not th windings. The transformer inside is wound with enamel coated wire, not the colored is=nsulated wires you see coming out. Inside will be some point where the lead wire is soldered to the winding wire. There may be solder terminals you can see from the outside, or they may be buried. We need to go inside enough to see where th brown wire connects to determine if the connection to it has broken, or if the end of the winding wire snapped off right at that point.
And we cannot yet rule out the crimped-on female push connetor on the wire end. Check that joint.
If you have to, you may need to slice open the fish paper (heavy cardboard) around the transformer middle.
Hey, what is there to lose?