i have a fender champion 600 that i modded...basically bypassed the bassman style tone circuit to get raunchier tones and a bit more volume. so today i was playing it cranked through a 12" speaker and all was well....then i kicked on a fuzz. no bueno. it sort of cut out for half a second and then sounded darker. i turned the fuzz off and just strummed a bit to see if it sounded ok. then i thought maybe i'm crazy and maybe it's all good. turned the fuzz back on (which was set pretty tame) and then it just cut out completely.
it still powers up, tubes lit and all, but no sound. i swapped the preamp and power tubes and nothing. i've blown a fuse on an amp....blown a speaker on an old vibro champ by running a big muff into it, but never actually blown an amp. what should i be looking for? nothing seems obviously fried on the inside. i don't have a ton of experience working on amps, but my gut tells me maybe it's the output transformer? any opinions? how would i go about testing the transformer itself?
thanks so much in advance.
daniel
> my gut tells me maybe it's the output transformer?
Don't listen to your gut.
It is almost never the OT.
The OT (and PT) is the *last* thing you "want" to replace. Aside from the costly metals, the shipping is brutal.
Put your ear in the speaker. Is there ANY hiss/hum? If so, it ain't dead, and is likely minor.
Replace the power bottle (6V6 IIRC). Repeat ear-test.
Jiggle wiggle all connectors, specially speaker.
Try another speaker (use alligator-clips if it isn't plug-in).
A 600 is small. Kick it across the room. If that makes it work, you KNOW it is a bad joint and you KNOW it will crap-out again, so you gotta fix it.
(Since you have already been inside) Open it up and look for a problem. With this history, I would cast a very sceptical eye at your tone-stack mods-- the solder, any connectors, the solder, and especially the solder joints.
it is dead silent...nothing coming from the speaker. i tried it both thru the 12" i was originally playing thru and its own internal 6" speaker. nothing. replaced preamp and power tubes and nothing. so yeah...next i'll start wiggling things around. i really feel like it was a result of the fuzz pedal overloading it though, rather than something shaking loose, especially since i was running it thru an external cab, but i'll go ahead and reflow the solder joints tomorrow.
bypassing the tone stack bumps the volume up quite a bit...could that have any ill effects on any part of such a simple amp design? the only reason i blindly suspect the OT is that it's a $150 made in china 5 watt amp. i'm assuming they're not using top notch transformers.
On several amp forums, I've noticed a tendency for posts that go like:
"My amp is [whatever symptom it has]. It's the output transformer, isn't it?"
It happens often enough that I'm thinking of coming up with a syndrome name for it. :icon_lol:
The urge to believe that an output transformer is dying in an amp is baffling to me; perhaps it's related to Intern's Disease.
Do the tube heaters glow?
+1 to Gus's question.. If you know how to SAFELY measure the voltages in the amp, all the critical voltages are in the schematic, which is on Fender's site.
Quote from: R.G. on August 28, 2015, 11:27:20 AM
On several amp forums, I've noticed a tendency for posts that go like:
"My amp is [whatever symptom it has]. It's the output transformer, isn't it?"
It happens often enough that I'm thinking of coming up with a syndrome name for it. :icon_lol:
The urge to believe that an output transformer is dying in an amp is baffling to me; perhaps it's related to Intern's Disease.
Maybe because it's one of the more expensive parts, which we've heard such doom and gloom about?? Jumping to the worst outcome?
"We're all doomed, I tell ya!" ;)
Altho, if it always WAS the OT, it would make for a LOT easier debugging!
Maybe it's a bad solder joint from your mod. You cranked it, the vibration made the solder joint fail and now it's quiet. Investigate the area of the mods.
Quote from: R.G. on August 28, 2015, 11:27:20 AM
On several amp forums, I've noticed a tendency for posts that go like:
"My amp is [whatever symptom it has]. It's the output transformer, isn't it?"
It happens often enough that I'm thinking of coming up with a syndrome name for it. :icon_lol:
The urge to believe that an output transformer is dying in an amp is baffling to me; perhaps it's related to Intern's Disease.
haha, honestly i don't have all that much experience working on amps. i've done mods here and there and rebiasing, but that's pretty much the extent of it. i don't really know why i thought it was the output transformer...no real logic behind it other than the amp seems fine other than there being no sound.
the tubes are glowing just like normal and the fuse isn't blowing...it definitely sounded like it was directly related to being overloaded with the fuzz pedal...as in i'd never had a problem with the amp in the past and the pedal did seems to make things weird. i won't be able to grab the amp until tomorrow, but i'll definitely check the schematic and measure voltages.
i never thought slamming an amp input would do much more damage than wear the tubes out faster so this is weird.
You might want to look at this link from geofex.com:
http://geofex.com/ampdbug/ampdebug.htm (http://geofex.com/ampdbug/ampdebug.htm)
hm,mmm.... tone stack bypass, gain ya a good 6 db or so... or twice as much "volume"...
no sound at all, everything lights up.
you didn't say if you tried a different speaker. it is a very real possibility that by bypassing the tone stack you are allowing unfiltered dc thru where it should be blocked.
hitting the amp harder can make the amp louder. if the speaker can't handle the spikes, it can pop fairly easily. put a 9v battery across it's terminals to ensure the speaker survived.
next, check the leads from the amp's output to the speakers. i've seen them melt internally and either open or short.
like everyone else says, take a look at your "mods". 10 bux says that's the root of your problem.
get a copy of the schematic, and for @#$%s sake be careful man, it's a @#$%ing tube amp, and the voltages can be LETHAL. not to be a pompous asshole, dude, but if you don't know your way around inside an amp enough to do more than biasing it, you shouldn't try to mod it. it's not a solid state circuit, and some mods can @#$%in kill you. seriously. like a heart attack. i think most of us who have gotten a good zap across the chest will agree, it's not a great way to enjoy your day.
check the speaker. check the cord. turn the amp off, discharge the caps and leave a drain to ground from the ct of the ot DO NOT FORGET TO REMOVE BEFORE POWER UP and undo your mods. odds are you'll get the amp working again.
draw up a schematic of what you did and how you did it. pictures, etc. and post back here. if you DID let too much voltage thru in some areas you may have cooked some components. not entirely likely, but without seeing what you did and the schematic it's kinda hard to speculate.
good luck man. keep one hand in your back pocket for me, a'ight?
I hate to be "that guy," but have you tested the tubes? I've had a couple amps that I worked on that when even one preamp tube is starting to go the whole amp will start to sound like garbage or will make no sound at all. Just a thought.
He's checked out the tubes and speakers...
Quote from: ode2no1 on August 28, 2015, 01:09:47 AM
it is dead silent...nothing coming from the speaker. i tried it both thru the 12" i was originally playing thru and its own internal 6" speaker. nothing. replaced preamp and power tubes and nothing. so yeah...next i'll start wiggling things around. i really feel like it was a result of the fuzz pedal overloading it though, rather than something shaking loose, especially since i was running it thru an external cab, but i'll go ahead and reflow the solder joints tomorrow.
actually LOOKING at the schematic helps immensley.
the "tone stack" is preset, and has blocking caps rated at 400v. if you removed this part of the circuit, you had the full b+ voltage of the amp going right into the input of your volume control. seeing as how it should only be seeing AC of only x number of volts, and is probably a 1/4 amp rated pot, i'd bet you melted the mofo inside. without the caps in the "tone stack" there are no blocking caps to protect the rest of the circuit.
so you would have got a huge volume increase, a peculiar weird muffled distortion that would sound way more ballsy than the stock circuit, and as the pot burned out, a tonal change up until total failure.
take a 400v cap and put it in series with the output of the first stage.... in other words, plate of v1 needs a 400v cap going to the input of the volume control, and of course REPLACE the volume control... and you should be back in the running, sans tone stack. make the cap something that can handle the voltage, first... worry about tone AFTER you get it running.
i am very grateful you didn't hurt yourself doing this. you can really f yourself up not realizing you're being electrocuted. i have neuropathy in my hands that tends to make them numb and tingly... sometimes i've mistaken low level electrocution for this.
anyways... here's a schematic:
http://support.fender.com/schematics/guitar_amplifiers/Champion_600_schematic.pdf
as you can see, without those caps in the tone stack, (c 7,8, 9) there is nothing to block the dc b+. so you hit the pot with about 350 volts dc, which is wayyyyyyyyyyyyy above what it is designed to take.
use the .1 cap you have now to block dc. it should be able to handle the voltage. to see if it's the pot, jumper it right from the plate of the tube (pin 1 of the 12 ax7) right to where the output of the volume control goes... in this case, r14 and the amp should fire back up, minust any volume control of course.
if ya look at the schematic, the actual AC audio should be a bit less than 2vac .... you slammed that beotch with about 100x what it was designed to withstand.
check it out, and hollah back. i bet that pot is totally toast.
circled in red is the problems as described in my last post.
the brown squares are the stuff you can probably safely remove. i would consider leaving the 15k to ground there.
the green lines show where to connect what. notice the dc voltage is now blocked by the .1 cap, allowing the ac (audio) to flow thru unmolested.
you will def have to replace the volume control... any 1meg audio pot should do.
as you can see, you have about 1.7vac (audio) in the part of the circuit you messed with, and a dcv of around 310 or so after r 8 (100k)....
so ya blasted the pot with 300vdc or so. it could probably take it for a couple minutes... maybe.
but it would have popped. also check the continuity of the leads going between the pcb and the breakaway input board. something in there is fried. guaranteed. most likely the pot.
anyways... here's a graphic.
keep us posted.
again, PLEASE, keep ONE HAND IN YOUR BACK POCKET WHILE MESSING WITH THIS. 300 volts can do a lot more than tickle. :icon_eek:
(http://i605.photobucket.com/albums/tt137/pinkjimiphoton/New%20Bitmap%20Image_zpsncwcgwxl.jpg)
whenever dealing with audio, you HAVE TO BLOCK THE DC FROM PASSING FROM STAGE TO STAGE. there are indeed exceptions, but if you don't, in most cases you're gonna make yourself trouble. i forget the term for direct coupling two stages of a dual triode, but for all intents, that's what you did. handy for driving a marshall hard perhaps, but in this case the root of all your woes.
i really doubt the fuzzbox was anything more than coincidence. peace! :icon_cool:
How did you remove the tonestack because I know there is a mod out there that just involves lifting one resistor, leaving the rest of the circuitry intact. I believe it is R19. I've done this mod when I had a champion 600. It's always best to describe how you accomplished the mod, exactly what was done to the circuit instead of just a vague statement such as "I removed the tone stack" Which specific components were modified?
Quote from: davent on August 29, 2015, 11:04:31 AM
He's checked out the tubes and speakers...
Ah, must have missed that bit, my apologies. Carry on.
hey jimi...i definitely appreciate your concern for my safety and all of your comments about the whole thing. i promise i know enough about amps to not be poking around willy nilly and get electrocuted...i just meant i'm by no means an amp tech. also, i had forgotten exactly what i did to the amp but found a thread i'd posted about it. http://www.diystompboxes.com/smfforum/index.php?topic=109345.0
so i didn't completely bypass the tonestack, but put a big cap across C1. well, i used a switch and had the stock setting and then two bigger caps in parallel to c1 to get 3 different settings. i also ended up putting a bright cap on a switch.
my band played a show this past weekend and i've been busy with other stuff so i still haven't had a chance to mess with the amp, but i'm off the next two days and will do some investigating, but i did want to chime in and explain what it was i did to the amp. thanks to everyone for your comments thus far. if anything comes to mind i'm all ears. otherwise tomorrow i'll be reflowing my solder joints and taking voltage measurements.
sorry dan,
i just worry when i see peeps that aren't used to this much voltage. i've made plenty of mistakes myself, a couple that could or should have been lethal,
and i hate to see anybody get hurt, sorry if i came off like a dick.
rock on bro!
(http://i144.photobucket.com/albums/r170/cautionarycloud/Champion%20600%20voltage%20readings_zpsyxt5w5og.jpg) (http://s144.photobucket.com/user/cautionarycloud/media/Champion%20600%20voltage%20readings_zpsyxt5w5og.jpg.html)
don't worry about it man, you totally didn't come off like a dick. so i know it's been a month, but i finally got around to taking voltage readings. all of my actual readings are in RED above the schematic's voltages. the info at the bottom of the schematic says the readings have a 10% tolerance, and what i noticed is that i'm within tolerance on everything but the 3 voltages pertaining to the tubes. i'm getting too much on pins 3 and 8 of the preamp tube and too little on pin 8 of the 6v6. i do have a 12at7 in the preamp slot, not sure if that would affect things, but it was running fine for almost 10 months before it gave out.
i also measured the pot and it seems to be working just fine. nothing is obviously fried on the board...traces or components. both fuses are in tact. i reflowed the solder joints on the tube sockets and disconnected the mods i'd done. tubes still light up just fine but no signal is passing. does anyone have any ideas as far as what to look for next?
I *absolutely* can NOT read the drawing via PhotoBuck. Also it is complaining about my AdBlock.
How wrong (what numbers) are your wrong voltages?
> no signal is passing.
Touch the 6V6 grid with your voltmeter, head near speaker. This usually gives a small pop.
Touch V1b grid, should be a louder pop.
V1a grid, even louder pop (if tone/vol knobs not turned down).
If real-sure no pop from touching 6V6 grid, look for a dirty or cracked speaker jack (BTW, have you tried another speaker?).
A blown output transformer is *possible*, but exceedingly rare.
can't download a high enough rez to see the pic. try cropping it just to the schematic part itself.
here's the schem in pdf
http://support.fender.com/schematics/guitar_amplifiers/Champion_600_schematic.pdf
i downloaded the schematic, but i can't make heads or tails of the graphic you posted. i can see the red, barely, if i use irfanview to manify the heck out of it.
i doubt it's the ot. if it were, you'd be having other symptoms. first things first, change ALL the damn tubes. always. first thing ya do in a tube amp. always.
next, i wouldn't worry about discrepancies in voltage too much, you have as you said a 10% tolerance, if you're within the ball park, you should be good.
i would say audio probe time, something has broken down in the signal path itself.
take an old guitar cord and lop off one end. put a 630v (for safety's sake) cap on the hot lead on the lopped off end, solder some wire with a roach clip to the shielding.
wrap the whole mess in electrical tape except the free end of the capacitor.
plug something into the amp input that will be a continuous source of noise, music, whatever.. radio, cd player, some bud strumming an e chord or whatever....you need signal going in to the amp.
connect the roach clip to ground somewhere convenient, and use the free tip of the cap to carefully (yes, one hand in back pocket please) probe your way thru the circuit. there's not too much there. as you get closer to the power amp section of the audio path, expect to lose some volume. you don't have to touch any heater pins on any of the tubes... check the grid, then the plate, etc etc and each side of each cap in line with the audio. wherever you lose signal... and i still bet it's the volume pot... that's where your problem will be.
hollah back if any questions. i'm betting there's a bad trace (it happens... when sovtek first reissued the big muff pi, i blew the input traces on it by feeding my micromoog into it... literally melted the trace right off the board... called mike mathews at new sensor, asked him what it could be, and all he wanted to know was how it sounded before it blew up... i told him like the les paul of the gods)
it would be a lot easier too if you would write the voltages in the thread, cuz it's impossible to see them in the posted graphic. at least if ya type 'em out, we can look at the schematic to see what's what.
paul is giving you excellent adivice... if you hear pops at the grids of the 6v6, the amplifier section is ok. i'm betting you have an open cap or resistor that is not passing signal, which is also why the voltages look a little funny.
hang in there danny, i bet it's gonna be something stupid ;) that means easy to fix. ;)
take the free tip of the audio probe, and work your way into the circuit
sorry guys...thought clicking on the picture would open up in a new window. here's a close up:
(http://i144.photobucket.com/albums/r170/cautionarycloud/Champion_600_schematic-crop_zpsdpnrqufc.jpg) (http://s144.photobucket.com/user/cautionarycloud/media/Champion_600_schematic-crop_zpsdpnrqufc.jpg.html)
all of the voltages EXCEPT for the ones on the tubes are within tolerance.
as far as answering your questions:
the speaker jack is an open frame switchcraft style jack, which looks fine. i was running the amp into my deluxe reverb's speaker when this happened, and that speaker still works. i'd changed out the tubes right when it happened, but it made no difference so i put the original ones back in. i'll give the audio probe a shot as soon as i can, and i'll go ahead and swap the tubes when i do so. thanks so much for the guidance, guys. i'll report back with my findings. i'm tempted to open the thing up right now, but i'm exhausted and probably shouldn't be poking around the amp with only half of my mental capacity in tact haha.
> probably shouldn't be poking around the amp with only half of my mental capacity intact
++1 !!
When WELL rested, and amplifier OFF and well drained, use an ohm meter to measure the OT primary.
For some too-smart meters, the OT secondary may have to be loaded or shorted (damps the OT inductance which sometimes confounds a DMM's auto-ranging).
We expect a hundred Ohms more-or-less.
"Infinity" (open) is not good. Repeat your measurement. Look GOOD for bad joints (very popular). Then disconnect all leads and measure again. If the Plate-B+ winding is infinite Ohms, the OT is probably blown. The cheapest test is to find a scrap Epi Valve Jr OT on eBay (someone throws them out when upgrading Jrs) which will work in a Champ. (Not true Fender tone, maybe not every last part-Watt, but better than a dud OT). If the Jr OT works, then you decide to go Fender, you can re-flip the Jr OT, or save it for another adventure.
________________________
Theory: your tube voltages suggest low cathode current and high screen current. Is there any plate current happening?
34.6V across 1K R11 means 34.6mA here (screen current)
30.4V across 10K R12 means 3mA here (preamp current)
15.3V across 470r R10 means 32.4mA here (cathode current)
"ALL" the cathode current is screen current; NO plate current.
We are missing about 30mA-40mA of good plate current.
(There's a 1mA discrepancy which I will ignore as "tolerance and slop".)
The obvious culprits are bad joints, bad tube, bad OT. You did the tube. The OT is not cheap/simple. Re-re-check for bad joints.... it is really annoying to pay for iron PLUS shipping when what it wanted was a squeeze or a solder.
hey guys. i just probed the amp and i'm getting signal all the way through it up to T2. never having tested a transformer though, i'm wondering if you can chime in with tips/procedures.
also, thanks again for all the help. having this audio probe is kind of exciting. i'm sure it'll come in handy in the future.
Did you make the tests of the OT which I suggested?
oops, just did. i don't know why your suggestion sounded confusing to me last night. but yeah, i'm getting infinity on the primary. well, i guess that solves that, huh?
dammit, it would still be under warranty if i hadn't modded it haha. thanks again for the help, guys.
by the way, i'm finding transformers on ebay for relatively cheap. would a blues or pro junior transformer work? found one for $25 free shipping.
and a quick question about output transformers: the amp came with a 4ohm speaker, but does that mean that i HAVE to get a transformer that outputs 4ohms, or can i get an 8ohm output transformer and then swap my speaker? i'm figuring the output transformer is just receiving signal from the amp and that it solely is the reason the amp needs a 4ohm load, rather than the circuit itself being designed to be run at 4 ohms. does that make sense?
> would a blues or pro junior transformer work?
Someone check me, but I suspect these are Push-Pull (two 6V6) amplifiers.
Champ 600 is a Single Ended (one 6V6) amplifier. It needs a single-ended OT.
I think I mentioned that an Epi Valve Jr OT will work, and these often turn up cheap because people rip them out for other OTs. Sound won't be the same, but if money is a problem, I'd consider it.
the valve jr transformer was actually the first thing i looked for but i'm not finding any on ebay. it's looking like $50 for a new champ transformer. now that i know this is the problem though i can relax a bit and just wait for a used one to pop up :)
> it's looking like $50 for a new champ transformer.
That is obscene.
I see what you mean about eBay no longer bulging with Epi Jr tear-outs.
Here is a shop selling Champ OTs for around $30. I have not tried his transformers, but I have ordered small-stuff, he ships quick and charges only actual postage.
http://hoffmanamps.com/MyStore/catalog/partsenter.htm
Transformers
Heyboer Output for Tweed Champ
Output for Champ
Heyboer is an old-old transformer winder, made many of Fender's originals, and probably spot-on. The fact that it is $3 less than a "no name" (perhaps EH's subsidiary NS) is interesting.
8-Ohm outputs on Champish OTs are rare. Perhaps for historical reasons: Champ was a cheap amp, 4 Ohm speaker is a tenth-cent cheaper to wind, so they all come that way.
Weber VST is another (less speedy) source for amp parts. They changed the store pages and made it impossible to find anything. By shear luck I came across http://www.tedweber.com/w022905m which is a Champ OT with both 4 and 8 ohm taps, for $32.
Classic Tone has a couple SE Champ type OT's for reasonable money, they seem to get good reviews. Edcor is another to look at, though long lead times and Hammond has couple as well, 1750c &1760c.
dave
http://www.hammondmfg.com/guitarLineOT.htm
http://www.classictone.net/40-18030.html
http://www.classictone.net/40-18031.html
ordered a transformer from hoffman amps. cool site by the way.
so...i was thinking...now that we've discovered the problem here, can we discuss the possible reason(s) why this might have happened?
like i said in the first post, i was playing the amp full boar and hit it with a fuzz pedal, which made the amp cut out, come back sounding dark, then die. my tonestack mod was basically putting a .047 cap from pin 1 of the preamp tube to the R20/21 junction.
http://support.fender.com/schematics/guitar_amplifiers/Champion_600_schematic.pdf
the mod made the amp quite a bit louder, so could pushing it even further while running full up have just overloaded the OT? or was my mod just a bad idea in that it created a problem bound to happen (bad design)? i'm wondering because i really did like the way it sounded with the mod in place so i'd like to re-apply it when i get the new transformer if it wasn't the absolute cause of the failure. basically wondering if the stock OT might have been crap.
> .047 cap from pin 1 of the preamp tube to the R20/21 junction.
Lifting one end of R19 15K does the same thing, cheaper.
You SWEAR you never ran the amp without a load? That's THE way to kill an SE amp: no-load and full-blast.
> wondering if the stock OT might have been crap.
I don't see a lot of complaints about 600 OT failures. So I don't think it is made to fail. But it has a hard job and the least random defect could lead to failure.
speaker leads being abused, made to be loose intermittent connection might be a culprit, if i blew an ot, i'd go back from speaker any moving parts jacks crimp connectors. pcb's and traces are 'set', wires fail, crimps fail, jacks fail... this is why people immediately go to the ot. its the murphys law suspect. everything else is easy/cheap to fix. the ot is a pita and Over the Top time/money headache... point murphy... ;) bastid that he is...
i tried lifting one leg of r19 but it was so dull sounding. the cap mod ended up adding girth but retained some brightness...and to be honest i don't know the exact theory behind why, but it sounded a whole lot better to me so i went with it.
i promise i never ran it without a load. what i did do was run it into an 8ohm speaker when this happened...but i've heard a million times that a 2:1 mismatch is ok, and the amp says "4 ohm min" on it.
BUT.....something that you both (PRR and Quackzed) both hit on....so...no load. well, like i said, i didn't run it with no load, but i made this speaker extension cable a long time ago...like 12 years ago, before i had a "real" soldering iron and my soldering was just god awful....and i remember a few months ago i had a friend's blues deville plugged into my closed back cab so we could hear what it sounded like and while he was playing it cut out for a few seconds and i didn't know why. i wiggled my extension cable (male to female jacks) and it came back on. so that's probably why this happened. intermittent connection with that extension cable, which i had running between the champion 600 and an extension cab. so i guess that cable needs to go in the garbage.
as far as my mod though...the cap between pin 1 of the 12ax7 and the r20/21 junction...that's fine? cause damn, it sounded great like that haha.
SHE'S ALIIIIIIVE!!!!!!
Ordered my OT from Hoffman on Wednesday and it arrived today. SOOOO happy to have this thing working again. Even though it's such a simple/cheap amp I really did miss the tone of this little guy. Thanks so much for the help guys! I super appreciate it, and this taught me a lot.
now Replace that cable! ;) unless you got a 2 for 1 on transformers... ???