i blew my amp up. can you help?

[PRR]

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.

[pinkjimiphoton]

can't download a high enough rez to see the pic. try cropping it just to the schematic part itself.

[pinkjimiphoton]

here's the schem in pdf

http://support.fender.com/schematics/guitar_amplifiers/Champion_600_schematic.pdf

[pinkjimiphoton]

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

[ode2no1]

sorry guys...thought clicking on the picture would open up in a new window. here's a close up:




all of the voltages EXCEPT for the ones on the tubes are within tolerance.

[ode2no1]

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.

[PRR]

> 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.

[ode2no1]

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.

[PRR]

Did you make the tests of the OT which I suggested?

[ode2no1]

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.

[ode2no1]

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?

[PRR]

> 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.

[ode2no1]

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

[PRR]

> 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.

[davent]

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

[ode2no1]

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.

[PRR]

> .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.

[Quackzed]

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...

[ode2no1]

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.

[ode2no1]

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.