I let the magic smoke out of my fender champion 600

[nomadh]

Yup. I lifted the tone and neg feedback circuits. I really liked the tone but I guess the amp didn't. IT ran fine for a day until I went to max vol. Sparks , arcing in the tube and smoke. I think the stock tube couldn't handle it but I'm open to better theories. This was my first mod so I'm off to a smokin start. Anyway I need a new xformer and I'm hoping to keep the price down. I'd like to have something a step up from oem specially if it has multiple speaker impedance taps. I read that the original was11k ohms but I see lots of mention about using 8k and even some 5k. Are the specs really that loose? I see a 40-18030 and a higher power 031. Also T08c or 11c hayboer at double the price. None of these are at 11k from what I can tell. What do you guys suggest and why? I mostly want to get some experience and get this thin running again and reliable. Maybe a step up if reasonable.
Thanks for any help.

[MWJB]

No Champ output transformer was 11K as far as I know, 5-8K are more typical. Impedance is fairly flexible, so long as you stick within a safe margin (4K-16K?), specific impedance is chosen as a matter of taste. Any tweed or tolex style Champ OT will do.

You are sure that it is the transformer that went? I'd also be looking to use a 5W cathode resistor for the 6V6 & a 50v min rated bypas cap, especially if you like to play the amp dimed a lot.

Lifting the tone & NFB circuits specifically should not have caused this, triple check that you have not disturbed anything else.

[nomadh]

This is the new champion 600. I don't think its the same as the classic champ very much. I saw that someone did a test and came up with 11k. So if I do go with 5 or 8k is there any rule of thumb as to why I would pick one or the other? I thought if I changed the input impedance that would mess with the reflected formula causing the calculated speaker out ohms to need to be recalculated.
The transformer now reads just <1 ohms on the speaker side coil and 260 ohms on the tube side. I also found 4.3k ohms between the coils. Shouldn't that be an open? Also I do want to beef up a few components.
Didn't modding the circuit like i did allow much more power to go through the output section? I felt like a full 5 watts after the mods before it blew. I'd guess it ran at < 1 watt output as stock. Similar to my friends. Very tame and quiet.
Also is there a dvm test I can do on the 6v6 just to see if its functional or at least if it will short something if I try it. I'm pretty sure I saw sparking inside the tube.
These are notes from a few months ago when I blew it so I will check some of these again and look for more possible problems.

[jrfrond]

An arcing tube would have cooked the cathode resistor. That's what happened with most of these amps when they failed prematurely.

[MWJB]

"I don't think its the same as the classic champ very much." Yes it is, it's almost the same as a BF Champ, just with fixed tone controls & schematic voltages (genuine BF champs all read higher than the schem. The voltages are more in line with a 50's Champ...that's why either a tweed or tolex Champ will do, asfar as the OT is concerned, it Is pretty much the same...even if it has little in common with the two tone vintage Champion, with which it shares very few components indeed.

"I saw that someone did a test and came up with 11k. So if I do go with 5 or 8k is there any rule of thumb as to why I would pick one or the other? I thought if I changed the input impedance that would mess with the reflected formula causing the calculated speaker out ohms to need to be recalculated." Primary Z, as long as it does not cause premature failure, is chosen for tone, Fender have pretty much "tested" this with millions of Champs in the last 60yrs, a typical tolex Champ OT might be around 7K nominal...close enough to 5K or 8K, fretting over a few hundred ohms is pointless, as when you start to play impedances will change with frequency response, at 3.5KHz it might be twice the nominal rating.

"The transformer now reads just <1 ohms on the speaker side coil and 260 ohms on the tube side. I also found 4.3k ohms between the coils. Shouldn't that be an open?" The first 2 measurements sound ball park...never tried to measure between the windings, so can't say on that one. Remember impedances are AC & you are measuring dc resistance.

[nomadh]

So how do I prove what componets are bad? I sure hope I dont have to have scopes, sig gens, and tube testers just to get this little amp back on the road. All I have is a dvm. I've been googleing all this but I have not found much.
I will also check again for a burnt resistor
Thanks.

[nomadh]

Here is the link that gave the 11k. But of course its a moving target with 14k at 1khz and I forgot it was 8k at 100hz.
Is there some std for what freq a transformer impedance is measured?

akavalve: Fender Champion 600 Output Transformer

[MWJB]

"So how do I prove what componets are bad? I sure hope I dont have to have scopes, sig gens, and tube testers just to get this little amp back on the road. All I have is a dvm." As far as we know your problem is simple, your amp does not work, so far we just need it to function...you do not & never will need a scope & a signal generator to take this step, a DVM is fine.

John F has already pointed you towards the 6V6 cathode resistor, with the amp unplugged from the wall, measure the ohms from pin 8 to of the 6V6 to ground, or the accross 470ohm cathode resistor (R10) connected to it, to ground. It should read 470ohms, if it reads a short then the cap that bypasses it (C4) may be shot, if it reads open then the resistor may have burned up (this may leave visible signs). Anything odd at all replace R10 with a 5W 470ohm resistor, replace C4 with a 25uf 50v (or better) cap. Fit a new 6V6 (you have great "tube tester" already, the amp itself)...power up...what happens?

Forget the OT primary Z, you have a champion 600, use a champion 600 OT, or any other champ OTwill do (the article in the link is wrong, Champion 600s do not run higher voltages than old Champs) "IF" you actually need one - replace the tube first & check components mentioned.

[nomadh]

Still need to get time to dig into the amp again but I saw this troubleshooting idea for the transformer. Thought I'd throw it into this thread. I see that my xformer may actually be ok from memory.

Noting which leads connect to the B+ line, measure the resistance from the B+ leads to each plate of the output tube(s). Write the resistance reading down. Measure the other side if it's push pull. Plate windings are almost always in the tens to a few hundred ohms of resistance. A reading much over 1K is pretty sure sign that the winding is burned open. If it's open, the transformer is dead. While you're at it, measure the resistance of every lead to the housing. This reading should be very high, hundreds of K or preferably megohms. A low reading here indicates a short to the transformer core - again, dead transformer.
Do similar tests on the secondary’s - look for open windings, or shorts to the core. Finally, test for the resistance from primary to secondary. A low value, under a few K indicates an internal short, and a dead transformer.
If the transformer fails any of the simple tests, it's dead. Replace it. If it passes all of the simple tests, it may still have an internal short Sometimes a primary will have enough resistance that the transformer does not burn up or burn the wires in two , but will just bog down, have low power and sound bad. If you suspect that is the case and you don't have the skills to do the advanced tests, take it to a competent tech.

[Jag]

Like MWJB said,

John F has already pointed you towards the 6V6 cathode resistor, with the amp unplugged from the wall, measure the ohms from pin 8 to of the 6V6 to ground, or the accross 470ohm cathode resistor (R10) connected to it, to ground. It should read 470ohms, if it reads a short then the cap that bypasses it (C4) may be shot, if it reads open then the resistor may have burned up (this may leave visible signs). Anything odd at all replace R10 with a 5W 470ohm resistor, replace C4 with a 25uf 50v (or better) cap. Fit a new 6V6 (you have great "tube tester" already, the amp itself)...power up...what happens?

Why not check this first? John didn't make this suggestion for no reason!

[nomadh]

Yup. ASAP. Wish I could have a few days ago. I'll let you know what I find.

[nomadh]

R10 checks out at 469 ohms.
I tested the output xformer and I got .8 and 264 ohm
the .8 winding (yellow and black) also measure <1 ohm to the metal frame of the xformer
I thought I had a measurable resistance between the 2 coils but I'm finding that as an open now.
So it looks like the one winding shorted to the core or the frame of the transformer. It that correct?
I want to trouble shoot this fairly deep before I plug anything in. I currently don't even have a spare 6v6. I do have a 6L6 if that will help test but I dont want to risk it either.

Also I tested from every pin of the 6v6 socket to ground and they were all infinite. That was with the O.T. and the tube out of the circuit. I need to do a lookup to see the pin numbers again. What should it be from pin 8 to ground?

Also I dont see anything burned. I didnt remove the pcb but the underside looks fine. There is some talc type residue here and there but it looks like it was from mfg process. Its a pale grey and rubs off easily. Maybe it was smoke residue when it was smoking. It doesnt look like its from any particular component.

So other tests ? Any way to test the tube with my meter at least partially?
Time to order the OT?

[nomadh]

If I do need an OT I saw these at musicalpowersupplies.com at $19 and 23.50 . I think thats the best prices I saw so far. If I step up to the bigger model is it true that might let me run a 6l6 if I ever wanted too. Its an interesting option but I'd be worried that it might give me either more power(louder) or cleaner at the low vol 6v6. I do plan on using it as a quieter balls out amp. I already have a 30 w and a50 watter tube amp. But if the bigger iron let me run the 6l6 it might be a fun side project.
Thanks for any help.

OT8SE

5W to 8W SE Guitar Amp Output XFMR
82Hz to 10KHz, 45mADC
7000 Ohm and 5000 Ohm inputs to 3.2/8/16Ohm Outputs.

Circuits: Champ, Bronco, VibroChamp, Valve Jr etc using a single EL84 or 6V6 Power Tube

Competitive Xfmrs:
Fender125A35A/022905
Hammond 1750C, P-T125BSE


$18.95 Direct
$18.50 @4pcs
$18.00at 8pcs
OEM- EMail for price

BUY
OT10SE

8W to 12W SE Guitar Amp Output XFMR
82Hz to 10KHz, 60mADC
7000 Ohm and 5000 Ohm inputs to 4/8/16Ohm Outputs

Circuits: DIY Upgraded Champ and Valve Jr using 6L6, 5881, KT66 Power Tube

Competitive Xfmrs:
Hammond P-T125CSE, P-T125DSE
Edcor XSE10



$23.50

BUY
Direct
$23.00 @4pcs
$22.50at 8pcs
OEM- EMail for price

[MWJB]

264 ohms accross the primary sounds ball park, as does 0.8 ohms accross the secondary - these figures alone do not indicate a problem. The secondary (0.8ohms) should be grounded via the speaker jack (or similar), it may also have an internal ground connection that you cannot see.

6V6 are cheap, get this first...even if your OT is shorted it will just change the current & voltage that the tube sees, probably not enough to kill it.

"Also I tested from every pin of the 6v6 socket to ground and they were all infinite." you just told us that R10 checked out at 469ohms, so how could pin 8 to ground read infinite?

The OT alone does not dictate whether you can run a 6L6, you need to have enough current suply on the heater & B+ winding. You already have a solid state rectifier (no obvious way to increase B+), so your power will not rise with a 6L6 anyway because secondary voltages will drop.

You seem to have tunnel vision with regards to buying an OT, so buy the prettiest, or the most expensive one ;-)...you're obviously not that concerned about the values or what is stopping the amp from working otherwise you would be checking the more obvious things first.

[nomadh]

No, I'm actually pretty cheap. It would be cool if it wasn't burnt out. Just when you see smoke you start making assumptions. I thought the secondary to ground proved a short. I see what you mean there with the sec going to ground. I took the xformer out of the circuit and there is no short. I swear I did actually used to be decent at this back in electronics but I'm so rusty now and we never learned diddly about tubes. I even asked back then and the instructors had quite the laugh over it.
I checked pin 8 again. I probably just had a bad connection to the meter probe but I do see its 470 now.
I've been waiting on getting the new 6v6 because I have not really proven it was bad either. Do the sparks inside prove its bad but a smoking xformer is still ok? Once I figure the best guess as to what I need I may just buy it all at once.
Sorry I keep jumping the gun but mistakes are the best way to learn, specially as I'm keeping this online. Maybe in the future dozens of other people will read this and know what to not do
What do you suggest next? Anything else to test or just try a new tube? I see test voltages on the schematic but I think those only apply with a new tube installed in a running circuit?
Thanks for the help MWJB, I couldn't even begin without your pointers.