Champ problem

[yodaeatsfishstx]

I built myself a Champ clone during the fall, it worked right away, sounded great, I was pumped.

After doing so reading on them, I found out that the Sovtek 5y3 rectifiers put out a little more voltage than they ought to. So, thinking I'd be making an upgrade, ordered a NOS Phillips 5y3 to throw in there....

I installed the Phillips, turned the amp on, and got a little hum and some glow from the tubes, and then...SMOKE! Coming from a pair of resistors attached to the bulb. I quickly shut it off, it had only been on for a minute or so.

OK, so, all I changed was the rectifier, maybe it was just a bad tube. I put the Sovtek back in, THAT HAD BEEN WORKING BEFORE, JUST FINE. I got a HUGE amount of hum, the Sovtek began to glow white, spark and looked like it was about to explode.

So I said to myself "Self, the only way that could happen, is theres just too many electrons coming from the transformer, everything that tranny touches directly ( the resistors on the bulb and the rectifier) gets wrecked. Upon testing the transformer, all the leads put out the right about, EXCEPT THE RED LEADS THAT GO TO THE RECTIFIER. They're supposed to be putting aout 650 V CT and they're putting out 760!

Long story short (too late) why would this have happened?

[TweeDLX]

Voltage will be higher without a load (tubes). I'm guessing the NOS tube was bad and took some stuff down with it. Are all the resistors that smoked replaced? The ones you described sound like the heater center taps. Replace them, then test all related component values. Replace any that are off spec.

[Jerry Glass]

Sounds to me like your 6V6 shorted, cathode to filament, and took out the two resistors on the bulb assembly. It could be that the NOS 5Y3 was bad or it could be that this was a 6V6 failure waiting to happen and by disturbing the circuit with a new tube you aggravated it.

If the rectifier behaves the same with the 6V6 removed, you may have a shorted filter cap too.

[yodaeatsfishstx]

all of the events i described happened with as well as without the 6v6 installed

everything worked fine for the fall, it sat unused for the winter, then i put in that phillips and all this started. so i don't think it could be a short, nothing about the wiring changed at all.

when a resistor dies, will current still flow through it? or does it just lose its resistance?

i also noticed that most 5f1 schematics do not have the two 100 ohm resistors (the ones that burned out) on the bulb at all

[TweeDLX]

They protect the heater circuit. Better to lose two small resistors than the entire amp.

[TweeDLX]

Depending on how they fail, resistors can change in value, or simply short out.

[Jerry Glass]

Sounds like a filter cap failure. If this was a kit, where did it come from?

[yodaeatsfishstx]

Mojotone, which I believe gets their kits from Marsh.

HOWEVER the tubes trannys and speaker were all purchased seperately.

where exactly is the filter cap? and why would it have worked before ?

[TweeDLX]

Filter caps are the big cylindrical objects at the end of the board by the PT. Should be 3 of them. 16uf, 8uf, and 8uf. If you have a drastic part failure (you did), it can sometimes take other parts with them.

[phsyconoodler]

Quote:"Mojotone, which I believe gets their kits from Marsh."

Other way around.Mojo supplies kits to Marsh.

You have some issues that sure sound unrelated to the rectifier tube.A rectifier tube will not short out a heater winding like that.More likely the 6V6 and maybe some haphazard wiring on your part.If you don't know where the filter caps are,it's a wonder you didn't kill yourself assembling this amp.
Where is the fuse in all this shorting and sparking?It should have blown instantly.That is unless it's the wrong value.Should be a 1 amp slow blow fuse.

[Prattacaster]

If you don't know where the filter caps are,it's a wonder you didn't kill yourself assembling this amp.

+10 to that, be careful, bud, that's insane that you built a working amp with out knowing what a filter cap is. I dont know whether to be proud of you or figure out where you live so i can run the other direction.

[TweeDLX]

Some photos of the guts would be helpful here...especially the burnt parts.

[yodaeatsfishstx]

i know what a cap is, i know that they are dangerous. i know not to touch them. i should've asked "which filter cap would it seem would cause this" or "where is the filter cap in question"

AGAIN, this amp worked FOR MONTHS, just fine, until i put in that phillips tube. i've ordered a new transformer as this one is running WAY above spec. don't know why, but it is. the problems i'm getting with the rectifier are WITHOUT THE 6V6 INSTALLED as well as WITH.

also, when i called mojo, they told to contact marsh, telling me that is where they get them from.

[TweeDLX]

Have you checked any caps or resistors for damage, drifting, DC leakage yet?

[Prattacaster]

[QUOTE] know what a cap is, i know that they are dangerous. i know not to touch them. i should've asked "which filter cap would it seem would cause this" or "where is the filter cap in question"
Yea, I think we've all been victims at one point from "lack of clarity". I really didn't think there was a way you could go thru the process of building an amp and not know what filter cap were, anyway..
In my short tenure here i've learned to heed what Jerry Glass says, not to mention I've worked on an amp that has those exact symptoms and it ended up being the filter caps. A bad filter cap can make the recto do funny things, like self-destruct. I could be something else but I would look into those caps first.