Burned out OT? Challenger CC30

[angelodp]

Hi, I have a Challenger CC30 amp that I am bringing up. I have begun to convert to a guitar amp. I have a typical input 1M and 68k and changed out V2 to a 2.2k/10uf Cathode setup. I have a three prong plug, fuse and switch. Death cap and service two prong plug are eliminated. I have swapped a few of the Electrolytic caps including the 6L6 cathode cap. I did bring the amp up on a limiter (no Tubes) with variac and while I have a dim glow I do not see any shorts. I put in a Rectifier and again no shorts.

Before I go much further, I checked out the OT and as I read from the CT of primary (B+) to either side of the primary windings I get 150ohms on one side and 4.1k on the other. According to Geofex I do believe I have a burned out OT? Yes?

Thanks Ange

[angelodp]

I have a Dagnal 2507 on hand that might just do the trick.

[Phil_S]

...I get 150ohms on one side and 4.1k on the other....

No longer good for what you want, but it might be OK for single ended use with a low power tube. One of the big differences between PP and SE is that SE OT has an air gap in the lams to manage saturation. Mostly, though, it's a paper weight or a door stop.

If you have spare time, you might enjoy breaking it down. You'll get an appreciation for how to build an OT and then you won't ever want to do it. First, there are a couple of clips that need to be extracted. Then, split off the lams one at a time using a razor knife to break the varnish. Keep them stacked in order -- you may want to reassemble. Once you get the core free from the lams, you can see what you want to do with it. There is a remote possibility that one of the leads isn't quite right and you might be able to replace it or there's a problem in the outer layer that you can just snip out and repair. If this turns out to be the case, having the lams stacked in order will allow you to reassemble the OT. You can get appropriate high temp rattle can varnish. Spray and bake when you're the only one home, or better, bake it in a propane grill outside. Allow at least several days to get a project like this done. You can't keep at it all day and braking out the lams is a tedious thing to do.

Well, just my 2¢. Sorry for your loss.

[Stevem]

The 150 ohms on one primary leg sounds normal, the 4K does not, but is far from a short!

I will bet that normal high V+ voltage that you see on the 150 leg does not show up on the 4K leg.

[angelodp]

Thanks for the replies. You actually think this can be used in a SE amp? Here's the pic of the burn out that I was not seeing when it was in the chassis. I doubt this can be repaired.

I do have a few possible replacements.

[angelodp]

BTW here is the amp as of this point. My plan is to have a listen with the amp, and then move onto a Fender Pro.

[sluckey]

I would put it in the trash can.

[angelodp]

Oh goodness, no redeeming value here? I respect and and admire you Steve. I like to tinker, so, I will press on

Oh, you meant the Transformer.... Yes in the garbage.

[Phil_S]

Missing your opportunity to take one apart without fear?

[bepone]

Thanks for the replies. You actually think this can be used in a SE amp? Here's the pic of the burn out that I was not seeing when it was in the chassis. I doubt this can be repaired.

I do have a few possible replacements.

this is not possible to repair. laminations are possible to recover and with new bobbin , new OT can be wound

[angelodp]

Phil, yup I have torn a few apart to have a look. I guess some folks around here actually make their own T''s - Then there is the guy in Europe who makes his own tubes - egads.

Anyway I did manage to find the elusive CC30 Challenger schematic.... which is is more or less the Bogen CH30.... Thanks to a dear friend Steve G.

I actually have an OT from Colossal that has been sitting in a box for too many years..

[trobbins]

I'm guessing you don't know the history of that amp, so it may be worthwhile thinking about what caused the OT primary to burn up, as there may still be a problem with parts/sockets, and you may want to think about avoiding a similar fate with any rebuild.

Can you tell if the 200R common cathode resistor, or the 100R B+ feed resistor, have been overheated? Can you test if the 0.1uF coupling caps are leaky?

One possibility is a coupling cap went leaky and one 6L6 conducted full-on, and the available continuous current was sufficient to cook the nominal 150 ohm DCR winding (whose resistance would increase with cooking temperature). The nominal idle winding current would have been 0.5x24/200 = 60mA, so 0.54W. Even with screen voltage sag, the 6L6 may have been able to conduct above 150mA which would cause circa 3.4W dissipation or more.

Another possibility is a heater to ground short, which could also have pushed both 6L6 in to full conduction - and maybe only one 6L6 had enough cathode emission to support a high anode current.

Another possibility is 6L6 anode to heater carbon tracking on the 6L6 socket, but that's a bit more complex to deduce an OPT failure from.

And of course there is also the possibility of OT windings corroding/touching and causing shorted turns.

[angelodp]

Thanks for the heads up, I will go through all these points before proceeding.

Best A