1952 Carvin amp - power transformer issues

[Resonator Guy]

Yesterday I got a 52 Carvin MOT lap steel amp. The seller, a thrift-type shop, said when he plugged it in there was smoke and a bad smell, so he immediately unplugged it. Stuff was dripping from the power supply (transformer). How true all of this is, I don't know, but it was cheap enough so my wife bought it for me.

I plan to test it by jumpering in new filter caps (the old can looks original and probably failed) put in a better but not real good 5Y3 plus 6V6 and 6SL7 and put it on a light bulb limiter. Then if that looks okay, plug it straight in.

Are there any terrible flaws in this, and if so, how does one test a power transformer. I don't want to replace it unless I really have to.
(no pictures because I signed in with IE not Chrome)

[Leo_Gnardo]

Yesterday I got a 52 Carvin MOT lap steel amp. The seller, a thrift-type shop, said when he plugged it in there was smoke and a bad smell, so he immediately unplugged it. Stuff was dripping from the power supply (transformer) Are there any terrible flaws in this, and if so, how does one test a power transformer. I don't want to replace it unless I really have to.

What's wrong, is your PT is pretty obviously fried. Now you COULD detach all the secondaries & try again. Sneak up the voltage with a lite bulb limiter if you want. Maybe outdoors where you won't stink up the house when it turns into a smoke machine again. I wouldn't think twice, just replace it. AND the filter caps. (I've just been thru the same, in an Ampeg Gemini II where the previous repairman replaced the PT with another fried PT. I put in one intended for a Vibrolux and it runs cool, although it takes up every millimeter of space available. Tight squeeze.)

[g1]

I'm agreeing with Leo that checking the PT with secondaries disconnected first is the best bet. If it gets hot fast, it's toast.
But I wanted to mention something about the filter caps. Jumpering new caps across is only worth trying if it's just a hum problem, where the caps are suspected of being "open", old and worn out, and not doing their job.
If there is any question of leakage or failure (smoke, caps running hot etc.) the original caps MUST be disconnected from the circuit or you will still have the leakage/short/low resistance in circuit.

[Resonator Guy]

Yep, by jumpering I meant attaching temporarily. The old ones would be disconnected.

[Resonator Guy]

Well, a busy afternoon peering into the rusty guts of this amp and then reading all I could find on various components has yielded some interesting stuff. First, the PT had far fewer secondaries than a champ trans, which led me to review the heater hookups. All were off one lead. The rectifier was so grubby no distinguishing marks could be found. I had simply, incorrectly, assumed it was a 5Y3. I searched close-up pics all over the web and now I believe it is (was) a 6X5GT, which doesn't read like a great tube for a guitar amp. A car radio, maybe. So, since the PT is shot and you cannot get a close replacement, I may get a Weber Champ OT with bell covers that allow vertical placement and rewire the whole thing to Champ specs. At least I will have something that works and for not a lot of bucks.
Another winter project. It is still a great birthday present even if it is just a wall hanger right now.

[olddawg]

One side of the heater string is grounded to the chassis which was frequently done back in the day. Are you sure the PT is bad? I have seen them take terrible abuse and still work. A short anywhere (filter cap, tube, etc ) could be making it get hot.

[Resonator Guy]

No, I am not sure yet, as I haven't been able to properly test it yet. I am going to unhook all the secondaries and plug it in to see what happens before anything else. It did leak something, hot wax maybe, but I have perfectly good ones that have dripped wax before. Any other tests that you can recommend?