Okay, I was wrong! - Printable Version
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+--- Thread: Okay, I was wrong! (/showthread.php?tid=1922)
Okay, I was wrong! - Music in a bottle - 07-20-2009
After extensive lab work incorporating a stethoscope, I determined that there indeed was a mechanical thump, and sound, and that it is the power transformer in the right module, and not the power caps! The other caps I put in mus have altered the in rush of current, giving me different charactaristics, than I had with the original set. When you put a finger on the tranny, you can feel the bump at power up. I have 3 parts modules and I better get a soldering iron I guess. Thank you for the advice guys and sorry I gave bad info and had you all over the place.
Re: Okay, I was wrong! - kruc - 07-21-2009
You should still replace those old electrolytics that are as old as you are.
Dave
Re: Okay, I was wrong! - Music in a bottle - 07-22-2009
kruc Wrote:You should still replace those old electrolytics that are as old as you are.Come on Dave, I'm not that old!
Dave
Okay, I'm replacing them!
Re: Okay, I was wrong! - kruc - 07-22-2009
In the book Old Time Radios by Joseph J Carr the author writes that some stethescopes have conductive tubing to be able to be used in an explosive environment. He cautions that the tubing could be a path from B+ directly into your head. Better meter it out before you get a rude surprise.
Dave
Re: Okay, I was wrong! - Music in a bottle - 07-23-2009
Surprisingly, I thought about that and used a piece of cloth as a buffer! All the leads have the correct voltage according to the schematic. Unsure why that transformer is thumping mechanically and the other isn't. Loose core? I have a nice scope, and would check the AC waveform coming from the transformer leads, but what would that show? Anything?
Re: Okay, I was wrong! - codefox1 - 07-24-2009
Okay, agree with eveyone. There is another reason for mechanical thumping of transformers. If the transformer was selaed in wax withing the bells, and ever overheated due to operational stess or being stored in a very hot place like an attic in the summertime, some or all of the wax might have melted and dripped away. Often you can find artivacts of this as lumps of wax on the chassis, or if long enough ago, rust spots. So if the windings are slipping on the core, you could easily hear a thump or buzz when the set is turned on. I have seen articles where people have soaked old transformers in varnish and baked them in ovens, and on and on. I have one nice amp which exhibits this same behavour, but otherwise plays just fine. On the other hand, I have seen cases where the filter caps are going bad, not enough to blow the fuse, if in fact the set has one, or to blow the rectifier, be it a tube or solid state, or a bad coupling cap in the output stage, but a pig on power nonetheless. This would be accompanied by the hot tranny syndrome, and confined to the narrow definition of radio diagnostics, being a symptom worth investigating. I have rescued quite a few transformers that had arcing connections, starved and overheated windings, excessive ringing and thumps. God help me, but I have secured loose ones with a liberal glob of Elmer's Glue left to dry for at least a week atop the furnace before returning to the bells. Works.
Re: Okay, I was wrong! - Music in a bottle - 07-24-2009
I'm going in! Will report my findings.