Hi Russ, You speak the truth...
I still have an old Speedy Memo somewhere in my shack library from one of the Hammond Transformer engineers in Guelph, Ontario, Canada, advising me to literally BAKE any long-unused, vintage, unpotted transformers in the oven, to remove residual accumulated moisture BEFORE using them! (or pay the consequences, Hi Hi). If memory serves me well, I believe they should be "cooked" upside down, at about 200 F, for a couple of hours... It certainly makes sense to me. What I do here to the "end bell" types with "open" bottoms is pump the insides up clear level with the bottom of the bells with clear silicone sealant after they've dried. I smooth the sealant flat at the bottom, so the thing will rest properly on the chassis. I figure this extra bit of work "seals" the windings, and discorages any undo tendency to vibrate, as well... I've done this to about 4 transformers, or so, & have yet to experience any failure (TOUCH WOOD, Hi Hi). ~73~ Eddy VE3CUI - VE3XZ> It is not really unusual for these transformers to go bad. You > must consider the age and how they were manufactured. You can > blame Johnson for using cheaper transformers, they could have > used potted designs. But who would have thought that you would > be using this old stuff? Old transformers do bad things- they > suck up moisture in the air and the windings viberate and break > down the > insulation. I don't think you will find anything seriously wrong > with your amp. Heres an experiment: got an old unsealed > transformer in the basement that has not been run in a few years? > Put it in the oven@ 200 degrees. Just leave it in for a few > minutes. Open the oven door and you are likely to see it > steaming! > Thats water.....Russ. > > > > > > >>From: Dave Aabye <[EMAIL PROTECTED]> >>Reply-To: [email protected] >>To: [email protected] >>Subject: [AMRadio] Re: 500 Transformer >>Date: Mon, 10 Feb 2003 14:20:22 -0500 >> >>Hi Gary, >> >>Yep, it's a bummer! >> >>WZ1M wants $260 to rewind the existing transformer. Peter Dahl sells a >> replacement >>for $285. I think that Dahl offers a better deal because it is a >>hypersil unit >>with a 500 ma CCS rating. I believe the original is rated 400 ma ICAS. >> Only >>drawback is the need for 4 new mounting holes. >> >>I replaced the tube recitifiers with solid state units shortly after >>purchasing the >>500 (about two years ago). I also inserted thyristers in the primary >>leads to cut >>down on inrush current. I wonder if you have any further protective >>measures to >>suggest. >> >>73 de Dave, W4QCU >>Oak Ridge, TN >> >>Gary Blau wrote: >> >> > Dave: >> > >> > Ouch. Sorry to hear that. >> > Sounds like WZ1M's offer to rewind might be attractive, unless you >> > can find another 500 xfmr somewhere (good luck!). That's a great >> > rig so it's worth the investment. >> > >> > Now, to find out why it went bad in the first place... >> > Best of luck. >> > >> > Gary >> > W3AM >> > >> > Dave Aabye wrote: >> > > >> > > Hello Gary, >> > > >> > > Thanks for the suggestion, which I believe has proven to be >>conclusive. >> > > >> > > I hooked my Variac to the primary and slowly increased the >> > > secondary >>voltage. >> > > The caps were disconnect from the rectifiers, so the transformer >> > > was >>"all by >> > > itself". At about 700 volts, the voltage started to jump just a >> > > bit. >>At >> > > maybe 750 v, the secondary emitted a puff of smoke with an >>accompanying hiss. >> > > >> > > I think it is clear that the transformer is shot. Time to call >> > > Peter >>Dahl! >> > > >> > > Again, thanks for your input. >> > > >> > > 73 de Dave >> > >> > _______________________________________________ >> > AMRadio mailing list >> > [email protected] >> > http://mailman.qth.net/mailman/listinfo/amradio >> >>_______________________________________________ >>AMRadio mailing list >>[email protected] >>http://mailman.qth.net/mailman/listinfo/amradio > > > _________________________________________________________________ > STOP MORE SPAM with the new MSN 8 and get 2 months FREE* > http://join.msn.com/?page=features/junkmail > > _______________________________________________ > AMRadio mailing list > [email protected] > http://mailman.qth.net/mailman/listinfo/amradio
