This was sent hours ago but was returned due to too many recipients.
----- Original Message -----
From: "Carl" <email@example.com>
To: "Scott McGrath" <firstname.lastname@example.org>; "Jim Tonne"
Cc: <>; "Vic K2VCO" <email@example.com>; "TMorton" <firstname.lastname@example.org>
Sent: Friday, October 03, 2008 11:10 AM
Subject: Re: [Amps] Transformer reliability? 34yr old Collins...
> Baking seldom gets down to the windings closest to the core on big
> transformers. Plus the oven doesnt like the weight.
> Ive cooked big ones by shorting the output and using a Variac and AC
> ampmeter on the input. Bring the voltage up slowly over a day or so to
> 75-80% of calculated or known primary rating and let it run a few
> days. A small fan can be used to move some air as well as heat a small
> room. Remove the end bells or an unsealed case if possible.
> If it now passes the megger test then remove the short and install a
> moderate load on the secondary and metering current and voltage. Bring
> up the variac while watching all 3 meters.
> Once your satisfied its time to varnish the beast and there are
> several options. Dip it while hot a few times, build a vacuum chamber
> or take to a motor shop. I used the shop on the big one as I didnt
> have anything big enough to put it in. A flea market pressure cooker
> works as a chamber, dont exceed around 15-20".
> Variations can be used on chokes and modulation iron as well.
> I cooked a 3500VAC 1.5A CCS 1946 built xfmr that failed the megger
> test for a week. Its been in regular use for over a month now.
> ----- Original Message -----
> From: "Scott McGrath" <email@example.com>
> To: "Jim Tonne" <firstname.lastname@example.org>
> Cc: <Amps@contesting.com>; "Vic K2VCO" <email@example.com>; "TMorton"
> Sent: Friday, October 03, 2008 9:33 AM
> Subject: Re: [Amps] Transformer reliability? 34yr old Collins...
>> You can bake it in a 175-200 degree oven for 6-12 hours and that will
>> dry it out. Do this while XYL is out. Barring that get a pound
>> two of silica gel from a craft store and place it and xfrmr in a
>> container for a couple of weeks in a warm place (top of furnace)
>> to mind
>> The bakeout is still the best bet though.
>> - Scott N1JIN
Amps mailing list