[Amps] Transformer heating (problem?)

[David Craig]

    It may well have been Roger- I can't tell for sure.  One thing that 
bothered me a LOT was that when redoing the E I core lamination thru bolts, 
some of the plates were not aligned properly- I had to grind/drill parts of 
the holes to get a teflon-insulated bolt thru it (and it was markedly 
smaller than the actual core hole diameter).  This is beginning to appear 
more & more like a bad transformer design/assembly issue.  73 Dave


----- Original Message ----- 
From: "Roger" <sub1 at rogerhalstead.com>
To: <Gary at doctorgary.net>
Cc: <Amps at contesting.com>
Sent: Thursday, February 12, 2009 1:38 AM
Subject: Re: [Amps] Transformer heating (problem?)


>
>
> Gary Smith wrote:
>> I'm sure no expert, any chance the Iron's not built for 60Hz?
>>
>> Gary KA1J
>>
>>
> My question would be: has the transformer ever been fully disassembled?
> To me the original problem would have indicated this might be a strong
> possibility.    I'm assuming this is the standard "E" frame with the
> laminations interleaved.  If so it's possible the laminations may have
> been cleaned leaving them to make irregular contact with each other,
> causing some current loops, or aggravated historesis (sp?) loss.
>
> It's been over 40 years since I studied this stuff so I may be wrong.
>
> 73
>
> Roger (K8RI)
>>>     Corollary to a previous issue with a B+ transformer I passed thru 
>>> the group a while back, which before I repaired it had a current loop 
>>> due to bad/no insulation on the core bolts.  Transformer has a 240V 
>>> primary, 2800-3000V secondary rated at 2 amp CCS.  Is installed & in use 
>>> on a HB GS35b 6m amp.  When "module" testing the amp the transformer 
>>> taps met specs, measured with a Simpson 260.  Calculations based on 
>>> measurements then indicated a 12.5 to 1 ratio.
>>>     Fast-forward to completed amp...After some occassional use (~30 
>>> minutes of total operating time) am having the following "issues."  The 
>>> 3000VAC secondary tap is now only putting out 2700VAC with line voltage 
>>> measured at 243VAC  (240V mains line is 10 guage wire, a 10 ft run from 
>>> the breaker box & then 6 feet of 12 guage line to the amp...  original 
>>> measurement taken with same lines).   The even more disconcerting 
>>> problem is that after a couple hours of sitting at "idle" (amp on, power 
>>> to B+ but no RF) the transformer iron is getting hot- enough that you 
>>> wouldn't want to keep your hand on it for long, and particularly so near 
>>> the left & right sides of the core. (Yes, I checked the plate meter & no 
>>> current thru tube, bias relay fine).
>>>      Lamination bolts remain cold so no more current loop around the 
>>> mounting brackets....   I am baffled as to why this thing is getting hot 
>>> just idling.  There is no "bleeder" per se on the PS, just 6 x 220k ohm 
>>> Rs across each of twelve 450V caps in series.  The only other constant 
>>> current draw is a 5 MEG dropping R to the B+ meter.  I am baffled as to 
>>> why the transformer laminations would get hot with almost no current 
>>> draw, and am concerned that once I really work this thing out during a 
>>> contest or Es opening the heat is going to short the secondaries.
>>>     Any ideas as to what could be going on?  Is this normal, or as I am 
>>> beginning to think, an 86 lb misdesigned piece of junk??? Any input 
>>> appreciated.
>>>
>>>     73 Dave N3DB
>>>
>>
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