[Amps] Microwave Oven Autopsy

Dan_K9ZF n9rla at yahoo.com
Mon Mar 13 06:11:02 EST 2006


Tony,
How do you think a pair of the MOT's would hold up?  I've been planning 
to build a power supply like the one you put together, only using a pair 
of trannys in parallel.  This would be set up to drive a pair of GI7b's, 
hopefully....  Been in the planning stages for a couple of years now, hi hi.

73
Dan

Tony King - W4ZT wrote:
> I used a transformer almost identical to this one in my GS-35B tube 
> tester <http://tester.gs35b.com>.
>
> It has the welds nicely done connecting all the lams together. Even 
> after driving the shunts out the transformer is quite lossy. Even with 
> no load it gets quite warm when you apply primary voltage. I did drive 
> the magnetic shunts out. They were also paper wrapped and were fairly 
> easy to drive out.
>
> This transformer had one end of the secondary soldered to a lug that was 
> under a screw driven straight into a hole in the lams.  I took that 
> connection loose, slipped a short length of Teflon tube over the loose 
> wire and then soldered it to a solder lug that I put under the original 
> screw.  It put out 2200 VAC no load and with a full wave bridge produced 
> 3000 VDC with 56uF capacitance.  Unfortunately, the voltage dropped 
> quiet a lot under load. With 450 mA load, the output HV will drop to 
> about 2150 VDC.  Not a big deal for what I'm doing but not so good for 
> an amp.
>
> 73, Tony W4ZT
>
>
> wc6w at juno.com wrote:
>   
>> Hi Will,
>>    This one has four 1/8" wide welds down the opposing sides.  And yes, it has the shunts but, they are encased in transformer paper so, I'd guess that they could be easily driven out without disturbing anything else.  No screws what so ever.  The lams are even welded to the mounting frame in four spots.  The "cold" end of the secondary was soldered to a lug which was riveted to the lams -- I necessarily disconnected that wire for the hi-pot check.
>>
>>    It looks like it's wound at about 1 turn per volt.   As the core wouldn't practically dissassmble, the only easy rewind would be for a filament transformer.  The secondary could be sliced out by a careful guy and rewound with a bundle of large wires in parallel making a KW filament transformer... for say a 4CX5000/10000?   Or twenty 813's?  :-)
>>
>> 73 & Good afternoon,
>>   Marv WC6W
>>
>> **********************************
>>
>>
>> -- "Will Matney" <craxd1 at verizon.net> wrote:
>> Marv,
>>
>> Did you check to see if one of the windings was connected to the core, and if the core had a shunt in it? That is what most have that I've seen. Another thing that really ticks me about their manufacture, and a few other transformers too, is they weld the lams together. They put a weld right down one side of the lams, front to back, one bead about 1/4" wide. That makes them a bit*h to use for a rewind. A person with a mill, or be good with a disc grinder can remove the weld. Also, the shunt needs to be driven out with a hammer. This is really good though as it gives you more vertical window area for a new coil. What gets me though is why weld them and still use screws to hold the lams together?
>>
>> Best,
>>
>> Will
>>
>> *********** REPLY SEPARATOR  ***********
>>
>> On 3/12/06 at 11:57 PM wc6w at juno.com wrote:
>>
>>     
>>> QST
>>>  Yesterday, I acquired a 2004 vintage Sharp microwave oven, from the
>>> "alley exchange", which was light (weightwise) enough that I thought it
>>> might contain a switching power supply.
>>>
>>>  Upon examining the unit, I found that the incredible lightness was due
>>> to its construction with frame metal of soda can thickness, and that it
>>> contained a conventional transformer manufactured by one Digital Power
>>> Communications Co, Ltd.  
>>>
>>>  There was an article in QEX about 10 years ago that discussed the use of
>>> these microwave oven transformers in plate power supplies.  It advised
>>> against using them in a conventional full wave bridge but, rather used
>>> them in an unorthodox half wave connection.
>>>
>>>  Examining the transformer at hand, it appeared that the insulation was
>>> uniform over the full length of the secondary.
>>>
>>>  I disconnected the "low side" secondary lead from the frame and
>>> hi-potted the secondary (also the primary just for science...) up to 4KV,
>>> referenced to the frame, with zero leakage.  
>>>
>>>  This suggests that one of these transformers might be employed in a
>>> "normal" connection for a low voltage (2500V) KW input amplifier.   Or a
>>> pair of identical units in parallel for a 2KW input amp.   
>>>
>>>  Caution, this suggestion MAY NOT hold true for other makers of this
>>> style of transformer.  
>>>
>>> 73 & Good afternoon,
>>>   Marv WC6W  
>>>
>>>
>>> P.S. -- The magnets from the magnetron assembly make great refrigerator
>>> magnets!
>>>       
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>   


More information about the Amps mailing list