[Amps] An inexpensive choke for a resonant filter

Thu May 17 04:13:43 EDT 2007


Thank you for this very useful information.

Maybe the primary of a microwave oven could be wired in series with the 
secondary (forward or backwards, depending on the  inductance you want)  
and be used to "fine tune" the total inductance by adding or removing 
some turns.

Has any other group member experimented with microwave oven transformers 
used as chokes?

Also, I wonder how much protection against overcurrent at resonance can 
be expected from the magnetic shunts of the microwave oven transformers?

Can it be said that the magnetic shunts would lower the Q of the 
resonant filter?

And that they would do so without dissipating any heat?

Lowering the Q of the resonant choke would be a good thing in terms of 
safety. On the other hand, this would probably reduce 120 Hz ripple 

Any ideas?

Vy 73 de Angel HB9SLV

Radio WC6W a écrit :

>   Here are some real numbers for simulation:
>      A 3KW Varian plate transformer (85 lbs)
>            240V Primary --  2.2 ohms DCR,  40 mHy
>            3200V 1A Secondary -- 22 ohms DCR, 9H
>      A Westinghouse 1A, 10KV choke (50 lbs)
>            8H  & 30 ohms DCR
>   Doing "research" for a plate supply using microwave
>oven parts, I "recycled" a dozen microwaves, garnered
>from the "curb exchange", appliance "rated" from 600
>watts to 1 KW.
>   The transformers were all wound with #14 on the
>primary and #26 on the secondary.  The secondaries are
>all grounded at one end, though most can be easily
>lifted -- Negative lead filtering is a good option in
>this instance.
>   The secondary inductances measured between 9 & 22 H
>with the shunts in place.  The secondary resistances
>measured between 70 & 110 ohms.  They weigh from 8 to
>10 lbs each.
>   The capacitors run between .72uF and 1uF with the
>median around .9 uF.
>   Perhaps, two or three "matched" microwave
>transformer secondaries connected in parallel with 3
>or 4 of their caps connected in series, then across
>the transformers would be a good substitute for a real
>8Hy 1A choke. 
>     And a couple more data points for the resonant
>choke filtering thread:
>     The Collins 30S-1 used 8H & .15 uF in the plate
>supply and 3.5H and .5 uF in the screen supply.
>     I once used the 8H Westinghouse part noted above
>& .2uF at 5KV in a resonant configuration in my 4CX1000A
>power supply.  See:
>73 & Good afternoon,
>   Marv WC6W
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