# [Amps] resonant choke filters.

Jim Thomson Jim.thom at telus.net
Sun Feb 21 04:07:51 PST 2010

```Date: Sat, 20 Feb 2010 11:29:34 -0600
From: "Roy" <royanjoy at ncn.net>
Subject: Re: [Amps] 120 Hz hum from Henry...

"Be careful if you fix this. It's not tuned to *exactly* 120 Hz because that
would cause a very high voltage to appear across the choke. Use the specified values if
you replace anything."

I strongly believe the above is a perpetuated old hams' tale, totally
untrue. The parallel-tuned circuit is a frequency-rejection filter,
exhibiting a very high Z to the 120 Hz ripple, thus preventing high
circulating current and its resultant voltage build up. Read the article,
noting the careful tuning to exactly the 120 Hz resonant frequency:
http://www.qsl.net/i0jx/supply.html

73,   Roy    K6XK

&&& IF you resonate the filter to exactly 120 hz... the resonating  cap
WILL  blow up in your face. Try it and you will see for yourself. Been
there, done that.    Ask Tom Rauch  abt his resonant choke experiences,
he just abt killed himself.

&&&  also note in the I0JX article.  He uses SIMULATIONS. That`s
fine, but apparently the simulations  don`t show the exploding cap.

&&  also note he advocates using swinging chokes. Swinging chokes
are a dead loss, if used in resonant filters. Their inductance is all over the map,
exactly what you don`t want.  Dahl`s chokes, made for resonating, are very stiff, and
only drop down in value a small amount, when a huge load is applied.

&&  Look at his plane jane  C input filter.. just ONE 15 uf cap.. 6450 vdc  No load,
and  6175vdc, sucking 1000ma.    6147 divided by 6450 = .957   That`s  a
4.3% drop. That`s  superb regulation.   If he had increased the C  to 50-150uf,  you
will then get a real eye opener. Loaded V is higher.. and on SSB, it won`t droop at all.

In his henry 4 K ultra  example... his No load = 4525vdc.  His loaded V = 3950vdc.
3950 divided by 4525 = .873    This is a 13%  DROP !    So much for the nonsense abt
the infamous Henry radio resonant chokes.They are heavy alright, but they are not heavy duty.

The 8 K ultra used a resonant choke.  It also sucks 300 w of bleeder, just to make the choke,
look like a choke. ( 5 x 20 k, 100 watt  WW`s in series)  No load is 5400 vdc.  To get that,
they use a 6000 vac xfmr.   If that had been a simple C filer, only a 3800 vac  xfmr is needed...
(and NO choke, nor 300 W  CCS  bleeder)   Loaded V on the 8k = 4800 vdc ,
4800 divided by 5400  = .888    again, no fantastic regulation here. (11.1% drop)

IMO, ur better off to dump the resonant choke,and spend the money on the xfmr, and caps,
not a bunch of excess weight.   Besides, any resonant choke set up will not kill the harmonics
very well.   The plane jane... BIG C input filter, will kill the 120 hz ripple,,, and ALL the
harmonix of 120 hz.

later... Jim  VE7RF
```