[HBR] pots required HBR13.

[Tony]

Hi Bill,

here's my two cents;

The IF pot is connected between ground and 250V B+ in series with a 75K resistor( the HBR-16 IF pot is 15K).

If I remember my Ohm's law P= E*/R = 62,500V/90,000 OhM = .69W.

The current thru the pot would be 250/90,000 = 2.8Ma.

Using the same approach the RF gain pot would be 62,500/70,000 = .89W

The Mixer pot would be 62500/83,000 = .75W

Where am I going wrong?

Must be some other reason for the large wattage pots.

Tony WV3Z




--- On Sun, 2/1/09, Bill Fizette <w2dgb at ptd.net> wrote:

> From: Bill Fizette <w2dgb at ptd.net>
> Subject: Re: [HBR] pots required HBR13.
> To: "Walt Hutchens" <waltah at earthlink.net>, "HBR Receiver List" <hbr at mailman.qth.net>
> Date: Sunday, February 1, 2009, 11:25 AM
> Having just fought the battle of trying to find the WW pots
> that ole' TC 
> specified for the HBR 13 I am building, I am now getting
> curious as to why 
> he did specify that these particular 5 watt components were
> needed.  The 
> current through the IF pot, for example is somewhere around
> 22 ma, I am 
> told.
> Would not the readily available AB sealed pots work here?  
> If not, why? 
> What am I missing here?
> 
> Bill  w2dgb
> 
> 
> ----- Original Message ----- 
> From: "Walt Hutchens"
> <waltah at earthlink.net>
> To: "HBR Receiver List"
> <hbr at mailman.qth.net>
> Sent: Sunday, February 01, 2009 6:06 AM
> Subject: Re: [HBR] pots required HBR13.
> 
> 
> >> Can someone please direct me to a supplier of the
> pots as used in the 
> >> HBR13.
> >> The values are 2K, 10K, and a 5K. All are 5W.
> >
> > Mouser is one supplier, Antique Electronic Supply is
> another.  Five
> > minutes with Google will find others.
> >
> > One issue that's new in recent years, particularly
> with places as big
> > as Mouser, is the number of choices. In particular
> watch out for
> > metric parts with 6 mm shafts and 8 mm bushings. Read
> the specs
> > closely before ordering.
> >
> > That wattage requirement will narrow your choices
> some: Those will
> > have to be wirewound.
> >
> > Come to think of it, wirewound pots don't usually
> go permanently bad
> > unless they're overloaded.  Have you tried just
> working them back and
> > forth a couple dozen times?
> >
> > Walt
> > KJ4KV
> >
> >
> >
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