[R-390] 3TF7 Substitutes

[Cecil Acuff]

There are any number of complex ways to solve the 3TF7 issue but we should
not be short sighted and forget about any noise that might be generated by
the solution.  Linear regulator circuits work great but are quite noisy.

The new fangled sand box radios suffer from many problems associated with
noise generated by devices internal to the radio...fortunately the 390
series doesn't have that problem....that's one of the things that makes it
such a stand out performer.

Cecil...
----- Original Message ----- 
From: "David Wise" <David_Wise at Phoenix.com>
To: <r-390 at mailman.qth.net>
Sent: Friday, September 24, 2004 3:29 PM
Subject: RE: [R-390] 3TF7 Substitutes


> -----Original Message-----
> From: mikea [mailto:mikea at mikea.ath.cx]
> Sent: Friday, September 24, 2004 10:29 AM
> To: r-390 at mailman.qth.net
> Subject: Re: [R-390] 3TF7 Substitutes
> cause of this drift.
>
> Thanks _very_ much for your research results. I have had the benefit
> of your expertise for some years now, and think it is appropriate to
> give you your due in public.
>
> I feel some construction coming on.

If you're in the mood for construction and would prefer to make
*no modifications whatsoever* to your radio, you might consider
the 3DW7A, which I designed a while back.  Thanks again to Roy Morgan
for massaging the picture into a portable format.  I tried to post
it here, but the listserv rejected the .jpg attachment.  Contact
me off-list and I'll email it to you.  The single-source items
(the MOSFETs and the RMS converter IC) are available at DigiKey.
Everything else is generic.

It's a cool-running two-pin module, although you'll
need a magnifying glass and tweezers to cram it into
the "tubester" form factor like I did.  Maybe I ought to
post a photo of the completed unit to prove it can be done.

By the way, I'm still working on the 3DW7D, which does the
same job digitally at about 1/2 the parts count.  Somebody
asked for a LED to simulate the olde-tyme glow, and I got
carried away.  Soon (but that means < 5 years :)

73,
Dave Wise (SWL)
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