Re: {Collins} kwm-2 balanced modulator replacement



I believe the 1N5711 Schottky diode was mentioned in a similar thread some time back. These things aren't rare. Go to www.digikey.com and search on 1N5711. They're around 40 cents each in quantities of 10.

73
Bob


On 2014-07-29 8:29 PM, Bill Carns wrote:
Hi, Well, the idea of using a Schottky diode in the balance modulator - and
yes, go for a quad for better performance - is a great way to replace those
earlier low Vf Germanium diodes. In fact, Schottky diodes have a very low
forward and with today's modern semiconductor processing, from a practical
standpoint, matching is very unnecessary as long as you get your diodes from
the same source & out of the same date code. Paying $60 for a quad is not
necessary at all.

The 1N4007, although ubiquitous, and very good at many things, is a very
poor choice for the 1N34 replacement because the 1N4007 is a Silicon Diode
and has a Vf almost twice as high as the older Germanium.  Do not go there.
Your balanced modulator performance will suffer.

If you have difficulty find some Schottkys, give me an off line email and I
can probably help - if I can find them.  :-)

Regards,

Bill Carns, N7OTQ
Trustee K0CXX
President, Collins Collectors Association
Editor, Signal Magazine
Wimberley, TX
512 618 2762  (Cell)
512 847 7010  (Home)



-----Original Message-----
From: Collins [mailto:collins-bounces+wcarns=austin.rr.com@xxxxxxxxxxxxx] On
Behalf Of Roy Morgan
Sent: Tuesday, July 29, 2014 6:08 PM
To: Steve Berman
Cc: David F. Reeder via Collins; Brad Thompson
Subject: Re: {Collins} kwm-2 balanced modulator replacement

Collins Balanced Modulator folks,

I don't think we need to spend $60 for a set of diodes.

HP made many types of schottkey diodes, some of exotic sort and some of a
more common type.  These have been suggested as replacements for the
balanced modulator in our S-line radios.  I seem to remember the 1N4007
suggested as a replacement.  This diode is not as simple as the
few-cents-each price would suggest.

My long time friend Brad Thompson has in the past had some Schottkey diodes,
and draws upon his experience as a components engineer to have opinions and
suggestions about them.  I've copied him on this and will forward any
replies he sends me about the topic (I think he's not on the Collins list).

Roy


On Jul 29, 2014, at 6:11 PM, Steve Berman <n6hk@xxxxxxxxxxx> wrote:

Try Four Star Electronics in San Clemente,  CA.   They have the CA 6987
diode quad packs in stock.   They're about $60 each.
Steve, N6HK

-----Original Message-----

From: Tom Worthington
Sent: 29 Jul 2014 21:25:36 GMT
To: collins@xxxxxxxxxxxxx
Subject: {Collins} kwm-2 balanced modulator replacement

I am working on an early KWM-2, S/N 200.  It has the balance modulator
version with 1n34A germanium diodes and some are defective.

I can replace with new 1n34a's but I would prefer to use a matched
diode ring and upgrade to the mod 5 version but I haven't been able to
find a source.

Are there any recommended replacements?

73, Tom, NH6Y
...
Roy Morgan
RoyMorgan@xxxxxxxxxxxx
K1LKY Since 1958

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