Re: {Collins} 32s1 balanced modulator update



My apologies for misquoting John. It must have been someone else who reported good results with 1N4148's -- or maybe I just remembered the whole thread wrong!!

73
Bob


On 12/2/2012 12:28 PM, johnbess@xxxxxxxxxxxx wrote:
Hello all,
I have never recommended the 1N4148 (If so I must have been in another stast of mind). I always used 1N34 matched sets for all of them. (I had about 500 to choose from at the time.) The shottky would be my pick at this time.
73's, John, Bess, W A 5 V V T


-----Original Message-----
From: Bill Carns <wcarns@xxxxxxxxxxxxx>
To: ve3tou <ve3tou@xxxxxxxxxxxxxxxxxxx>
Cc: COLLINS <COLLINS@xxxxxxxxxxxxx>
Sent: Fri, Nov 30, 2012 2:31 pm
Subject: Re: {Collins} 32s1 balanced modulator update

Guys,


In deference to John, the 1N4148 may "work well" as a "matched set" of
balanced modulator diodes replacing the venerable 1N34, but....

The 1N34 is a germanium diode and there is a reason that Collins stayed with
a germanium for so long. Germanium diodes have a forward voltage of
approximately 0.3 volts. A silicon diode has a forward voltage of about 0.7
volts or 0.4 volts higher that a germanium. If you use a more modern (and
yes more planar and more matched than random 1N34s), you will get a working
balanced modulator but it will not work as well as the original.

The solution is to use a modern Shottky diode (typical forward at or a
little below germanium) or a modern manufactured germanium like the 1N270.

This is readily available and, taken out of the same batch (off the same
tape, or with the same date code), they will be perfectly matched and
provide better performance than the original 1N34 diodes.

If you want to try a Shottky, try a 1N5711. Others may have other
suggestions but any small signal hot carrier diode will work.

I would not use a silicon diode that was not a Shottky hot carrier diode.
You are going backwards if you do this.


Bill Carns, N7OTQ
K0CXX, Trustee MRCCC
President Collins Collectors Association
Editor, Signal Magazine
Founding Member # AC94-0009
512 618 2762 (Cell + VM)
512 847 7010 (Home + Fax)




-----Original Message-----
From: Collins [mailto:collins-bounces@xxxxxxxxxxxxx] On Behalf Of Robert
Thomas
Sent: Friday, November 30, 2012 1:29 PM
To: Doug Crompton
Cc:collins@xxxxxxxxxxxxx
Subject: Re: {Collins} 32s1 balanced modulator update

I believe John Bess and possibly others have made a practice of using
1N4148's routinely in balanced modulators. As has been pointed out before,

modern (at least relatively modern!!) diodes are made using the planar
process, which generally gives a good degree of matching  within a
production batch.

All of this will be in the reflector archives, which gives us one more
reason to look forward to their return!

73
Bob


On 11/30/2012 1:08 PM, Doug Crompton wrote:
> I have a 32s1 that has not had the service bulletin modification for the
balanced modulator which is basically adding two 1n34a's and a resistor. My
question is the replacement diodes. I have to check but I may not have two

good 1n34a's in the junkbox. I presume these need to be germanium diodes? Do
the 4 have to be matched? I am curious if anyone else has made this mod and
used different diodes. I do have a slew of 1n4148's but these are silicon
signal diodes.
>
>
> 73 Doug
>
> WA3DSP
>www.crompton.com/hamradio
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_______________________________________________
SHARE THE FUN: JOIN THE COLLINS COLLECTORS ASSOCIATION TODAY !
http://www.collinsradio.org/?page_id=37

  NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific
   SUNDAYS: 14.263 MHz-2000 UTC  +  AM Net: 29.050 MHz-1200 Central
   1st Wednesday AM Net 3.880 MHz-2000 local (ET, CT, MT, PT)

The Collins Reflector reserves the right to refuse access to anyone.

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