Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/5/84; site yojna1.UUCP
Path: utzoo!linus!philabs!cmcl2!harvard!seismo!umcp-cs!aplcen!cp1!yojna1!wb6rqn
From: wb6rqn@yojna1.UUCP (Brian Lloyd)
Newsgroups: net.ham-radio
Subject: Re: Re: Replacement FET for Heath scopes (and other scope comments)
Message-ID: <128@yojna1.UUCP>
Date: Wed, 13-Nov-85 12:51:14 EST
Article-I.D.: yojna1.128
Posted: Wed Nov 13 12:51:14 1985
Date-Received: Sun, 17-Nov-85 05:35:13 EST
References: <21464@mgweed.UUCP> <154@tapa.UUCP>
Organization: Yojna1 Amateur Radio Packet Unix System; Germantown, Md.
Lines: 26

> [...]  The front end is a FET differential pair which has a bad
> DC drift with temperature (the 4510 is DC coupled).  Once after leaving it
> on in the upright position for 3 days the DC offset (kinda dumb anyway) the
> DC offset went too far for the trimmer pot rendering it useless.
> 
> Has anybody got any ideas about a cheap fast front end, DC to about 25mhz.
> which I can use to replace the fet front end?
> 
> Larry WA9QOO
> ihnp4!tapa!larry

The temperature problems with DC balance might be cured by making sure that
the two devices in the diff pair are thermally connected.  Several of the 
semiconductor mfgrs make matched diff pairs in a single package.  These are
very fast and very closely matched.  Try Siliconix, they have some.  I looked
very quickly and they have a dual that is designed for wideband differential
amp applications.  The device number is 2N5564, -65, and -66.  I am sure that
there are other vendors, and you didn't specify the parameters needed (gfs, 
quiescent current, etc.).

73 de Brian, WB6RQN

Brian Lloyd
...![bellcore!cp1]!yojna1!wb6rqn

P.S.  Also look at 2N5911