[R-390] 6DC6 Replacement

[Steve Goode]

Alex,

In my quick search for high voltage FETs I have only found one reference.
InterFET makes a 2N6449.  I have not found a distributor for them.  I have
an HW-100 that I want to do the relay driver mod on as you describe.  The
relay seems to take out that tube every couple of years.

73,

Steve, K9NG


----- Original Message -----
From: "AI2Q Alex" <ai2q@adelphia.net>
To: "'Steve Goode'" <goode@tribeam.com>; <r-390@mailman.qth.net>; "'Roger L
Ruszkowski'" <rlruszkowski@west.raytheon.com>
Sent: Wednesday, January 16, 2002 10:38 AM
Subject: RE: [R-390] 6DC6 Replacement


>
> Hi Steve:
>
> I confess! I've poked JFETs into both 26C6 mixers on my R-392, and those
> 24-V stages work really well. I used a Dremel tool cutter to scribe the
> glass of 7-pin miniature tubes, cracking them open and removing the
innards.
> I then soldered the JFETs with drain source and gate connected to the old
> plate, cathode, and grid leads, respectively. After inserting a label with
> my callsign on it, I then glued the glass envelopes closed. I popped 'em
> into the R-392, where these solid-state jobbies perform flawlessly. I can
> elaborate about the glass cutting procedure if you're interested.
>
> As per the 1977 QST article, last night I fired up an 1800-volt bipolar
> junction transistor in the relay circuit of an old Drake TR4. The device
is
> a TV horizontal output transistor.
>
> I pulled the relay driver tube and put my little solid-state jobbie
(fabbed
> on a scrap of circuit board) in there with some clip leads, with my VTVM
> hanging in to see what's happening with the switching levels. I also put a
> reverse-biased diode across the driven relay in order to quash any
possible
> counter-EMF that might do in the transistor. The xstr that drives the
relay
> is in turn driven by a cheap N-channel JFET such as an MPF-102 or MPF-105,
> which derives its Vdd from a diode and a 300 uF cap hanging off the
filament
> line as a simple halfwave rectifier/filter. The FET gate is extremely
> high-Z, and sees the control voltage at a VOX/anti-VOX summing point.
Works
> like a champ and offloads the filament line.
>
> Now on to RF "replacements." Finding suitable high-voltage FETs for the
> cascode circuits may be a problem. The Idss of the output FETs in these
> pairs has to complement the input FET. As for dual-gate MOSFETs, I know
that
> Dan's Small Parts has some.
>
> Your thoughts?
>
> Vy 73, AI2Q, Alex in Kennebunk, Maine   .-.-.
>
>