[ARC5] JFET in ARC-5 TX oscillator socket

[mstangelo at comcast.net]

Where can you get cheap 1626's.

Mike N2MS

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

From: WA5CAB at cs.com

To: ARC5 at mailman.qth.net

Sent: Wed, 8 Jul 2009 04:05:39 +0000 (UTC)

Subject: Re: [ARC5] JFET in ARC-5 TX oscillator socket



1626's are cheaper than JFET's.  And for some strange reason work 

surprisingly well in Command Set transmitters.  You'd almost think that the sets had 

been designed to use them.



In a message dated 7/7/2009 10:32:03 PM Central Daylight Time, 

dennis.monticelli at gmail.com writes: 

> I forgot that it was a Hartley configuration.  You're right.  Output 

> would

> probably be low at the source node.

> 

> One way around that would be to choose a high Vp (pinchoff) JFET with a 

> high

> Idss rating and still protect it with a cascode device or else bias the

> drain from a separate voltage source.   I think the appropriate choice 

> would

> be a J111 (2N4856 or PN4856 is the same) or J108 (PN5432 is the same)  The

> latter is the most beefy.  In all cases the BV is at least 25V.  But these

> JFETs have more transconductance than the 1626 so the gate-source swing 

> will

> be less than the grid-cathode swing for a given current draw.  The optimum

> would be to change the tap on the coil but this is something most of us

> would prefer not to do.

> 

> Dennis AE6C

> 

> On Sat, Jul 4, 2009 at 10:31 AM, Ian Wilson 

> wrote:

> 

> >Not sure that beefing up the voltage dropped across a composite device

> >would

> >help, since it's a Hartley oscillator. The voltage swing is determined by

> >the

> >current through the device and the magnitude of the grid bias voltage

> >developed

> >(I think). Some other SS compound might have the right characteristics,

> >though?

> >

> >73, ian K3IMW

>