[Boatanchors] DX 100

[John Lawson]

>
> ----- Original Message ----- From: "Joe Dube" <jdube1 at bellsouth.net>
> To: <Boatanchors at mailman.qth.net>
> Sent: Wednesday, November 28, 2007 5:43 PM
> Subject: [Boatanchors] DX 100
>
>
> I need a bit more help with the DX 100. Can anyone out there give me an idea 
> of what might be the problem with my DX100 slowly falling Grid current. This 
> happens after I peak the grid current to about 5 mils  and then key the 
> transmitter. It will hold for a few moments and then begin to fall to zero. 
> At this point the plate current goes all the up to the end stop and I have to 
> shut the plate switch off quickly.  This happens with a crystal as well as



    Disclaimer - I don't have the DX-100 schematics to hand, and I last 
owned one in the mid 70s...


   If somehow the grid bias is derived from, or passed thru, a resistor 
that is bypassed or decoupled with a fairly large capacitor - and this 
resistor is open, or failed at a very high resistance - then the bias 
circuit would 'charge' at idle, then discharge under (grid) load - and 
might exhibit exactly the symptoms you report.

   [You DO have the schematic in front of you, at least?]

   Many times, when there's a failure that "takes it's time" to manifest 
like this, a timing circuit has been 'created' by the failure, and a bit 
of VOM work might get you right to the part(s) that are giving you so much 
grief.


   Here's hoping you have the satisfaction of nailing another "tough dog" 
of a bench problem!


  Cheers

John KB6SCO
Carson City