[AMRadio] DX-100B, output falls off gradually

[Gary Schafer]

Hi rick,

Also check to see if you have the mode switch in AM or CW. 
Only in the AM position does the plate switch ground/open the cathode
circuits. In the CW position the cathodes are connected directly to the CW
key jack which has shorting contacts when the key is unplugged.

So if you have the mode switch in CW and the key unplugged, then the
cathodes of the VFO and buffer are always grounded.

73
Gary  K4FMX

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of Rick Poole
> Sent: Saturday, November 19, 2011 10:13 PM
> To: amradio at mailman.qth.net
> Subject: Re: [AMRadio] DX-100B, output falls off gradually
> 
> At 09:01 PM 11/19/2011, Gary Schafer wrote:
> 
>  >>>>>
> >Check to see if there is a jumper wire on the accessory (8 pin socket)
> on
> >the back plugged into pin 1 to ground.
> <<<<<
> 
> Good evening, Gary.
> 
> There isn't a jumper, but there is continuity between pin 1 and
> ground regardless of the position of the Plate switch.  I did check
> the schematic and pin 1 is connected, through a choke, to the hot end
> of the side of the Plate switch that connects to the Phone/CW switch
> and thence to the cathodes of the VFO and buffer tubes.  So, that
> side of the Plate switch (and, the cathodes of the VFO and buffer
> tubes) are always grounded whether the Plate switch is on or not.
> 
> That explains a lot; in addition to explaining this issue, it also
> explains my other issue, that I get a "spotting" signal in the
> receiver even when I don't have spotting turned on.
> 
> When I bought this transmitter, it came with an SB-10, and I'm pretty
> sure the previous owner meant to only use it in SSB and never in
> AM.  So it looks like there is some undocumented mod made on the
> assumption that it would never be run in AM (although the previous
> owner was very good about documenting things... the manual is
> liberally marked up in many different places with lots of notes).
> 
> I'll have to get ahold of the previous owner... he has been very
> helpful to me in the last couple of weeks although he does take a
> long time (many days) to answer email.  Meanwhile I'll open 'er up
> and trace down what he did.
> 
> Thanks for the pointer, looks like you were spot on...
> 
> Rick WA1RKT
> 
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