[ARC5] T-19 Update

Fri Dec 21 07:49:47 EST 2012


> Date: Friday, December 21, 2012, 7:48 AM
> I read Chris's message wrong last
> night... too many hours of no sleep for the past few
> days.  Dave Stinson, I do know better...!

There is ONE relay in the modulator which keys
> the transmitter (this is exclusive of the dyno-starter), and
> all the B plus goes through it -- oscillator, PA screen, PA
> plate.
> 
> Usually when I "converted" Command transmitters, I used the
> under-chassis relay to key the oscillator cathode and PA
> screens.  Several other arrangements were tried 
> including the oscillator plate and PA cathode (as the relay
> is originally wired), but that method in particular caused a
> lot of sparking at the relay contacts and consequently
> created key clicks.  I tried R-C networks on the
> contacts to suppress this but it didn't help much.  In
> my oscillator-cathode-keying circuit, I seem to recall using
> a 2.5 millihenry choke in series with the cathode, probably
> bypassed to ground with something like an 0.001 uF
> cap.  The signal still had a slight chirp, but who
> cares... it had CHARACTER.
> 
> It has been quite some time since I even looked inside one
> of those converted transmitters, but maybe it should be dug
> out... I might just try to use them on Field Day next
> June.  
> 
> It's so much fun to confound the Codeless & Clueless
> with what a huge score can be compiled on CW... and with
> vintage gear, too.  "Whut?  TOOBS?  Ah ain'
> neva' seen no raidyos lak theyat...."  " 'N y'mean
> y'kin copy that skwee-dubya wit'out no code reader? 'N send
> it wit'out no key board?"  "DAYY-ummmm.!"
> 
> 73
> 
> Mike
> W4DSE
> 
> --- On Thu, 12/20/12, Mike Everette <radiocompass at yahoo.com>
> wrote:
> 
> > From: Mike Everette <radiocompass at yahoo.com>
> > Subject: Re: [ARC5] T-19 Update
> > To: "David Stinson" <arc5 at ix.netcom.com>,
> "ARC-5 List" <arc5 at mailman.qth.net>,
> "Christopher Bowne" <aj1g at sbcglobal.net>
> > Date: Thursday, December 20, 2012, 7:02 PM
> > Chris, you are quite correct in your
> > analysis.
> > 
> > I've been following this thread but have not jumped in
> until
> > now... it really surprises me that there could be so
> much
> > trouble with an ARC-5 transmitter.  Could it be
> > something as simple as the connection between the
> little
> > coil spring contact which the "antenna" relay moves to
> > select the transmitter, not making to the antenna
> > post?  Hmm.
> > 
> > If the little spring is missing, is there any sort of
> > connection between the antenna post and the "arm"
> which
> > comes up from the loading coil, where the spring would
> > normally be?
> > 
> > Or, try this.  You might be surprised to find out
> that
> > the antenna loading coil has become so oxidized that
> there
> > is no connection between the wire and the roller
> > contact!  Yes, it COULD be, indeed.  Seen it
> > before.
> > 
> > Use some contact cleaner and a paper towel; scrub the
> > winding of the coil, then clean the roller and the
> brass
> > shaft that it runs on.  You do not have to
> disassemble
> > anything or remove it from the transmitter.
> > 
> > DO NOT start turning the two screws with blue heads,
> which
> > are the slugs in the VFO coil and the PA tank coil. 
> > You will really regret doing that.
> > 
> > 73
> > 
> > Mike
> > W4DSE
> > 
> > 
> > --- On Thu, 12/20/12, Christopher Bowne <aj1g at sbcglobal.net>
> > wrote:
> > 
> > > From: Christopher Bowne <aj1g at sbcglobal.net>
> > > Subject: Re: [ARC5] T-19 Update
> > > To: "David Stinson" <arc5 at ix.netcom.com>,
> > "ARC-5 List" <arc5 at mailman.qth.net>
> > > Date: Thursday, December 20, 2012, 6:53 PM
> > > IIRC, the modulator BC456 and MD7
> > > modulator power units only actually key the MO 
> > > plate and final screen voltages to transmit on CW
> and
> > MC
> > > ,with the 1625 plates 
> > > having HV on them  whenever the dyno is running,
> > which
> > > is continuously in CW and 
> > > MCW.  Of course in voice mode, the dyno itself
> is
> > keyed
> > > to start on transmit.  
> > > What some think is a "keying" relay in the final
> > cathode
> > > circuit is actually the 
> > > TX "select" relay which, in a multi transmitter
> setup,
> > > returns the cathodes to 
> > > ground of the set that is selected by the
> transmitter
> > select
> > > switch on the TX 
> > > control box, the same circuit also  locks  on
> the
> > > transmitter's antenna connect 
> > > relay to connect the tank circuit to the antenna
> > post. 
> > > Neither of these relays 
> > > on the transmitter chassis otherwise follows
> keying in
> > the
> > > original design.  The 
> > > external antenna relay that shifts the antenna
> from
> > the
> > > transmitter to the 
> > > receivers does follow keying of course.
> > > 
> > > This is based on my memory from when I set up my
> > "hybrid"
> > > ARC-5/274N system of 
> > > T19/T22 transmitters, BC-456 modulator, and ATA
> > antenna
> > > relay (one of those with 
> > > the build date clipped off the nameplate), and
> BC-450
> > > transmitter control box.
> > > 
> > > Chris, AJ1G
> > > Stonington, CT
> > > 
> > > 
> > > ________________________________
> > > Frh, inom: David Stinson <arc5 at ix.netcom.com>
> > > To: ARC-5 List <arc5 at mailman.qth.net>
> > > Sent: Thu, December 20, 2012 8:17:59 AM
> > > Subject: Re: [ARC5] T-19 Update
> > > 
> > > Fellow ARC-ites:
> > > 
> > > Can a couple of you please take a few minutes to
> look
> > at the
> > > ARC-5 and 274N 
> > > modulator power distribution
> > > diagram and see if I got these right?  I've
> checked
> > > repeatedly, but I'm just a 
> > > human... I can make mistakes.
> > > If everything is "right," his rig should be
> working.
> > > If I ever actually built these dividers, I don't
> > remember
> > > it.
> > > I run my rigs with the original modulator and
> racks.
> > > 
> > > http://home.netcom.com/~arc5/ARC5/ARC5PWR.jpg
> > > 
> > > http://home.netcom.com/~arc5/ARC5/274NPWR.jpg
> > > 
> > > 
> > > 
> > >
> >
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