[ARC5] ARC-5 T-20 Frequency coverage and other questions
AKLDGUY .
neilb0627 at gmail.com
Fri Aug 1 02:25:19 EDT 2014
> I haven't actually done this exact conversion -- when I was a newbie, the
local area surplus store had literally a wall-full
> of T-19s -- but, the procedure would be somewhat thus:
>
> Set the dial to 4.5 mc.
>
> Take the VFO shield off (there is no H-bomb inside, despite the warning
label). Loosen the paint-locked set screws on
> the padder shaft, then crank the padder down toward mmaximum capacitance.
>
> Set the shield back into place.
>
> Apply power to the VFO (Osc Eb and Heater), see where the VFO is with the
dial reading 4.5 mc. If it's below 4 mc,
> open up the padder a little until it is at 4 mc.
>
> Set the dial to 4 mc. Power the VFO again, see if the VFO is actually at
3.5 mc. If it isn't, see if it can be brought to 3.5
> mc by adjusting the coil slug.
>
> Check the 4 mc point again, reset with the padder.
>
> Check the 3.5 mc point again, reset with the slug.
>
> Repeat the process until the dial tracks with 3.5 mc at the actual 4 mc
point, and 4 mc at the actual 4.5 mc point.
>
> Once you have the VFO tracked, replace all the shield screws and then
make final adjustments on the VFO with the
> slug and the little arm on the padder.
> Use the slug at the low end, capacitor at the high end... just like
tracking a receiver.
>
> Now for the PA. Set the VFO to 4 mc (4.5 on the dial). Unlock the
painted setscrews holding the rotor shaft of the PA
> padder. Apply plate and screen voltage to the PA. Dip the plate current
at 4 mc. Go down to 3.5 mc (4 mc on dial) and
> dip the plate current using the slug in the PA coil.
>
> BE CAREFUL! The slug has RF on it! Use an insulated tool. A metal
screwdriver is practically a necessity; make sure
> it fits the slot exactly and has a well insulated handle.
>
> Repeat the above procedure until the PA dip "tracks" between 3.5 and 4 mc.
> Voila! You have an 80 meter transmitter.
>
> I said I hadn't done THIS conversion... however, I have done something
similar to put a BC-457 on 160 meters (!!!). It
> required rewinding the MO and PA coils, of course. The tuning range came
out really sweet, 1.6-2 mc.
>
> The same procedure to fudge the BC-457 or T-20 down to 80 meters can be
used to move a 2.1-3 mc transmitter down
> to 160; I've done that too.
>
> 73
>
> Mike
> WA4DLF
Hi Mike
Sorry for the long delay in replying (due to time zone difference and
commitments during the day).
What you suggest probably is a great way to not only shift the tuning but
ensure it tracks over the 3.5 to 4.0 MHz range.
At the time I modified my T-20 I had heard that one shouldn't tamper with
the slugs, but now realise that's the only way to get the tracking correct
(a tedious job though).
I can't remember exactly what I did, but bear in mind that the year was
1967, accurate dial calibration all the way up the band wasn't important to
a 17 year old since it was perfectly acceptable to tune the VFO up the band
and zero beat it against the receiver BFO to get on the frequency of that
guy who was calling CQ.
Things were FUN in those days and the magic of it was that it worked, not
that one had perfect dial calibration.
73 de Neil ZL1ANM
On Fri, Aug 1, 2014 at 1:22 AM, Mike Everette <radiocompass at yahoo.com>
wrote:
> I haven't actually done this exact conversion -- when I was a newbie, the
> local area surplus store had literally a wall-full of T-19s -- but, the
> procedure would be somewhat thus:
>
> Set the dial to 4.5 mc.
>
> Take the VFO shield off (there is no H-bomb inside, despite the warning
> label). Loosen the paint-locked set screws on the padder shaft, then crank
> the padder down toward mmaximum capacitance.
>
> Set the shield back into place.
>
> Apply power to the VFO (Osc Eb and Heater), see where the VFO is with the
> dial reading 4.5 mc. If it's below 4 mc, open up the padder a little until
> it is at 4 mc.
>
> Set the dial to 4 mc. Power the VFO again, see if the VFO is actually at
> 3.5 mc. If it isn't, see if it can be brought to 3.5 mc by adjusting the
> coil slug.
>
> Check the 4 mc point again, reset with the padder.
>
> Check the 3.5 mc point again, reset with the slug.
>
> Repeat the process until the dial tracks with 3.5 mc at the actual 4 mc
> point, and 4 mc at the actual 4.5 mc point.
>
> Once you have the VFO tracked, replace all the shield screws and then make
> final adjustments on the VFO with the slug and the little arm on the padder.
> Use the slug at the low end, capacitor at the high end... just like
> tracking a receiver.
>
> Now for the PA. Set the VFO to 4 mc (4.5 on the dial). Unlock the
> painted setscrews holding the rotor shaft of the PA padder. Apply plate
> and screen voltage to the PA. Dip the plate current at 4 mc. Go down to
> 3.5 mc (4 mc on dial) and dip the plate current using the slug in the PA
> coil.
>
> BE CAREFUL! The slug has RF on it! Use an insulated tool. A metal
> screwdriver is practically a necessity; make sure it fits the slot exactly
> and has a well insulated handle.
>
> Repeat the above procedure until the PA dip "tracks" between 3.5 and 4 mc.
>
> Voila! You have an 80 meter transmitter.
>
> I said I hadn't done THIS conversion... however, I have done something
> similar to put a BC-457 on 160 meters (!!!). It required rewinding the MO
> and PA coils, of course. The tuning range came out really sweet, 1.6-2 mc.
>
> The same procedure to fudge the BC-457 or T-20 down to 80 meters can be
> used to move a 2.1-3 mc transmitter down to 160; I've done that too.
>
> 73
>
> Mike
> WA4DLF
> --------------------------------------------
> On Thu, 7/31/14, AKLDGUY . <neilb0627 at gmail.com> wrote:
>
> Subject: Re: [ARC5] ARC-5 T-20 Frequency coverage and other questions
> To: "J Mcvey" <ac2eu at yahoo.com>, "ARC-5 List" <arc5 at mailman.qth.net>
> Date: Thursday, July 31, 2014, 2:06 AM
>
> I can't now remember,
> it was so long ago.
> I have a vague idea I
> may have set 3.5 MHz as 4.5 on the dial.
>
> 73 de Neil ZL1ANM
>
>
> On Thu, Jul 31, 2014 at 3:18 PM, J Mcvey <ac2eu at yahoo.com>
> wrote:
>
> > I have one of
> those transmitters in pristine condition. I knew that
> > resetting the MO and final bandset caps
> was possible, but by how much? I
> > was
> thinking if I could bring it down exactly 1 MHZ then that
> would be an
> > easy interpolation on the
> original dial. Will it go down that far ?
> >
> >
> > On Wednesday, July 30, 2014
> 10:22 PM, AKLDGUY . <neilb0627 at gmail.com>
> > wrote:
> >
> >
> > Many decades ago I
> shifted a T-20 (4-5.3 Mc/s) to the 80m band simply by
> > unlocking and resetting the VFO and PA
> bandset capacitors.
> >
> > I'm almost certain that allowed
> coverage of the entire CW portion, because
> > IIRC that was my first ARC-5 transmitter
> and I had it ready to go on the
> > day my
> ticket arrived in the mail and worked Russ ZL4JW on CW the
> same
> > night (27 October 1967). I was at
> North Shore, Auckland and he was at
> >
> Omarama near Dunedin. Still have the original log book.
> >
> > Can only suggest you
> try resetting those bandset capacitors before
> > attempting any "recommended"
> mods.
> >
> > 73 de Neil
> ZL1ANM
> >
> >
> > On Thu, Jul 31, 2014 at 9:10 AM, Andrew
> Kopke <andrewkopke at rocketmail.com>
> > wrote:
> >
> > > Hello all, I'm new to the group
> and a new owner of a ARC-5 T-20
> > >
> > > After doing some reading on line ,It
> appears as though this model could
> > >
> cover the 80 meter band mentioned in one of the conversion
> manuals ( I
> > > think it was
> "Command Sets" published by CQ ) Anyway, That mod
> mentions
> > > adding a capacitor
> somewhere . There is another modification that
> > involves
> > > C-60
> and, making the plates of that capacitor fully meshed. I
> took the
> > > cover off and sure enough
> the paint seals were broken and the capacitor
> > was
> > > closed.
> > >
> > > I
> haven't even begun building the power supply as of yet .
> I do have a
> > > 24v dc 2.5 amp
> supply.
> > > I have alot of questions
> to follow ,but my first question is :does anyone
> > > know if this transmitter will cover
> the bottom CW portion of the 80 meter
> >
> > band with the plates of C-60 closed? I don't see
> any other modifications
> > > done. I
> washed the set in the sink with dawn and rinsed with
> distilled
> > > water unfortuately, I
> washed off the white ink behind the plastic window
> > > of the roller inductor scale ,but can
> still see the number scale engraved
> >
> > in the plastic. I suppose I could just get a white
> paint marker and re-
> > do
> > > it . Any thoughts?
> > >
> > > Thanks for
> any insight,
> > >
> >
> > Andrew Kopke
> > >
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