[ARC5] ARC-5 T-20 Frequency coverage and other questions
Mike Everette via ARC5
arc5 at mailman.qth.net
Thu Jul 31 09:22:45 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
--------------------------------------------
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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