Hi, I'm building a PSU and inteface for an old ARC5 transmitter its the
one that covers 40mtrs, I only want to use it on CW I've fired it up
and tested it, and up to 10 watts its not to bad, I know it will be a
little chirpy owing to it being just an MO into a PA, but over 10 watts
the chirp becomes a real squawk hi! has anyone ever heard an ARC5 at
full gallop ie 30watts? are they really squawky at full power or is it
back to the drawing board
from Ron...

ron_ayling wrote:

Hi, I'm building a PSU and inteface for an old ARC5 transmitter its the
one that covers 40mtrs, I only want to use it on CW I've fired it up
and tested it, and up to 10 watts its not to bad, I know it will be a
little chirpy owing to it being just an MO into a PA, but over 10 watts
the chirp becomes a real squawk hi! has anyone ever heard an ARC5 at
full gallop ie 30watts? are they really squawky at full power or is it
back to the drawing board
from Ron...

I got OO reports from about 17 states when I was a Novice using my ARC5
on 40 meters. That was in 1970 - back when people weren't so picky.

-Bill ex-WN4SXX

On 1 Feb 2005 11:30:01 -0800, "ron_ayling"
wrote:

Hi, I'm building a PSU and inteface for an old ARC5 transmitter its the
one that covers 40mtrs, I only want to use it on CW I've fired it up
and tested it, and up to 10 watts its not to bad, I know it will be a
little chirpy owing to it being just an MO into a PA, but over 10 watts
the chirp becomes a real squawk hi! has anyone ever heard an ARC5 at
full gallop ie 30watts? are they really squawky at full power

Yes.


or is it
back to the drawing board

Best to run the oscillator continously (while transmitting) and just
key the finals. And then figure on some key click filtering.


N7WS

Bill M ) writes:
ron_ayling wrote:

Hi, I'm building a PSU and inteface for an old ARC5 transmitter its the
one that covers 40mtrs, I only want to use it on CW I've fired it up
and tested it, and up to 10 watts its not to bad, I know it will be a
little chirpy owing to it being just an MO into a PA, but over 10 watts
the chirp becomes a real squawk hi! has anyone ever heard an ARC5 at
full gallop ie 30watts? are they really squawky at full power or is it
back to the drawing board
from Ron...

I got OO reports from about 17 states when I was a Novice using my ARC5
on 40 meters. That was in 1970 - back when people weren't so picky.

But wouldn't that have been because the US Novice license didn't allow
the use of VFOs until 1972?

Micahel VE2BVW

Michael Black wrote:


But wouldn't that have been because the US Novice license didn't allow
the use of VFOs until 1972?

Micahel VE2BVW


Ssshhhh!
Actually its kind of funny. As you know the dial readout on the ARC5 is
fairly precise and easy to read. I was very paranoid about using the
VFO and only used about 5 particular favorite frequencies for fear that
"they" would hear me all over the band.
Seems so silly nowadays with CBers raising havoc scot-free from 24-29 Mhz!

-Bill

ron_ayling wrote:
Hi, I'm building a PSU and inteface for an old ARC5 transmitter its the
one that covers 40mtrs,...
I know it will be a
little chirpy owing to it being just an MO into a PA, but over 10 watts
the chirp becomes a real squawk hi!...

I've spent many years with these rigs.
If you have removed the relays and done the usual "hamming"
modifications, getting rid of all the chirp may not be possible.
Chirp is addressed about half way through all this.
The "standard" ham modification is a very bad one.

Here is a "replay" of a couple of posts I made
to other lists that some have found useful.
Chirp is addressed about half way through all this.
I hope they may provide some help.
----------

The only "modifications" needed to a Command transmitter
are simple and 100% restorable.

1. Replace the three capacitors in the bathtub on the back.
Even if you think they're good, they're bad. Trust me on this.
Leakage in this bathtub cap causes big headaches,
and if it isn't leaking now, it will be.
Here's an easy way:
Unsolder the leads of the bathtub cap, leaving the wires intact.
Make sure multiple wires stay connected to each other, just not the cap.
Coat them with insulation. "Liquid Tape" by GC is good and available
at most electronics parts places, or just use tubing.
Leave the wires where they are as their distributed capacitance
is part of the design.
Get some of those little mylar .047s from the parts house.
They're about the size of a pencil eraser. Trace the wires from
the bathtub to where they connect, then solder the cap between
there and the nearest ground.

2. Unsolder one lead from the antenna relay. Roll the spring
contact from the loading coil around so it's always in contact.
Either put some Cramolyn on this contact or polish it as
detailed below.

3. Check the selector relay and make sure that the osc. B+
contact (the "short" one, nearest the coil)
makes before the 1625 cathode contact. Carefully bend
them to make sure. You key the rig with this relay
through it's contact on the back plug- it's called the "selector."
Put a "spike killer" diode across the relay coil winding
(anode to positive voltage lead) to keep the inductive
kick off the filaments and keying leads.

That's it. All the hole drilling and output hacking and
"de-TVIing" of the 50s and 60s was completely unwarranted.

If you want to make it easy to tune and remove
a source of possible "chirp," the next steps are
some work, but well worth the effort-

All the roller coil assembly metal parts (less screws)
are plated in silver. This gets oxidized (that black stuff).
When you're loading the rig, you'll notice "intermittent" power
out as you roll over the gunk. If your loading point is
cruddy with this black stuff, it will heat when you key
and change the loading enough to introduce some chirp
(yes, believe it or not).

Go to Wally World and get some cream silver polish.
Don't waste your money on the "dip" stuff.
Put a towel or other "parts catcher" on your bench.
Completely disassemble the roller coil unit.
Pay close attention so you can get it back together
in the right order.
The leaf-spring contact on the coil axle (ceramic support end)
needs to go back right-side-up, so you might want to mark it
or just notice how it goes back in.
Use a linen or other lint-free cloth to polish the coil,
roller bar, roller, axle leaf spring contact etc.
Use a "Q" tip to polish the inside of the roller wheel as well.
Once all the crud is polished away, rinse off all the polish
with clean water and allow the parts to completely dry-
especially the coil. Don't want water under the turns.

As you reassemble, lubricate the thumb-wheel end and thumb-wheel
axles with petroleum jelly or graphite. Do not lube the
ceramic-to-coil joint, but do lubricate the roller coil axle and
leaf-spring contact with paste Cramolyn or other
good contact lube. Be careful not to overtighten the screws
that are threaded into the ceramic.
Just finger-tight them and lock them in place with some
paint or fingernail polish. Seal the roller-bar screws
with paint as well. Now enjoy easy tuning.

On "chirp-" This is a classic MOPA rig. While you can expect
some small amount of chirp, I've got many transmitters in which
it is difficult to hear any at all. I've never had one that,
after I finished restoring it, had what I call "bad" chirp.
Noticeable chirp in an "ARC-5" transmitter
can usually be traced to a few sources.
Here they are in order of their usual appearance:

1. Poor power supply regulation.
Your supply needs guts enough to maintain 500-600 VDC at 200 mils
and 24 VDC at about 2.5 amps.
(if you don't want to use DC on the fils, put a diode and
filter cap at the relay)

2. Leaky bathtub caps. Reduces osc. drive, messes with
Osc B+, reduces grid bias to the 1625s. See above.

3. Cruddy output tuning network or antenna connections.
Anything that changes the loading- like heating the crud
between the roller and coil-
is going to pull the freq of an MOPA rig.

3. Low under-load emission in the 1626 Osc.
Swap it out with a known-good one.

4. Grid emission in one or both 1625s. Especially
noticeable in one that's been run at 800+ volts.
Swap with known good ones.

I've seen changed resistor values in the osc. stage
and misc. other stuff, but these four are the usual bandits.
While I've heard of the other mica caps going bad, I've
worked on many dozens and never seen it happen. I've
also never seen that custom "button" cap in the MO stage go bad.

I hope this will help out.
Next post for the power supply.

73 DE Dave Stinson AB5S
------
On an ARC-5 Power Supply:

First- there are three "flavors" of transmitters commonly
lumped under the name "ARC-5"
The first is the Navy ATA, second is the Army SCR-274N
and last is the Navy AN/ARC-5.
The rear connectors and wiring for the ATA and SCR-274N
rigs are identical. The AN/ARC-5 connector is
physically different and the wiring is also somewhat different.
If your transmitter is black wrinkle painted and
has a big RF choke next to the tank coil, it's
AN/ARC-5. If it's black and has not such coil,
but has an anchor in yellow paint on the back skirt,
it's an ATA. If it's silver, it's a later SCR-274N.
If it's black, has no RF Choke and has a "BC-4xx"
number on the back skirt, it's SCR-274N.

Transmitter Plug Pin-out:
(Note: If yours has an octal socket or anything
other then the 7-pin Mica connector,
then it's a modification and all bets are off.)

For AN/ARC-5-
There are seven pins. The pin in the center is
pin #7. Locate the pin that is grounded
to the chassis. This is pin #4.
Count the others *clockwise* around accordingly.

1. No Connection
2. +200VDC for the Osc. (needs to be right for stability).
3. Keying Relay (ground to key).
4. Ground.
5. A+ 24-28 VDC.
6. PA Screen Voltage (use 20K 5W dropping res. from B+).
7. PA Plate B+ Voltage +550VDC

For ATA/ARA and SCR-274N:
There are seven pins.
The pin in the center is pin #7.
Locate the pin that is grounded
to the chassis. This is pin #1.
Count the others *clockwise* around accordingly.

1. Ground
2. Test point for PA grid current.
3. +200VDC for the Osc. (needs to be right for stability).
4. PA Screen Voltage (use 20K 5W dropping res. from B+).
5. Keying Relay (ground to key).
6. A+ 24 VDC.
7. PA Plate B+ Voltage +550VDC.

The best way to get power to the rig is the way the
original engineers intended. I don't mean a dynamotor-
I mean a good, solid 550 VDC source and a divider.
Both the AN/ARC-5 and SCR-274N units derive their voltages
using a voltage divider network. We'll draw a divider that
matches the one used in the original power supply.
I very much recommend it.

Primary power should be 24-28 VDC at about 2.5 amps for relay
and filiments and B+ of 500-600 VDC at about 200 MA.
We will assume the designer's specs of
550 VDC B+ and 26 VDC filiment.
Get a pencil and a piece of paper. Follow along:

Place a dot on your paper and call that point "A".

Draw a line right to point "B".
From point "B", draw a line down and

connect a 20 K-ohm, 5 watt resistor here.
Call the other end of this resistor point "C".

Draw a line right from point "B" to point "D".

From "D", draw a line downward
and connect a 15 K-ohm, 10 watt resistor.
Call the other end of this resistor point "E".

From point "E", connect a 100 K-ohm 1 watt resistor to ground.

Draw a line right from point "D" to point "F".
Draw a line right from point "E" to point "H".

+550 VDC in at point "A".
+550 VDC out to PA plates at point "F".
+270 VDC out to PA screens at point "C".
+200 VDC out to Oscillator at point "H".

Bypass all outputs with about .01 ufd to ground.

If you wish to regulate the screens for AM,
connect an 0D3 VR tube with a .5 ufd at 300VDC
cap across it between point "C" and ground.
This will bring the screen down to 150 volts.

If you use this network, and use correct antenna
matching, you will be able to properly load and
tune your command set transmitter to rated output.

Voltages lower then 550 VDC will work just fine
with the same network. Voltages much higher will
cause MO drift and increase chirp.

----------------------

Antenna matching:

The "ARC-5" transmitter is not designed for a 50-ohm
antenna. It is designed for a 5-12 ohm aircraft antenna.
Doing it the "ham" way- turning the loading coil
to zero and the coupling to max- makes harmonic
rejection ineffective and does not allow maximum out.
To feed a 50-ohm antenna on 40 meters, the best thing
to do is to put a 200-pf variable cap between
the antenna post and your coax center conductor
(If you're using a "random wire," it will feed it if
it isn't close to a multiple of a 1/4 wave.
p.s. A "random wire" is a really lousy antenna).

If you don't have a good 200 pFd variable,
to get "in the ball park," insert a fixed 50 pF,
1000 Volt or better NP0 (no thermal drift) capacitor
and tune up- you'll use about a quarter to a third
of the roller coil and the link will be between
40 and 75 percent, depending on the exact model
of your transmitter. Vary the value up or down
to get best power out.
Clean that roller coil and tuning will be
much easier.

GL OM DE Dave Stinson AB5S

Bill M wrote in message
...
Michael Black wrote:


But wouldn't that have been because the US Novice license didn't allow
the use of VFOs until 1972?

Micahel VE2BVW


Ssshhhh!
Actually its kind of funny. As you know the dial readout on the ARC5 is
fairly precise and easy to read. I was very paranoid about using the
VFO and only used about 5 particular favorite frequencies for fear that
"they" would hear me all over the band.
Seems so silly nowadays with CBers raising havoc scot-free from 24-29 Mhz!

-Bill

Yea... those were also the days when we kept a logbook as per FCC
regulations---always in fear of the federal boys showing up and asking to
see it and check out the station.

I used a VFO too, Ranger I. Then again, my first transmitter was a single
tube 50C5 on a piece of plywood and one rock.

RG

I used an ARC5, converted to a MOPA with a 6AG7
oscillator, and yes, I built it myself. That
was my Novice transmitter, 40 watts to a 40 m
dipole.

Then, got an old ART-13 right after I passed the
General and used it as Novice rig. That VFO was
rock stable and never shut it off. Thought I'd
died and gone to heaven........Wow, 75 watts and
a VFO too!

73

Doug, K7YD