The AM Forum

How difficult would it be to adapt a BC-696/ARC-5 transmitter (3.0-4.0 MHz) to AM phone use? The original modulator/dynamotor units seem to be hard to find. Also, is there any information out there on how to build a power supply for these transmitters?

  You would need to make a modulator, the command sets used a separate modulator which from what I have seen is difficult to locate. The connectors are not easy to locate either. Then you would need a power supply and this was a  low power set too. I had actually thought of doing what you are thinking of and the difficulties just mentioned made me decide not to.

  A better choice would be an ART-13, this would give you a 100 to 150 watts of carrier. This was also an aviation set made to run off a dynamotor. I have several and run them off a dynamotor but building a power supply isn't to difficult.

  Henry Rogers, WA7YBS, has some good ifo on his website about the ART-13, you might take a look at that. HTH......

 

Only problem is, I already have the BC-696, and am on a tight budget. Unless you can find me an ART-13 for $50 or less (I paid $45 for the BC-696), it's just not feasible. At least if I have to build a modulator and power supply (which is what I figured I would have to do), I can spread the cost out over time. What I was wondering is if there was information available that would tell me HOW to build a modulator and power supply SPECIFICALLY for the BC-696.

An inexpensive and easy way to build a modulator can be done using this link:

http://www.amwindow.org/tech/htm/modheising.htm (http://www.amwindow.org/tech/htm/modheising.htm)

Instead of using the modulation transformer, you could backwards feed an 8 ohm audio transformer with a regular PA amp.  I've done this with a transmitter before and it worked great.  Use the high-impedance side of the transformer to feed the Heising circuit on the right. 

Plus, the modulator would be all solid state.

Jon
KA1TDQ

You might want to have a look here:https://groups.yahoo.com/neo/groups/ARC-5radio/files
A lot of good info for the SCR274N sets.
The BC-696 was originally designed to be screen modulated. If your has the original power connector on the back you make a socket to fit it using molex pins and bondo.
Most of those old guys need a good cleaning to get them the operate well, good stable output.

GL
Terry N3GTE

  I have been plate modulating myarc5 transmitters using a series modulator  I built 6 years ago .  The article and schematic are located
here : http://amfone.net/Amforum/index.php?topic=27856.msg212690#msg212690.
 It uses hi voltage power mosfets which  are still available  relatively cheap . When powering the arc5's ,
 you need to regulate the oscillator b+ to around 210 volts . I'm using a string of 5 watt zeners  for this. The pot for adjusting 
the modulated b+ can set to a range of voltages .I found 450 volts is good value for head room and isn't too hard on the 1625's.
 Typically get 40 watts of rf output with my sets using this modulator . I have checked in to the old military radio net on 3885
Saturday mornings with my BC457 and this modulator getting good reports.
73's Bob W1FYO

Are you using separate power supplies for the modulator and the ARC-5? Do you have schematics for your PSU's? I have the 1959 and 1961 issues of the ARRL Handbook, but neither one has anything about converting/adapting surplus equipment. Surprised me, since that was arounf the time when they were fairly popular, I think.

QST ran several articles on the ARC-5 back in the 50's. However, your best bet would be CQ Magazine which ran tons of articles on surplus equipment and even created 2 or 3 surplus equipment handbooks.

I downloaded the manuals, but didn't find them to be very helpful. In fact, the only thing I found for the BC-696 was on how to convert it into a rather low-power linear amplifier. Are the old CQ magazines available for download?

To be honest, I tend to do best on projects of this nature when I have a parts list, a good schematic, and a detailed set of step-by-step instructions ("Cut wire 'a'. Solder jumper wire from lug 'b' to socket 'c'", etc.). Maybe I am being unrealistic...?

Like QST, CQ Magazine is covered by Copyright. CQ has authorized HamCall ( http://hamcall.net/cqcgi ) to provide downloads on a subscription basis.


On lots of this old stuff, you sometimes have to wing it with just piecemeal information.

Pete,

Any idea which CQ magazine this info is in?  I have some old CQs, I might have the one he needs.

Fred

Check this link out for conversion info. a lot of useful info.

www.w7ekb.com/glowbugs/Military/PDF%20files/.../command_sets.PDF

My approach is is different from the above . Back in the fifties silicon power rectifiers were not well known or available.
So hams had to rewire the filaments for 12.6 vac a, a common practice. My psu runs 25 vdc to the filaments and control relay.
No rewiring necessary. I think the command sets  were intended to be screen modulated so plate modulation may be a little stressful.
I had to replace the 20 ohm series resistor/fuse to the tank circuit which blew out on voice peaks. Not a problem with the arc5's which are shunt fed
B+ and have no series resistor.
Hope this helps.
73's Bob W1FYO   

Don't know if this is useful for your particular project, but there is a Dynamotor for sale on QTH.com.  Listing #1206638

Also have a look at Listing #1207284

Ken

Getting command sets on the air is about as difficult as building your own transmitter from scratch.  Unless you can get all the cables and ancillary equipment (next to impossible) you need to build your own power supply, t/r switching, and modulator.  You really need to want it.  Anything less is not going to make it.  If you want to be a home brewer, this is a good place to start, but step by step instructions aren't going to work, there is too much to learn.

I started my ham journey in 1964 as a 12 year old with an 80 meter AN/ARC-5.  I still have it and use it regularly on CW.  There is a project in an old 1958 (I think) QST for a cathode modulator that just plugs into the key jack that I tried when I got my General at 13 years old.  It have great sounding audio, but didn't put out much power.

I hope this information is helpful, good luck.

Best regards,
Chris W7FOX

Have no clue. Go here  http://hamcall.net/cqcgi and search the CQ Magazine archives for model, project, etc.

The 1964 ARRL handbook has a section in the High-Frequency Transmitter chapter titled "Converting Surplus Transmitters For Novice Use" beginning on page 217.  A power supply and crystal oscillator are shown as well as all the instructions for modifications.  It doesn't include a modulator, but adding one would be relatively simple once you decide on which type you want to use; screen, plate or cathode, etc.

I have the published for CQ mag "Surplus Conversion Handbook" here. There is an article on building a modulator for the ARC-5 transmitter. It uses a direct coupled cathode follower audio driver 6SN7, and a pair of 807 modulators in class B. It was all built on a stripped down SCR-274-N chassis. It doesn't show what the original CQ article this was from. There are some power supply projects there too to sub for the PE-103.

I can scan and send you the info/article if you're interested.

Al VE3AJM

Here's a good starting point to get the tx in good shape. I tend to shy away from the Surplus Conversion Manuals unless your is hacked up.

http://www.w7ekb.com/glowbugs/Military/DaveStinsonARC-5Article.pdf

Terry N3GTE

Yeah, it's been hacked, all right. 'Way back in 1948, in fact! A date in that year and the callsign of the ham who owned it (and presumably did the mods) was scratched on the inside of the bottom cover...

Can you tell from the photos if it is still a transmitter, or if it was modded into something else (like a VFO or amplifier)?

(http://i294.photobucket.com/albums/mm100/DutchmanDick/ham%20radio/DSC02947_zpsmyavvvju.jpg)

(http://i294.photobucket.com/albums/mm100/DutchmanDick/ham%20radio/DSC02946_zpsiuv02rw8.jpg)

(http://i294.photobucket.com/albums/mm100/DutchmanDick/ham%20radio/DSC02945_zpsaqyvkixg.jpg)

(http://i294.photobucket.com/albums/mm100/DutchmanDick/ham%20radio/DSC02944_zpsxpas5t6x.jpg)

(http://i294.photobucket.com/albums/mm100/DutchmanDick/ham%20radio/DSC02943_zpsvjupgeyw.jpg)

(http://i294.photobucket.com/albums/mm100/DutchmanDick/ham%20radio/DSC02942_zpsxyemlg60.jpg)

It has definitely been moded, and my guess would be a VFO.

The top of the chassis is missing the roller inductor and associated supports (for antenna matching) and the antenna relay.  The antenna connector is obviously not original.  The holes in the front panel look to be original, used to mount the roller inductor and relay.    The antenna coupler knob is toast, but the shaft and gear connection behind the panel looks OK.   You'll have to check the transformer and capacitors inside the top shield for modifications.

The under side of the chassis is missing the relay and associated wiring.  While you'd have to remove the obviously "new" components to reutrn it to a transmitter (mostly with new 1/2W resistors and bypass capacitors),  the underside looks to be pretty good otherwise.   I can't tell if the heaters have been rewired for a different voltage.  Simple enough to fix though.

The other plus is that the power rectipcle is stock.  The bad news is that stand alone male plugs are like hen's teeth to find.   The good news is that you can cheaply by pins to mate with the individual holes.  When I did my first ARC-5 restoration I used individual pins and made a small cable attached to a barrier strip, then off to the power supply.  Why a barrier strip?  So I could rewire the cable for either ARC-5 or SCR-274N transmitters.

As N3GTE pointed out, Dave's article is the way to go to answer your power questions.  Most of us run the power supply setup Dave recomments.  It's simply the same resistor network that is found in the modulator unit.  I think 3 or 4 resistors.    I have several ARC-5 transmitters and an SCR-274N system and the power supply schema works fine.   

Yes, you'll have to build an external modulator for AM.   

While the unit is very restorable, but I recommend you get the parts in hand first.  Get on the ARC-5 reflector and see what you can dig up.

That's the best I can do from memory here at the office......

73 Mark K3MSB

Entirely possible it was modded into a VFO. It came with a short cable with a connector that matches the one on the front panel at one and , and an RCA connector at the other end.

Since it has already been hacked, any harm in replacing the military socket with an octal? Or not a good idea? I have heard that was a common mod.

What exactly is the "Arc 5 reflector" you mentioned?

This ancient article shows how to convert the MD-7 modulator to ham use. Even if you don't have one, there is a working plan that makes 60W.

People have used an ARC transmitter chassis with the two beam power tube sockets and made up a modulator on it to match the rest of the sets. Purists may howl if you defile a restorable set though.. I think I have an MD-7 modulation transformer if you are really interested. It's a little smaller than the ART-13 one.

For the B+ supply, the original dynamotor DY-8 or DY-33 output spec is 575V@160mA cont., 540V@250mA intermittent.
A list of various dynamotor electrical specifications is also attached.

This link has more info on modulators and power for the command sets including a design for cathode follower drive of the modulator grids in the "special class B" arrangement:
http://www.w7ekb.com/glowbugs/Military/PDF%20files/ARC5/command_sets.PDF

I've been working with the guy to build a good PSU for that TX, send him some repair stuff for it, and set up a high-level plate modulator for it down the road. ;)

73DG

Ha!  Now there's a good question to start the internet version of a food fight!  ;D

Personally, I view your unit as restorable and would not remove the rear connector.  I'd try and restore it to stock configuration.  Note that's my opinion.

That being said,  it's your property so you have the right to do what you wish.   If you have no intention of restoring it, then yeah, get rid of the connector and go with an octal socket.


It's an email based newsgroup.  Very nice group of fellows dedicated to all things ARC-5 (and a lot of udder stuff too.....).

http://www.signalone.com/arc5/list/faq.html

Hi Dennis

At a fester in May I picked up an ARC-5 TX, SCR-274N RX, and HB PS with switching relay for the princely sum of $55.  The primary reasons I bought them were the original tuning knob on the receiver and the male plug (can it really be?) for the ARC-5 TX.   

The HB PS was a very nice construction job with meters etc, and it looked to be built onto an ARC-5 base.  I get the unit home and as I was putting it on the "pile" I noted it had about 6 tubes therein  Closer inspection showed a few extra transformers aside from the power transformer and filter choke.   I'm wondering if it's a PS and HB modulator / speech amplifier!    I started to take it apart and then stopped -- can't violate my "only one project at a time" rule.....   and I'm still working on the HQ-129-X !!     

Hi Rich

Looks like a VFO that you have. Heres some info that may help you reverse engineer that unit you have and return it to stock form. Hopefully you can find some complete units up there and some parts.

Al VE3AJM

Don't think it's been rewired for 12v. Most of the time the power resistor on the back wall is removed (126ohms). It balances the heater current between the 1626 and the 1629.
Here's a pic of the roller inductor: https://www.flickr.com/photos/53710524@N06/
Each different tx (band) uses a different roller so there is 4 or 5 common ones but you need the one for a ARC-5 T-19 or for the BC-696.
Don't really need the ant relay but selector relay (the one underneath) is pretty handy to use to key it.
Terry N3GTE

If you have already had a chance to take a look here's a great series on the BC/ARC tx's.

https://www.youtube.com/watch?v=x2IlIrYPTSM

Enjoy!

Terry N3GTE

Sorry wrong Filckr link. Here's the right one:  https://www.flickr.com/photos/53710524@N06/6716953139/in/dateposted/
Also you can see the ant relay and ant spring contact. Usually missing. I believe the pic is a BC-696. Note the roller and the turns on it just to give you an idea how many it has. The two odd band and the 40mtr tx have less turns. There is a part # on the end that verify which set it goes to.

Terry N3GTE

Pull a little reverse engineering on that job, keep us informed.

73DG

Another Dynamotor on QTH...http://swap.qth.com/view_ad.php?counter=1209278 (http://swap.qth.com/view_ad.php?counter=1209278)

The ad makes one think it is for free for the picking it up and hauling it away?

Ken

WAY too far away, unfortunately, for me to travel to get it - the gas costs (not to mention other travel expenses) would exceed the value of the power supply!

Yea I didn't know one way or the other if there were other means of retrieving it?  I thought I would just put it out there, one never knows...?

Ken
 

You may find some useful tips on this thread:
http://amfone.net/Amforum/index.php?topic=37682.0
 ;D
(Keep reading the whole thread, if you have the patience... after the receiver adventures, I started on the transmitter and amplifier).

Don't butcher up the filament wiring. It's not hard to come up with 24-28 volts if you're building a PS anyway...
I love my ARC-5's  8)
-Charles