ARC-5 works great on AM...

[WB3JOK]

Decided to do something less strenuous this afternoon (after yesterday chucking 5500 lb of firewood down my cellar hatch, and splitting about 1/4 of it with a hydraulic log splitter, and replacing the washing machine water valve this morning), so made the typical ham modification to my 40m Command Set receiver. This was a very common mod back in the day, but some were not done so neatly if I do say so myself 
Controls are the usual gain, BFO switch and phone jack and I added a 2nd IF regen pot.

There were a couple of big AM signals up near 7290 a few minutes ago... don't remember the callsigns but I bet they're AMFoners 

The "ARC-5" receivers seem to work very well for listening to those who strap on AM. Lower down the band the very wide IF makes it tough to listen to just one QSO at a time especially with the KW's blasting in from 5-land. If I could find an affordable source of 2830 KHz crystals I might add a crystal filter since it has good sensitivity and excellent stability...

Anyway it looks neat sitting there 

-Charles

[KA0HCP]

Looks good!   So far I"ve managed to avoid accumulating any ARC-5 gear....yet. 

In the last several months there have been good discussions about homebrewing Q-multipliers and adding them to radios.  One, maybe two tubes and at most a dozen components. 

It's pretty simple.  Basically you add a regenerative function to the the IF stage.

I'll see if I can find a reference.

bill

[KA0HCP]

"Using the Q-Multiplier with Military Receivers" Donald Stoner, CQ Magazine, Feb. 1957.


http://www.antiqueradios.com/forums/viewtopic.php?t=96230
One discussion including comments from our 'very own W3JN"

[KA0HCP]

Here is a compilation of info on homebrewing a Q multiplier. I don't know the source to give credit.   b.

[Pete, WA2CWA]

Decided to do something less strenuous this afternoon (after yesterday chucking 5500 lb of firewood down my cellar hatch, and splitting about 1/4 of it with a hydraulic log splitter, and replacing the washing machine water valve this morning), so made the typical ham modification to my 40m Command Set receiver. This was a very common mod back in the day, but some were not done so neatly if I do say so myself 
Controls are the usual gain, BFO switch and phone jack and I added a 2nd IF regen pot.

There were a couple of big AM signals up near 7290 a few minutes ago... don't remember the callsigns but I bet they're AMFoners 

The "ARC-5" receivers seem to work very well for listening to those who strap on AM. Lower down the band the very wide IF makes it tough to listen to just one QSO at a time especially with the KW's blasting in from 5-land. If I could find an affordable source of 2830 KHz crystals I might add a crystal filter since it has good sensitivity and excellent stability...

Anyway it looks neat sitting there 

-Charles

I have an 80 meter version that was given to me several years ago. Actually sounds quite good but it is very broad. One Class E station transmitting and you think the tuning dial stopped working.

[WU2D]

ARC-5 receivers. Fun!

[KA0HCP]

In educating myself on the subject of add-on selectivity possibilities, a major challenge is modifying existing circuits to work with non-455khz IF's.

It appears the ARC-5 series radios used a number of different IF"s, and not being sure which your radio uses, it is impossible to provide an instant solution.

The other alternative is to use an Audio filter such as the National Select-O-Ject device introduced in the early 1950's.  It was offered both as an external box, and the circuit was incorporated in several National receivers.   

The manual and schematic are available at the BAMA Mirror archive.   bill

http://bama.edebris.com/manuals/national/s-o-ject/

[WB3JOK]

Sorry, I didn't explicitly state that this 7-9.1 MHz rx has the 2830 KHz IF... although those IF transformers have pretty decent Q, the BW is inevitably much greater than 3 KHz at that frequency.

The 3-6 MHz unit has a 1415 KHz IF so it can be tuned to be not quite so broad but given the crowding on 75m, ultimately no more useful. (I do have the 3-6 transmitter and a homebrew screen modulator. About 10W of PW carrier)  

I did install a plate-grid gimmick and a cathode pot (the 2nd IF regen mod that I alluded to). It helps some, but again, not enough in today's crowded bands.

An audio filter won't help (except for CW). Once the undesired signals have been detected, they are now in the audio passband along with the one you're trying to listen to. It really needs a narrower IF, and I am leaning toward a minimally invasive mod (like a crystal filter or perhaps a Q-multiplier if I can get it sharp enough) rather than redesign the entire innards.

Otherwise it ends up like my grandfather's axe... it has a new head, and a new handle, but it's my grandfather's axe  

Edit: searching for surplus crystals near 2.830 MHz... so far, only finding lots of cheap 2.4576 and 3.000 MHz xtals but not sure the IF cans (or the LO) can be tuned that much. $urplu$ $ale$ has 2.850 in the HC-6/U can for $4 each. That'll work but $20 for crystals. Yeah, I'm cheap

[WU2D]

Charles,

Check out the videos I did on the command receiver on Youtube. I compare the regen mod with a q-multiplier, and do the crystal filter mod you describe on a 40M.

https://www.youtube.com/watch?v=XlrPCR1IKlo

Good Luck! Mike

[WB3JOK]

Nice work! The Q-multiplier looks like it would do the job, but requires an outboard chassis and another knob to constantly diddle...

I'm impressed with how effective the (single) crystal filter was. The ARC-5's audio quality isn't anything to write home about anyway, nor am I trying to drive a good speaker, so I'm not too worried about it being a little narrow.

 I might just try it before building a 4- or 5-crystal Cohn (minimum loss) filter. You wouldn't happen to have a spare 2830 KHz crystal in the junkbox, would you?

[VE3LYX]

I have a AM Arc5 station. A Bc454for listening on 80M and a couple of transmitters , one I moved to 80m and one i moved to 160M. 160m in any mode has proved a waste of energy here however 80M has yielded several QSOs. Sometimes I hear my audio isn't this or that and is a bit light however I modulate them with a homebrew series cathode modulator (or sometimes the 56 ARRL so called simple grid modulator which even though it is inserted directly in series with the cathode and ground  (because it indirectly affects the grid they insist on calling it that even though a proper grid modulator it isn't) I don't use the rigs or the rx regularly but just for fun when conditions are good so I am happy just to be able to communicate and be understood with such a simple solution. The Rx does leave a bit to be desired but it does work and is stable so I just enjoy them for what they are. I am glad you are having fun with yours.
don

[WB3JOK]

I am always favorably impressed with the capability and performance in such a compact package (except for the selectivity). My first ARC-5 was also a 7-9.1 Mc brand-new unit I bought at the Gaithersburg MD hamfest in '78 for $5.00, and built a power supply onto the back deck. Wish I knew what happened to it...

Anyhow I emailed JAN Crystals and got a reply back (via Monique Whan at calebscrusade.com!) saying "sorry, we no longer manufacture crystals" so will see what ICM wants for a 2.830 MHz xtal.

[Pete, WA2CWA]

I am always favorably impressed with the capability and performance in such a compact package (except for the selectivity). My first ARC-5 was also a 7-9.1 Mc brand-new unit I bought at the Gaithersburg MD hamfest in '78 for $5.00, and built a power supply onto the back deck. Wish I knew what happened to it...

Anyhow I emailed JAN Crystals and got a reply back (via Monique Whan at calebscrusade.com!) saying "sorry, we no longer manufacture crystals" so will see what ICM wants for a 2.830 MHz xtal.

I have a 2830 KHz crystal if you still need it. Drop me a PM.

[WB3JOK]

Thanks Pete!  Much appreciated.

Today I modified the IF can per Mike WU2D's video. I used some Kapton tape for interwinding insulation since the remaining original primary has plate voltage on it. Now all I need is for the crystal to arrive!

Incidentally, to manufacture new 2.830 MHz crystals, ICM wants $36.25. Each. 

[Pete, WA2CWA]

If you believe USPS, it will be there Saturday.

[WB3JOK]

Surprisingly, it did arrive as scheduled. I put it in and fired up the rx. Smoke from under the chassis. Shit!  
Turned out I'd left a connected piece of (the original) bus wire in the IF can and hadn't cut it off and had shorted to ground, frying the 200 ohm resistor providing plate voltage to the mixer and RF stages.

Fixed that. Then it started to work but was deaf as a post. I was getting worried until I realized that a very sharp xtal filter at the input to the first IF would make realigning all three IF cans critical. Tuned them up to 2830.0 KHz but the modified can still wasn't peaking even at max trimmer capacitance. I added a 33 pf silver-mica across the 110 pf NPO cap (that replaced the original 180 pf can), found a peak. Sensitivity definitely better!

Then I adjusted the new crystal phasing trimmer to peak at 2828.5 KHz for LSB (Do I have that backwards? I'm assuming the LO is lower than the RF, not higher), and finally set the BFO for intelligible SSB signals.

Now it works but is still down on sensitivity somewhat (probably because the new IF transformer winding driving the crystal has far fewer turns than the original pie-wound coil). The background noise is quieter too, so perhaps it'd be easier to add some AF gain rather than IF? Is there a tube I can plug in to replace the 12A6 that'll have more gain?

Anyhow it's MUCH sharper now, requiring a delicate touch on the tuning knob, although (with just one crystal) the skirt selectivity isn't that great. But it's a big improvement from the stock (20 KHz?) BW and it's almost usable on 40m now - don't have to listen to that one W5 whether I want to or not  
It still works for listening to the AMers on 7290 also!

[WB3JOK]

40 meters just died tonight! I thought something was wrong with the receiver since I could only hear a couple of stations on my OCF dipole, whereas an hour or two ago the "Winter Field Day" contest was really crowding the band.

So I hooked it back up to my hp 8640B signal generator and re-tweaked the IF and the crystal phasing trimmer... everything OK. So I fired up the SB-102 and reconnected the dipole to it... STILL can't hear anybody. Amazing the bottom really fell out quick.  

On the subject of reduced sensitivity, I think some matching from the output of the crystal circuit (which is probably on the order of 1-2k ohms impedance) to the grid of the 1st IF stage (likely to be considerably higher Z) is required. I wonder if a tiny toroid (T37 size) unun, say 9:1, would be worth trying?

Edit: a little research shows that a FT50-43 toroid with 11 turns is 1000 ohms, so if I trifilar-wind some small (say, #32 AWG) wire on such a core, that'll be a better match and provide 3:1 voltage stepup too. That will fit in the IF can with ease.

[WB3JOK]

I wound an FT50-43 toroid with 12 turns of quadrifilar #32 as a 1:4 step-up. Checked to make sure it did work at 2.830 MHz and was wired correctly with my signal generator and HP 400D VTVM - (yep - 0.1 volts RMS in, 0.4 volts out), and tucked it into the IF can between the crystal filter and the output to the 1st IF grid. When retuning I noticed I was at max on the trimmer so I had to add another NPO capacitor.

The sensitivity is considerably improved (experimenting with various loading resistors on the transformer output looking for a better match to the crystal didn't seem to make much difference)... now I can hear quite a few more stations, so the modest skirt selectivity from one crystal is again at issue. It's much narrower than the 20+ KHz bandwidth as initially designed though. The broadcasters are really destroying 40m tonight as well as the alligators in 5-land... Anyhow I'm done trying to make a silk purse out of a sow's ear. It's as good as it's gonna get without major redesign

Besides, I also picked up a 40m transmitter, missing the tubes and cover for a couple of bucks; I have lots of 1625's in the junkbox and my homebrewed screen modulator, currently connected to the 80m transmitter. Maybe I'll get on the air with the PW'er soon

[VE3LYX]

Im good for an arc5 to arc5 80M anytime
don

[WB3JOK]

That'd be neat to have an all-ARC-5 QSO  Someday.

My receiver is powered as designed by 24-28 volts DC and the original dynamotor, too! The whirr will probably be heard in the mike. Transmitter supplied by the AC line, I don't have near enough 28 DC to run the big dynamotors (plus they are really noisy).

I don't have a 3-6 Mc. receiver (at the moment), and I'm waiting for a 1626 (oscillator tube) so I can get the 40m transmitter on the air. Wonder if I can reach VE-land on 10 watts of carrier?

[VE3LYX]

I only have 80M ARC5 with both Rx and TX. I have one tx  on 160M but never had a contact. I don't have a 40m (yet). If you use another RX on 80M I,ll never tell. We are only 281 miles apart so we should be able to pull it off on a good day. I have worked into Maine and Virginia with my one tubers on phone (300 to 400 miles) and they are less then 5 watts out. Early morning some weekends I used to hear some Hams on AM from out your way. Ie 7 to 8 AM EST. If your receiver can hear CHU time signal well (3330kcs) the propagation should be right for us at the same time. That is how I decide when to try . I check for CHU and WWV . If I can hear CHU I know east west is probably not bad  and if I can hear WWV North south is likely to be good. You are mostly west of me I think in a southerly direction if you know what I mean. IE more west then south. We could find each other on CW (full carrier) then switch to phone. I often use a set of VVV VVV VVV de ve3LYX as it is quick and easy for one to to pick out when hunting for another station.
don

[WB3JOK]

281 miles? I think your map is just a little "off"... that distance northeast is still in Missouri, and there are a few other states to traverse before reaching Ontario!  Or are you somewhere else...

I wasn't even looking for the 7-9.1 Mc receiver when I found this one - just stumbled across it at a flea market. I'm keeping an eye out for a 3-6 Mc. unit too. Not on ebay, those prices are outrageous and tend to be for carcasses "missing tubes and covers" and looking like a deuce & a half ran over them.

I haven't operated CW since the 70's (got my Novice in 1976). I doubt I could pass that test 

Meanwhile, cleaning up the 7-9.1 Mc transmitter. Although it looks like it may never have been used, someone dropped it on the right front corner of the panel and severely bent it. I straightened it as best I could (luckily the roller inductor was intact once its bearing support wires were realigned), put in a couple of 1625's, now waiting for the remaining two tubes to arrive.

Here's a pic of my 3-6 Mc. transmitter and screen modulator/power supply setup.

[VE3LYX]

That was from QRZ .com so your comment made me go back and look. They have your address in MO Howell Cty but on the map your antenna is in Pittburgh PA. That is a log feedline!  Ur right! Probably more like 600 miles. My antenna is about 30 miles north of where I live too on their map but I guess that is no real big deal. Can you give me another ham call in the area and I will check his details.   I am interested in how you made your screen modulator and would like to know more. Forget the CW then we can just holler. On a good day we might still do it.
don

[WB3JOK]

Weird! I just looked at my own entry on QRZ and those lat. & long. coordinates are completely wrong. I'm more like 36 deg N, not 40... Although I did live in Pittsburgh for 2 years while going to school there from '96-'98. Wonder if QRZ can fix that.

The screen mod is a simple design mostly lifted from mid-1960's ARRL Handbooks. A typical 12AX7 speech amp driving a 6AQ5 in class A, coupled (I think capacitively, will try and dig up the schematic) to the screens of the 1625's. The rest is just power supply, using a 480:120 volt control transformer wired backwards in the "economy" circuit, with VR tubes for oscillator regulated B+, and a hefty transformer/bridge/filter cap to supply 28 DC for filaments, receiver dynamotor, and relays. 

[VE3LYX]

My PS is thhe "economy" from the handbooks. I am familiar with your mod circuit. I have an earlier 50s version 6sl7 6v6 used a bit differently but in inch in more or less the same.
don