QRP AM transmitters

[VE3LYX]

I want to hear some PW Am transmitters on the air. I am becoming more and more convinced you need a decent amount of stomp with AM. What would be fine for CW seems pointeless on AM. Prove my idea wrong. I know , I have read them all. Worked four states the first night I fired up my 100mw am rig" Or 5 watt for that matter. I am thinking they must live at 4 Corners UTAH of for VE VA types Antigonish NS. So I would like to be proven wrong. I will be monitoring 3705 this weekend as much as possible. And I will have my 5 watts warmed up and ready to rip. I looked at old specs of HF military rigs. Distance for 6 watts on one was listed as 6 miles.  I am thinking I need probably 25 watts out to get out of my county even other then the odd lucky propagation day.. If I am wrong , good. I want to hear the PW / QRP rigs etc.
Don VE3LYX

[W4AAB]

I was looking through my old radio magazines the other day, and saw an article in February, 1956 CQ, of a 160 meter transmitter using a 6AG7 VFO driving a 6146, which is screen modulated by a 6L6. I would imagine it is more than QRP, maybe 25 to 30 watts out. There is a 9-watt 160m rig in one of the 1962 73 Magazines. I will look it up later.
                                     Joe W4AAB

[kb3ouk]

going by what the rules for the AM QRP net are, 807 power and less is considered QRP to most people.

[VK7ZL]

My homebrew QRP AM transmitter runs a QQV03/10 in the final with an output of 7 watts. About 12 months ago I used to regularly work station about 350 miles away on 7.125Mhz using a dipole antenna but conditions have deteriorated a bit since then.

[W4AAB]

The tube you mentioned is known as a 6360 here. I have a 2m and 220mHz transmitters by Tecraft that use them at around 10 watts out.

[VE3LYX]

I have 2 AM rigs using 6L6 PAs. One is not quite finished. I am waiting for some variable caps to come in the mail. The other is operational and while I have had a QSo with it it lacked stomp.  it shows as high as 9 watts out on the meter but the average on 80 is just over 5. I have monitored it with a portable set and it is very good a mile away from the QTH but at 5 to 6 miles cannot be heard. I dont know if this is because of 80 M propagation or the lack of power but I suspect the first as I had my brotherSWL about 6 ,ilesaway and he heard nthong. I then switched to my TS830S on the same antenna and he could not hear it either. I have worked Tim in Hanover but it was hard for him to hear me. More carrier then modulation but we did pulll it off. I dont care about dx especially. I just want a useable radio. I also want to know f it just me and my rig. So If I heard a PW or QRP Am set hee from anywhere really on AM I would know it is just me. I live in a AM desert I think. it seems to me that local Ham radio consisits of auto tuners . solid state riceboxes and in fact mostly 2 meter repeater operation (something I have absolutley no interest in whatsoever) so i have no-one who can give me a hand checking it out. locally. If I heard a 5 watter or even 10 watter from say across the lake. (Rochestor NY) I would be inspired to push further but all I hear are Dx 40s or Dx 60s or Valiants running into a Dentron amp at 400 to 800 watts. I keep thinking that if I can make an honest 25 watts out that would get me in the game at least but I am new to AM . It was gone when I licensed (1980). It is however what got me interested in Ham radio in the first place. So that is why I would like to hear some rigs on air of lower power. To get an idea of what is a practical level of power to shoot for. 5 isnt doing it for me except on an exceptional day. Maybe 15 or 20 would. I dont know.
VKs explanation of his activity seemed right to me. Sometimes it works but not in off conditions. And of course a SKed always works better then a cold call. Nothing worse then hearing. "I heard someone in there, did you Roy? " ----"Yeah I did but I dont recognize his call." Thats when you know you are wasting time.
Don Ve3LYX

[kb3ouk]

I would try improving your antenna before building something higher powered. the reason why you can't hear your signal 5 or 6 miles away is because it you are using a horizontal dipole, most of your groundwave is being absorbed by the ground, and unless you have a really low antenna, like for NVIS work, you aren't gonna hear any skywave. also, what are you using for a modulator? you might have better luck with the lower power if you add some more audio to your signal. don't stop at 100% modulation, aim for something more like 150% to 200% positive peaks, but don't allow the negative peaks to go past 100%. that way your signal will have nice loud audio even if you are only running 5 watts. and are you running 1 6L6 or a pair? according to the data sheet i have (found in the back of the 1953 ARRL handbook), a single 6L6 or 6L6G should be good for 11 watts with 325 volts 65 ma on the plate and 250 on the screen and -70 volt bias. a 6L6GX should do 20 watts with 325 volt 90 ma plate, 225 volt screen and -45 volt bias. also the drive power given is 250 mw. the 6L6 or 6L6G will have an input of 21 watts running under those conditions. for modulation, a pair of 6L6's running push pull AB2 will give 47 watts of audio with 360 volts 205 ma max signal plate, 270 volts 16 ma max signal screen, and -22.5 volt bias. load resistance is 3800 ohms. use some kind of negative peak limiter, like this one: http://classeradio.com/3-diode.jpg to keep the negative peaks from going over 100%. also, i recall seeing somewhere that it is beneficial if the keep alive power supply is not regulated, that way the voltage will sag a little bit. if it wouldn't have that room to sag, it would flatten out the negative peaks, so not regulating the keep alive voltage allows the negative peaks to be smoothed out but not go over 100%.

[VE3LYX]

Actually I am using an inverted L.. I use it often with my 50L6 Cw rig and it does a great job.I can make it to the east coast  and south to NC . That is a single tube (Bare Essentials Transmitter , pop electronics  but I used a 50L6 instead of a 50c5)  I should have checked to see if it can be heard at my pals site .
I do not think it is the best antena but it has done a great job for me here.  I have a single 6L6. one rig it is being driven by a 6v6 and the other by a 6ag7. The rig is screen modulated.  The other is sort of my own concoction. But I think if I read correctly aside from antenna improvements you also think it isnt a lot of power for practical use. Easiest fix for me would be a parallel pair of 6l6s Push pull is not an option right now as I cant come up with the necesary variable caps. I have had the 6l6 up in voltage and power did rise. They will take over 500 B+ without a whimper. I hurt that PS though so it is "in the garage" for repair. Currently I am running it at 380 working.voltage. (not idling) I will look into pushing the audio up a bit. I think that has posibilties. I do have a monitor scope. homebuilt I built about 20 years ago. It still works.
Anyway I have had the rx on 3705 all day. Heard a qso about 11 this morng. tried to tailend it but no joy. Other than that it is totaly quiet on the band. RX is on right now beside me. The tube specs are all good. I have looked athem a hundred times too but I wanna actually hear one of the PW rigs (cakepan special. 50c5 tx etc etcor even a barefoot DX35) on the air here. So far , no luck so I am believing they dont get out any better then mine. .
Don VE3LYX

[kb3ouk]

i've ran between 10 to 15 watts and got out ok with it. i think the best thing for you to try is increase your audio and experiment with some other antennas. paralleling the 6L6's together should work fine. I'd be curious to see if switching to a horizontal antenna, (compared to the inverted L, which is actually a type of vertical), might make a difference, especially for close-in work. once, i used a 200+ foot piece of wire that was badly matched to my rig and only fed 25 watts into it and got out about 200 miles, and that was on 160 meters. that wire was only about 25 feet off the ground in the highest spot, everywhere else it was 10 to 15 feet or less off the ground. my 75 meter dipole is 20 feet high, and it does good, even with low power.

[VE3LYX]

I have an inverted V on 40M but it has a short in the coax. Yes to all but just so you know how I think. If my 50l6 CW tx get out just fine on the same antenna and it couldnt possibly be even 10 watts then I had thought if I could get say a real 10 watts on AM out it might do it but now I am thinking 10 watts CW = 40 watts AM.
With the 50l6 CW rig my distance was 567miles as the crow flies. And the RST report was very good. I would like a 200 foot wire and 15 years ago it would have happened. Now just walking 200 feet is a chore. however I havenot dismissed the idea.
Don VE3LYX

[W6TOM]

  I have a GRC-9,( luggable) portable late WWII designed HF radio, on 80 meters I have an output of 5 watts carrier. On that band with good conditions I have worked a station in  Glendale, Ca (near LA) and another almost on the border with Mexico. We all were running GRC-9 radios, I have a 80M dipole, the station in Glendale had  an end fed wire and the other station a dipole. I'm in the Bay Area so furthest distance was around 425 miles.

 On 40 meters with the same radio but with much less power, output on 40 is 2 or 3 watts, I can work into Nevada and up to Oregon near Eugene, a 450 mile path.

 It's fun to see what this old set can do under good conditions, this radio was intended for short distances.

[W4AAB]

I am going to try using a 12BH7 as an oscillator. One triode section as the oscillator and the other as a buffer driving a 1625.The 12BH7 is used in a lot of the older CB sets as oscillator/tripler(from 9 mHz crystals). If anyone has used a 12BH7 in such a manner, I would appreciate any details.I first thought about a 12BY7 as the oscillator, but don't have one in my junkbox. I have several 35L6 and 50L6 tubes.Just trying to use the 9-pin sicket on the small chassis that I have.
                                                       Joe W4AAB

[W1RKW]

Well, I'm running a hot-rodded Small Wonder Labs Retro 75 as a PW rig.  I have modified it to have a wider frequency response and have bumped up the outpoot to 18 watts using a solid-state leenyar arrangement. Stock, the Retro has about 2 watts output. The audio mods provide more than 100% modulation and a fair low end. Stock, the modulation is about 70% and SSB quality.   I have received some good audio and readability reports, even from Mr. HLR.  So yes, you're right, audio level is the key.  

[W4AAB]

I heard Gary, K4XK running one of the Retro 75's the other night, and it had very good audio. What transistors did you use in the amp to give you 18 watts?
                                                       Joe W4AAB
                                             

[AF9J]

Bummer!  From posts I've read in this thread, it sounds like the Knight T-60 I picked up stupid cheap at a local hamfest ($25), is neither fish nore fowl.  Too much power for whatever AM PW nets are are cropping up, but not enough oomph (unless I run a linear - sorry, not happening! [besides, I have a Viking II]) for the regualr AM operating!   

[W1RKW]

I heard Gary, K4XK running one of the Retro 75's the other night, and it had very good audio. What transistors did you use in the amp to give you 18 watts?
                                                       Joe W4AAB
                                             

Joe,
A pair of MRF454s.  The amp is a Communications Concept EB63, heavily modified as well.

[w5rkl]

This may not fall into the same category since it doesn't take much power on 10 when the band is open. I run a modified 11 meter Johnson Messenger One at 7 watts output, crystal control on 29.0 AM, and have worked into New York, Florida, Washington State, Oregon, and California. Signal reports vary between S2 and S9+10. The antenna is a 102' long G5RV up 30 feet fed through a Drake MN-2000 tuner. I do not use any audio processing, the audio stage has not been modified, and the microphone is the factory hand microphone.

I recently modified a Johnson Messenger 223, VFO control at 6 watts on AM, but haven't worked anyone with it, band conditions have not been very good lately.

I'm sure when I put up a yagi antenna this spring/summer I will be working a lot more stations using low power than I am now.

73s
Mike
W5RKL

[Todd, KA1KAQ]

I am becoming more and more convinced you need a decent amount of stomp with AM.

You'd be right. At least on the low bands. During daytime hours you could likely make some local contacts, provided you have the flexibility to move around the band to find them. Keep in mind that your output power is going into two sidebands as well as a carrier. Not the most efficient means of QRP operation. Not impossible, just not as likely. 50-100 watts at night is possible on 80, though easily taken out by static crashes at distance.

Ten meters is another matter. Folks routinely work great distances with a few watts when the band is open. Numerous old CB radios running under ten watts have been converted and used this way. But even on ten, the 100 watt level seems to work more reliably. At least your chances are a lot better there.

The good news is, you get to choose: move to a band and/or equipment to make it happen, or sit on one 80m frequency with low power and hope for it to happen. One has a far higher likelihood of success. If you're wanting to try out your old rig, the common approach is to join or gather a group using another rig they can easily hear, then ask them to listen while you try the other rig. That way you have a captive audience and also a fallback should the old rig not be heard.

[ve6pg]

..don...there are guys around you, that will hear your qrp...al, ve3ajm is in bethany, and no noise level...eddie, ve3cui is a home builder...and i did hear you on 7120...can you try 3725, in the morning?...9am...i receive very well here...most mornings, weekday, and weekend try 3725 at 9am..where are you getting your parts from?..

..tim..

[W4AAB]

I just found a 12BY7. I will use it to drive the 1625, and save the 12BH7 for something else. Seems like that there was an article in a 1962 or 1963 CQ about a 6m AM transmitter using a 12BH7.
                                           Joe W4AAB

[WB2EMS]

I think it's really dependent on antennas and conditions. I've made contacts with an FT817 on an HF6 butternut, that's 5 watts PEP, 1.25 watts carrier - and that was from Ithaca in CNY to W1IA in deerfield NH as well as others. On the AM transmitter rally two years ago, I ran an ICOM 703 with 2.5 watts carrier into a ZB6BKW doublet at 20 feet and worked a dozen stations in a half hour - everyone I heard and called heard me.On other occasions I've been able to make contacts on 75 with that setup nearly every time I try.

On ten meters I've operated the 703 portable with a buddistick whip antenna and had a pipeline into Arizona one afternoon, working station after station on AM as well as other stations whenever the band is open.

There are a bunch of folks who built retro 75 rigs that run only a couple of watts of carrier and they are making regular contacts with them.

You should be able to make regular contacts with that power level. You're less than 2 S units below a 100 watt rig. I think I would see if you have some sort of issue with your antenna, it seems you should be able to do better than you are reporting.

Ellen, I'd love to find a T-60 like that. It was my first phone rig, running on 75 meters with an Eico VFO, and up on 10 and 6 meters with my buddy using crystals. You should be able to make contacts with it with no problem.
 

[AF9J]

I think it's really dependent on antennas and conditions. I've made contacts with an FT817 on an HF6 butternut, that's 5 watts PEP, 1.25 watts carrier - and that was from Ithaca in CNY to W1IA in deerfield NH as well as others. On the AM transmitter rally two years ago, I ran an ICOM 703 with 2.5 watts carrier into a ZB6BKW doublet at 20 feet and worked a dozen stations in a half hour - everyone I heard and called heard me.On other occasions I've been able to make contacts on 75 with that setup nearly every time I try.

On ten meters I've operated the 703 portable with a buddistick whip antenna and had a pipeline into Arizona one afternoon, working station after station on AM as well as other stations whenever the band is open.

There are a bunch of folks who built retro 75 rigs that run only a couple of watts of carrier and they are making regular contacts with them.

You should be able to make regular contacts with that power level. You're less than 2 S units below a 100 watt rig. I think I would see if you have some sort of issue with your antenna, it seems you should be able to do better than you are reporting.

Ellen, I'd love to find a T-60 like that. It was my first phone rig, running on 75 meters with an Eico VFO, and up on 10 and 6 meters with my buddy using crystals. You should be able to make contacts with it with no problem.
 

Yep. I have to decide if I want to just buy crystals at hamfests for the T-60, or throw a VFO on it.  I got it mainly for old school, semi-glowbug CW (sort of a nostalgia trip back to when I operated an HW-16 as a Novice), but it would be fun to try it on AM (even if some people say it's audio isn't the greatest).

[WQ9E]

I have heard a couple of T-60 transmitters on the air that sounded fine.  The major complaint I have heard about the T-60 is instability but I bet that traces back to the quality of original construction.   I have one paired with a KnightKit  R-195 receiver (solid state but the style matches the T-60 pretty well) and I mostly use it for CW but it has been on AM a few times.  Pierre K9EYE used to run a T-60 a lot on the MWCRN pre-net and it always sounded good.  I don't know if he uses it much anymore but several years ago I built a crystal switching box so he could easily change frequencies without having someone "see" for him what crystal was selected.

Ellen, I know you don't want to use an amp given space (and RFI) constraints but for others considering the T-60 (or other similar small rigs) they work wonderfully with some of the compact SSB oriented linear amps.  Controlled carrier is much easier on the tubes and power supplies of these lightweight amps and the combination provides for a decent AM signal with a low overall price.

[DMOD]

Would my HT-37 count as a QRP rig?   

Phil - AAC0OB

[WQ9E]

Would my HT-37 count as a QRP rig?   

Phil - AAC0OB

Only if the power transformer goes out    If you haven't done so already, go to solid state rectifiers and get the B+ and HV off the respective 5 volt windings.  This is the usual failure point for HT-37 (also HT-32) power transformers.