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PostPosted: Sat Feb 07, 2009 7:04 pm 
I've gathered up all the parts I think I need to build one of these, but I have several questions I would like to ask before I start on this project (I'm not in a huge hurry here, I have six more weeks of classes before I take my test):

1. I have a 1956 ARRL book that has plans for one of these, but I've seen about a dozen different sets of plans on the internet. Can we discuss pros and cons of different ways this can be done.

2. My book calls for the final coil to be inside of a can. It gives a part number, but no real details about it. Most of the plans I see on the net do not have the coil in a can like this. So my question is... Does the coil need to be in a can, and if so should it be something ferris (steel) or should it be aluminum? And if so, how big should the can be? The picture in the book shows a can that's about twice as big around as the coil.

3. My book and most all the plans I've looked at show the key being on the cathode. How much voltage and current is going to be on the key? (I ask because I want to homebrew the key also).

4. I've seen one or maybe two sets of plans that also allow the same transmitter to also run on 15 and 10 meters. Is this a good idea? Does/can it work well?

5. Any hints or tips about this that I have not mentioned are welcome. :lol:


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PostPosted: Sat Feb 07, 2009 7:31 pm 
From growing up with a 6AG7 in one pocket and an 807 in the other, I think I can share a few things.

First of all, don't even contemplate running a single tube crystal controlled transmitter on 15 or 10 meters. It will simply make you very frustrated and you will want to turn to collecting postage stamps!

The 6AG7 was, in my opinion, the best crystal oscillator tube ever made! Using it in the Colpitts circuit, which the ARRL kept referring to as the "grid-plate" oscillator circuit is best. You can control the feedback easily with the trimmer capacitor in the cathode circuit and get a chirp free note from nearly any crystal worthy of its quartz.

Back in 1956, TVI was the main concern of hams and if things were not shielded, they should be bypassed to ground, and if that was not possible, then grounded. Luckily, those days are behind us now. I honestly can not remember all the transmitters in the 40 to 100 watt catagory I have built, especially in my younger years as a ham. Probably close to a hundred!

Back then I said the hell with the neighbors and built everything with the coils on top of the chassis standing up proudly. High and wide and proudly was the terms used. Shielding....what was that? Something the store bought radios had?

Yes, I did get complaints from the neighbors, as we are in a fringe channel 2 area, but still I stood my ground and operated as much as I could. I was somewhat of a radical back in the mid 1960's, to say the least!

I would foreget the shields around the coils and simply use good construction practices and if it is a one tube set, not much to worry about. It is when you get into multi-tube sets that you have to worry about feedback and such from the final to the intermediate stages and that requires mounting the coils under the chassis, or hiding them so that the final does not see them, but we will cross that bridge when we get there.

Good luck with your endeavors building a homebrew rig. I know it was sure a lot of fun for me.
Curt


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PostPosted: Sat Feb 07, 2009 7:56 pm 
Curt Reed wrote:
From growing up with a 6AG7 in one pocket and an 807 in the other, I think I can share a few things.


I was hoping you you would chime in, I'm SURE you can share a few things that I don't know. :wink:

Quote:
First of all, don't even contemplate running a single tube crystal controlled transmitter on 15 or 10 meters.


Thanks. I did see at least one set of plans for this, but I figured it was something easy there would have been more.

Quote:
The 6AG7 was, in my opinion, the best crystal oscillator tube ever made! Using it in the Colpitts circuit, which the ARRL kept referring to as the "grid-plate" oscillator circuit is best. You can control the feedback easily with the trimmer capacitor in the cathode circuit and get a chirp free note from nearly any crystal worthy of its quartz.


That's good to know. I have a couple of crystals I should be able to use on 80 meters. I will have to come up with some that are right to hit 40 meters.

Quote:
I would foreget the shields around the coils and simply use good construction practices and if it is a one tube set, not much to worry about.


Good enough. Now I understand why so many of the sets I see on the net didn't bother with shielding the coil.

Eventually I also want to build something for 10, 6, ans 2 meters, but the 6AG7/6L6 setup looks like a good place to start. It looks fairly easy to build and should still put out enough watts that it can be heard for a little distance.


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PostPosted: Sat Feb 07, 2009 7:57 pm 
Rereading your post says you plan to use a 6L6 in the final. I have never been comfortable with that tube. I would use an 807 instead. Basically the 6L6 is a single ended tube and it is hard to isolate the input from the output. I guess that if you were careful in layout, you could do good with one, but with the 807 being a double ended tube, you could put the grid circuitry under the chassis and keep the plate circuitry on the top of the chassis, so the final will not decide to "take off" on its own accord. Use a metal 6L6 and make sure pin 1 of it is grounded to the chassis with the shortest possible leads.

You could probably expect up to 100 volts across the key in a cathode keyed circuit like that. Nothing too dangerous, but it is noticable if you get across the key contacts when the key is open. Back when I started, my first key was a J-38 clone and I soon ventured into the world of bugs and had a Vibroplex Lightning Bug for many years. I kept burning up the contacts keying my military surplus rigs like the AN/ARC-2 transceiver I had, as it keyed several relays in the 28 volt circuit and the inductive kick from all those relays was murder on bug contacts!

Later I went to using a keyer, and I can no longer control a bug after becomming good with a keyer. Right before I became inactive, I was heavily involved in milsurp rigs again and I would dig out the old enclosed Navy Flameproof key to key them, as the Bencher would not handle the inductive loads they present.
Curt


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PostPosted: Sat Feb 07, 2009 8:06 pm 
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Hey Microbes,

Care to share that schematic?

Gus

_________________
Old age is 'when you still have
something on the ball, but you are just too tired to bounce it.'


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PostPosted: Sat Feb 07, 2009 9:38 pm 
I dug out my 1956 Handbook and was some what surprized to see that this rig does not use the Colpitts oscillator. It uses the Pierce oscillator circuit with the screen of the 6AG7 serving as the plate. As a result, both sides of the crystal are "hot".

If you are wanting to build a two stage transmitter, a much better design follows it on page 175, which is called "A Novice Transmitter for 7 and 21 Mc." It uses the Colpitts oscillator I mentioned and has the plate of the tube tuned to control the drive to the final. Of course the tube lineup is different, but the 6AG7 would work just as well as the 6CL6 in that design. Surprizing that they did not make it also include the 80 meter band, but back then, I think 40 was the hot band of choice for most novices. You could wind the coils to resonate on 80 meters without any problems and it would work just fine on 80.
Curt


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PostPosted: Sat Feb 07, 2009 10:05 pm 
gusnaz wrote:
Hey Microbes,

Care to share that schematic?


No problem, this is the one out of my book (I think it's readable):

Image

Like I said, there are at least a dozen variations of this on the net. google link: here . Mostly the differences have to do with the final coil and cap(s) and/or the pilot light (some don't use it at all, some replace it with a 150 ma. meter. My book says use the light OR a meter).

Curt Reed wrote:
Rereading your post says you plan to use a 6L6 in the final.


Well.... I DO have plans for a single tube unit using the 6AG7, but they say it only puts out ~ 7 watts, and this is suppose to put out 35 watts. It doesn't look like it's much harder to build, and I thought it would get me more distance than 7 watts would. Is this a mistake?

Quote:
Use a metal 6L6 and make sure pin 1 of it is grounded to the chassis with the shortest possible leads.


The plans say to ground pin one with a short lead. Why a metal tube instead of a glass one? (the pictures in my book do show a metal tube, but many of the ones on the net do not). I will have to look thru all my metal tubes, I know I have some glass 6L6 tubes but I'm sure about metal ones.

Quote:
You could probably expect up to 100 volts across the key in a cathode keyed circuit like that. Nothing too dangerous, but it is noticable if you get across the key contacts when the key is open.


Is there a reason that a relay couldn't be used between the key and the 100 volts?


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PostPosted: Sat Feb 07, 2009 10:37 pm 
Curt Reed wrote:
If you are wanting to build a two stage transmitter, a much better design follows it on page 175, which is called "A Novice Transmitter for 7 and 21 Mc." It uses the Colpitts oscillator I mentioned and has the plate of the tube tuned to control the drive to the final. Of course the tube lineup is different, but the 6AG7 would work just as well as the 6CL6 in that design.


Ok, I'm looking at it. It's a little more complex, but not much. I take it that your warning about 15 meters on a single tube set doesn't apply here?

I think I read somewhere that the 6AG7 has the same specs as the 6CL6 except that the 6CL6 is a miniature, so that would work.

I'm not sure i have a 6BQ6 (I will have to check), is there anything that could be sub'ed for it without to much problem?

Quote:
Surprizing that they did not make it also include the 80 meter band, but back then, I think 40 was the hot band of choice for most novices. You could wind the coils to resonate on 80 meters without any problems and it would work just fine on 80.


Could I do that and still hit 40 and 15 meters?

Right now I have no idea what the "hot bands" are, but I want more than the "line of sight" range that you get with 2 meter radios.


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PostPosted: Sat Feb 07, 2009 10:51 pm 
You can very easily use a relay to key the transmitter. I have used a mercury wetted relay to key my boatanchors for many years, but I will have to admit that I get sort of carried away with speed when I am working a crack CW operator and at speeds over 30wpm some relays won't follow that closely, so the CW gets clipped. However, no need to worry about that anymore, as I have lost the manual dexterity in my hands to do much over 20 or 25 wpm nowadays, even with a keyer. I guess arthritis has some benefits. HI!

But using a glass envelope 6L6 would be a disaster waiting for a place to happen. The metal shell 6L6 is shielded very good when pin 1 is grounded thru a very short connection to the chassis.

I have never been a fan of link coupling to an antenna. Even my very first transmitter I built called or link coupling, but I never even contemplated that. I used a pi network instead. You got way better harmonic suppression with a pi network and it would load up to a random antenna a lot easier than any link coupled output circuit would.

One of the major advantages of the Colpitts oscillator is that one side of the crystal is grounded. This greatly simplified crystal switching, as only one lead needed to go thru a switch. Also it was much easier to couple the mighty VFO to it when the big day arrived when the general class license arrived in your mailbox.

I realize I was a pathetic nut case back when I was 15 years old. Here I could not even build my first CW transmitter without completely re-designing the circuitry. Like I was already an old pro at building transmitters it seemed. I was hauled in before the Radio Inspector for the FCC after I had my novice license for only three months, and back then it was good for a whole year. It was not until I sat down with a bunch of other kids that the RI welcomed us and informed us that we were starting the day taking the General Class license test! Hey, I had hardly cracked a book since getting my Novice license three months earlier, as I was having so much fun operating. I sailed thru the 13 wpm code test with a worn out J-38 key and a foghorn for an audio oscillator and then proceeded to ace the General class license written exam. My Elmer, who shanghied me to take the trip to Spokane, Washington with him under the pretense of going to visit some radio stores prodded me to take the Advanced, but I was too worn out for the day. So that came a five years later, in 1970. Then four years later in 1974, I passed the Extra in front of the RI and the day previous, I passed the First Class Radio Telephone tests. When I showed up to take my Extra, the RI looked at me and asked if I was a glutton for punishment and I told him "I guess". But I got it all done with 35 years ago this May. Back then the only license tests given by volunteer examiners were the novice and conditional class licenses. All others were in front of the RI and you were literally quaking in your boots when going up before him.

The good old days! Heck, it just dawned on me that this coming Thursday, February 12th, it marks me as being a licensed ham for 44 years!
Curt


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PostPosted: Sat Feb 07, 2009 11:10 pm 
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Joined: Sat Aug 18, 2007 8:52 pm
Posts: 2767
Location: Australia
Quote:
Thursday, February 12th, it marks me as being a licensed ham for 44 years!


Good on you Curt. Looks like you're just as 'mad keen' as you were then. Must have given you a life-time of fun.


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PostPosted: Sat Feb 07, 2009 11:25 pm 
Well, sadly, I suffered major burnout with ham radio seven years ago. Over the years, about the only thing on HF that I did not try was slow scan television. Years ago I was into RTTY with a model 19 page printer and such. I have worked mainly CW over the years, but have not neglected AM and even messed with slopbucket a time or two. I remember operating narrow band FM n ten meters with a Multi-Elmac AF-67 years ago. I built high power amplifiers (usually a pair of 813's) and operated QRP using a solid state rig I built back in the 1970's. I was always involved in Emergency Communications and worked my share of DX, to the tune of nearly 300 countries, but I never did count them, as I was not a card collector. Spent many years studying propagation at HF and antennas. I pretty much done it all and I always dove into everything head first when I ventured into something different. The last couple years of my activity were around mobile HF CW operations with a homebrew antenna off the back end of my van and assembling a complete and 100% pure stock SCR-274N Command Set setup that I had fun making contacts with.

It usually blew others away when I told them they were hearing the same signal that would have been transmitted from a B-17 or B-24 or even a P-51 during the war. Batteries, dynamotors, and the whole ball of wax.

As a result, I very suddenly simply crashed. I had the Command Set special all set up on the kitchen table and I got done working a couple guys and turned it off and walked away from it and it sat there for a whole week, while I ate on a TV tray. I just did not have the enthusiasm to dismantle it all any more. I have not emitted an electron since and that was in October of 2002.

I renewed my license last year, so I am good there and hopefully I will get back on the air in a couple years. But right now, I still have not fully recovered from the burnout I suffered. Still got the Kenwood TS-830, but it has not been turned on since then and the capacitors in it are probably all dried out by now.
Curt


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PostPosted: Sat Feb 07, 2009 11:33 pm 
Curt Reed wrote:
But using a glass envelope 6L6 would be a disaster waiting for a place to happen. The metal shell 6L6 is shielded very good when pin 1 is grounded thru a very short connection to the chassis.


If the issue is shielding, could I just put an aluminum shield around the tube? Or are there other issues?

And: What would you think about a 6BG6 for a final? I looked and it's the only power beam amp I have right now with the plate on top. The specs I looked at look like it could more than handle a curcuit like these.

Oh... And thanks for taking the time to answer my questions. One way or another I'm going to build a rig like this, I might as well try to make it a good one.


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PostPosted: Sun Feb 08, 2009 12:43 am 
There is absolutely nothing wrong with the 6BG6 tube! Some hams referred to it as an octal based 807, whereas I referred to it as a double ended 6L6. Interelectrode capacitances are a bit higher than an 807, but for 80 and 40 meters, who cares? We are not talking VHF here. A good tube shield for them can be constructed out of a small (8 ounce) tomato sauce can. What I have seen a lot of hams do is when they are cutting the socket hole with a Greenlee punch in the chassis, was to simply include the can bottom also and when you mount the socket, it will also mount the can which is the shield. The main thing is to get teh part below the plate structure of the tube shielded. The plate and top cap can be exposed for ventilation. The 6BG6 seems to have been a forgotten about sweep tube in the archives of ham radio.

If others think we are getting carried away here, I am sorry. If you desire, you can e-mail me directly and I will answer all your questions there, but I prefer to keep it on the forums as others can learn and it may strike up some other fond memories from some old timers also who may wish to jump in. The more the merrier!

I don't normally carry on like this here on Dave's forums, but if you have been a member of the ARF for very long, you will soon see that it is just a normal way I go into things over there. Maybe that is what broke the server?
Curt


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PostPosted: Sun Feb 08, 2009 12:55 am 
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Location: near St. Louis MO.
Hi Mike & Curt .

I was wondering what RFI looks like on a digital TV .


Mark


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PostPosted: Sun Feb 08, 2009 1:23 am 
I would have absolutely no idea. I have the TV set disconnected and have not had it on for nearly seven years now. People were talking about turning off their TV sets for a year back then to help their kids grow up properly, I remember. So when my mother who used to live here got behind in her bill paying due to dimentia the cable company cut off the cable. After she moved to a rest home, I tried to see if I could go for a year without the modulated milk bottle. That year turned into seven years so far and I don't miss it one single bit.
Curt


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