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Author Topic: Classic 6L6 Homebrew Transmitter Help  (Read 40120 times)
KG7RS
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« Reply #15 on: December 18, 2010, 04:56:05 PM »

Well Folks, if anybody is still monitoring this thread -
After thorough experimentation with a single-tube power oscillator I've come to the conclusion that for many reasons - they suck wind! Certainly not a lot of fun on the air. I did manage to make contacts but chirp is bad. After careful tuning, chirp can be improved but due to instability, it will get bad again in the middle of a QSO. I decided I've had my "fun" with it and it was time to abandon the single-tube design altogether. Those poor novices "back in the day"!

It was a simple matter to install a genuine James Millen FT-243 crystal socket and use the octal socket previously occupied by a crystal for a separate oscillator tube. Then, gut the underchassis circuitry and start over. I built a 6J5/6L6 design out of the 1947 Radio Handbook (Editors & Engineers). The complexity is hardly more than the original power oscillator transmitter but after it was completed - what a difference! No chirp! The oscillator runs all the time that HV is applied. Stable as a rock. I also changed the companion power supply from choke-input to capacitor-input which resulted in B+ now at 425V key-down. The transmitter loads to just under 70mA and gives about 15-16 watts output. Working stations on 40 CW is like falling off a log now.

B+ is a bit higher than I wanted but should be OK as long as I keep the key-down to a minimum during tuning (fast and easy with link coupling anyway).

I'll post new pics later.

73, John, KG7RS
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N2EY
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« Reply #16 on: December 19, 2010, 06:06:05 AM »

After thorough experimentation with a single-tube power oscillator I've come to the conclusion that for many reasons - they suck wind! Certainly not a lot of fun on the air.

DEVIL'S ADVOCATE MODE = ON

Me thinks you doth protest too much.

There are single-tube oscillator transmitters that don't have all the problems you encountered. I know; I built one as a Novice.

The real problems with such rigs are:

1) there are a lot of designs out there that aren't very good. For example, using a beam-power tube that has the BF plates connected to the cathode internally isn't the best choice for an oscillator where the cathode isn't grounded for RF. But lots of designs use such tubes anyway, with odd results.

2) there are a lot of designs which depend on a particular part or setup, such as pre-WW2 X-cut xtals that can handle lots of RF, or 80 meter operation, or a power supply with good regulation, etc. Change a critical factor and the results aren't pretty.

I'm glad the revised design works better. But please don't condemn a whole class of rigs because of one bad experience.


73 de Jim, N2EY

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KG7RS
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« Reply #17 on: December 19, 2010, 09:02:57 AM »

Jim N2EY - Guilty as charged! You're right, I shouldn't condemn the entire lot until I've studied and experimented more. This was all about nostalgia for me. I used to dream of building a simple single-tube rig when I was a young kid with only a fleeting knowledge of ham radio but with a strong interest to learn all about it. Oddly enough, when I pour over those old books today, I get the same feelings now as then. This single-tube design was somewhat of a disappointment for me. I most likely could have made it usable but the point is - with only one additional tube and a scant few additional components - why bother?

I had a ball with the new version last night. Worked three solid QSO's including one rag chew with a fellow in NM that lasted just shy of 1-1/2 hours. Although a bit CW-rusty, I bet I could actually carry on a QSO at the 20WPM I once passed!

At the risk of leading this thead astray - homebrew activities like this are what ham radio is all about as far as I'm concerned. It seems the "magic of radio" is completely lost to many of us. The capability of modern equipment is phenomenal. For me personally, it took something as simple as this little transmitter to rekindle the magic of radio that has slipped away in recent years. Perhaps not everyone is as nostalgic for the "old days" as I. A kit such as an Elecraft K1 may be just the ticket to rekindle the magic. Like any endeavor, you get out of it what you put into it.
73, John, KG7RS
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KG7RS
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« Reply #18 on: December 19, 2010, 10:18:04 AM »

Images of the new 2-tube transmitter:

http://www.getnet.net/~corsair510/novice1.jpg
http://www.getnet.net/~corsair510/novice2.jpg
http://www.getnet.net/~corsair510/main.jpg

Yes, I know that NC-270 is a bit "modern" for a prewar-style transmitter. Anyone want to trade for a National NC-100X?....HQ-120X?...hee! The little gray box next to the receiver is a homebrew T/R switch that includes a series variable capacitor to load the transmitter's link coupled tank coil to my modern antenna.

Main station features a very nice Johnson Viking II and a "New Old-Stock" HQ-100A.

My third station fits in a camera bag - Yaesu 817ND, HF Packer Amp, Lithium nanophosphate battery pack. A second small tripod bag holds a Tarheel 75A screwdriver antenna setup for portable use complete with homebrew wireless up/down motor controller and self-contained lithium battery pack. After all, I'm not a complete "Old Buzzard" yet!

Fun thread - 73 all, John, KG7RS
« Last Edit: December 19, 2010, 10:20:34 AM by John Tucker » Logged
VE3LYX
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« Reply #19 on: November 27, 2011, 07:30:51 PM »

I dont have a 6l6 but I do have a 50C6 tx. I used to run a 50L6 and it makes very good power. More than I need. It is on 80. I have run all the types of crystals in it including the 3579.5s So far I haven't cooked any. Ist contact was 567 miles as the crow flies. The circuit is called the Bare Essentials rig but i made it more conventional and used he older octal tube. (1934) If you wannna hear it set up a sked. It has a conventional tank circuit parrlel tuned It has lots of suds. Key well too. I run it on a transformerless doubler . Key down is about 280V It tunes nicely. I use a permanently installed Light bulb rf loop to tune the tank.I run it into a base loaded inverted L
Infact you can see and hear it on you tube. I will give you the link in a minute. A6l6 should put out more butthe tubes are very similar both even use 7AC pinout diagram.
Don Ve3LYX
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VE3LYX
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« Reply #20 on: November 27, 2011, 07:34:21 PM »

http://www.youtube.com/watch?v=BWvKgFl1lAw
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VE3LYX
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« Reply #21 on: November 27, 2011, 07:36:57 PM »

http://www.youtube.com/watch?v=BWvKgFl1lAw
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YS1RS
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« Reply #22 on: July 23, 2012, 11:42:20 PM »


I second that emotion... The black crinkle finish is not only boatankerly accurate, but it looks good.

Now, as to flavors of the 6L6: If you want to be true to the original RCA design you're looking at a metal tube. Good luck in finding one. Probably worse than your experience in trying to score an ST (Coke bottle) glass version of the 6L6. I've been rebuilding some Seeburg juke box amps and can tell you the metal and ST versions are about 3/4" taller than the modern style and might look odd peeking out above the front panel. On my jukebox amps the top cover will not clear the ST or metal tubes. I've tried both.

BTW: In terms of vacuuminus pulchritude the 837 is hard to beat... No kidding, it's as visually impressive as an 807 but with a style of its own.

http://www.tubecollector.org/main/837.jpg

Output is 20+ watts in class C telegraphy, much taller than a 6L6, needs a 7 pin ceramic socket, plate cap, 12.6 volts on the heater. I have a small stash of these in the garage and sommmmmmmmmmmm daaaaaaaaaaaaaaaaay...........

I know. This is a very old thread... but maybe someone will still see it....
Here I go:
Apart from an Ameco AC-1 Replica, I am also building a WWII radio transmitter. The biggest help came from a good friend in B.C. Canada, but also Ham radio guys from our radio club in my country started to gather a few parts here and a few there trying to help me getting all the required parts needed for my projects.
I was given a small box of old tube era parts by them.
All the parts inside the box were from a B-17 radio transmitter from 1944.
Now, in this box I found a beautiful 837 tube.
Do you guys have a circuit diagram of a one tube or at much two tube CW transmitter for 80-40 or 20 meters I could build using this 837 tube? Have not found much info on the internet regarding applications with this tube, but I read this could be used to build a CW transmitter in a 10W-20W range, which is not bad for me, being DX.
Sure this big nice tube glows beautifully with a soft blue touch in the dark...

72 and 73 de Rob.
YS1RS
« Last Edit: July 23, 2012, 11:47:44 PM by YS1RS » Logged

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AC5UP
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« Reply #23 on: July 24, 2012, 07:21:09 AM »

The 807 and 837 tubes were very similar with the 807 being the higher voltage / higher power version while the 837 used a 12.6 volt filament. The 6L6 is another variant in the 807 series of Beam Power Pentodes promoted by RCA in the 1930's. Meaning............ Although they're not exactly the same, an 837 should work as well as an 807 or 6L6 in a simple transmitter circuit as long as you keep the plate voltage below 500 VDC (max) and avoid tweaking for maximum smoke. (the 807 is rated to 750 VDC, the 6L6 to 375 VDC)

If you're seriously considering rolling your own vintage ether beater your next stop will be here:  http://tubebooks.org/technical_books_online.htm#Radio%20%28transmitters,%20receivers,%20design,%20repair...%29

Download the two W6SAI / Bill Orr radio books (they're excellent) as well as the two ARRL Handbooks (1936 and 1941). Either will give you a good idea of how this was done back in the day and the 1941 ARRL Handbook in particular has a couple of simple 807-based CW transmitters that should easily adapt to an 837. If you have some engineering background the 1961 Radio Transmitters book is another good choice. It assumes you've been around the block a time or two and includes a wealth of reference & design information.

If you ever need a quick look at tube characteristics, go here:   http://www.nj7p.org/Common/Tube/SQL/Tube_query.php?index=1
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G3RZP
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« Reply #24 on: July 24, 2012, 07:56:08 AM »

http://frank.pocnet.net/index.html is often better than NJ7P - it has the characteristic curves
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K8AXW
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« Reply #25 on: July 24, 2012, 09:06:32 AM »

John.... ur links won't fly.  Are the photos still there? 
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YS1RS
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« Reply #26 on: July 24, 2012, 11:16:29 AM »

Thank you so much Nelson. So much info on those links.
Have gotten all that is required in those books.
Thanks for sharing them.
Will let you know once I have my vintage station on the air.

On the other side... the link to the photos by KG7RS is broken as is an old post from 2 years ago. I wanted to admire the photos too.  Sad
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AC5UP
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« Reply #27 on: July 24, 2012, 01:58:01 PM »

I hope some of that proves useful as one of the better ways to understand how things used to be is to read the literature of the day... Never fails to amaze me how clever some of the solutions were given the limitations of the hardware, but if you truly understand the theory you'll figure away to apply it. And so they did. People built effective antennas before the MFJ analyzer was invented and used them to work the world on 20 Watts or less. When you see the articles like a "400 Watt Plate Modulated Phone Transmitter" remember that was an ungodly expensive device in the 30's and many Hams couldn't afford anything approaching 100 Watts until after WW II and military surplus gear became abundant.

Thanks for taking the time to let me know you took a look at the links. Now all you need is a rainy afternoon with nothing else to do.................   Wink
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YS1RS
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« Reply #28 on: July 24, 2012, 05:01:12 PM »

I hope some of that proves useful as one of the better ways to understand how things used to be is to read the literature of the day... Never fails to amaze me how clever some of the solutions were given the limitations of the hardware, but if you truly understand the theory you'll figure away to apply it.

And so they did.

Thanks for taking the time to let me know you took a look at the links. Now all you need is a rainy afternoon with nothing else to do.................   Wink

I downloaded many of them already.  A good companion to my only tube book I have. It's called "RCA Receiving Tube Manual" from 1965 (inherited from my grandfather - A radio broadcast pioneer in my country in the 40's). Never worked with tubes myself, as when I was on high school, started right away working with transistors. My only tube experience was with grandpa, I use to hold the flashlight for him when he was repairing those old tube radios, record players and reel tape recorders. Used to look, find and pick up that little screw or nut that fell from his working table, with my young eyes (I was 6 at the time).

It is difficult for me to find the required parts for tube projects. Everything has to be ordered from outside. You can find anything here in YS for computers, modern electronics like ICs and transistors, etc but nothing Radio related like varcaps, big resistors, tubes, chokes, transformers. This are simply non commercial, so not worth to offer this to the public.

Have almost everything to build my Ameco AC-1 replica except for one single 2.5 mH RF choke.
Regarding the WWII radio, I will use a power supply that will also be used for other projects. Have had problems looking for a 50K x 5 Watts resistor for the Power Supply.

Apart from that... all is going well.

Rob.
YS1RS
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YS1RS
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« Reply #29 on: December 22, 2012, 09:50:17 PM »

Guys good news!!!

Have finished my Ameco AC-1 repro I mentioned in my last post above.
You can see it here: http://www.youtube.com/watch?v=xs8B9m4_BuI&feature=share&list=PL389BC069C6038695

Thanks for all.

I am building another one tube transmitter with a 6AG7.

Un abrazo.
73 de Rob
YS1RS

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