The AM Forum

After spending some time chasing a AM transmitter around to buy I got to thinking.
Homebrew one?
I built a few receivers over the years, couple of amplifiers, and a 6 meter tranceiver so why not a AM transmitter?

Couple of years ago I got to wanting an HF amplifier. So I found a case and starting collecting parts.  I later found a decent amplifier and never got back on the homebrew one.

This is the chassis I was working with.Have no idea who made it but I seen it in other contruction.
(http://gokarters.com/smf/index.php?action=dlattach;topic=2143.0;attach=275;image)


I had already laid out a lot of parts in the case for 4 811 tubes
(http://gokarters.com/smf/index.php?action=dlattach;topic=2143.0;attach=274;image)

Not really looking to build a high wattage transmitter. Maybe something with a single tube, 6146 maybe. Been thinking this over for a bit of a week. looked at a few schematics but not nailed anything down yet. Really think it will be a fun project for the winter.

Roll up a 813 and mod it with the 811s. You'll get some RADIO leg for sure.


klc

Thanks for that suggestion. have any links or documentation? I will seach the web and some books later tonight and see what i can find. not sure if my cabinit is going to be big enough

A really good design for a self contained 813 rig is the Vernon Chambers transmitter.   The part count is pretty high so it will likely take awhile to get the parts but its definitely worth the effort.  

Here is a link to the 1954 article which describes the transmitter.  Most of the folks that use a pair of 811's to modulate it.  Bob - W2ICQ and Dave - KA2J use theirs quite a bit and really have high praise for it.  Another member here on AMfone is currently building one.  

Regardless on what you end up building, nothing is better than doing a HB rig.  

Joe, W3GMS  

Hello Joe,

i don't think there is enough place in this box to build " the vernon chambers " transmitter!

John

Thanks Joe for that info.
I will look this over first chance I get. 12 hours a day for next 3 here at work.


I can get another cabinet :)

Lots of ways to go. Is your decent amplifier up to the task of being a decent AMplifier? if so a good quality AM exciter would be something that would fit in that cabinet.

At the moment I do not have an amplifier. I sold my Johnson Thunderbolt 7 months ago. Was not thinking of AM during that time and the amplifier was not being used.

Can always find or build another.



(http://gokarters.com/smf/index.php?action=dlattach;topic=2287.0;attach=1171;image)

The entire Chambers transmitter information, including the supplemental/update articles, are also available on the ARRL AM page http://www.arrl.org/am-phone-operating-and-activities . I don't think the Handbook article has all the supplemental info.

Three Control Six-Band 813 Transmitter

o    QST, Jan 1954, pp. 11-16, 112, 114, 116
o    QST, Jun 1954, pp. 37-39, 118 
o    QST October 1956, pp. 33-38
o    ARRL Handbook 1957, pp.192-197 

Maybe just barely fit a whole TX in there. Power supply too? would be challenging an a tight job for cooling too!

Was thinking external power supply.
I called around today looking for other chassis. Thinking of building one that is about the same outer dimensions of my chassis, but maybe 2-3 feet tall. Sit the smaller unit on top.

You may wish to look at the Maytag for design ideas. Its got an 813 modulated by (2) 811s.

Here's a pic to give you an idea of the size.

The AN/ART-13 was built to mill specks as an airborne transmitter. The specs are conservative; juice the plate voltages and the 813 will sing loudly. The schematics are online; you could home brew one up with out all the auto tune stuff. Then you could cruise the bands, and squalsh the qwermers like a bug. You would have a maul.  It would be beautiful.


klc

Appreciate all the suggestions.
I see have quite a few decisions to make.
The first one is which to build. Time to clean shop and take inventory to see what I have and what I need to hunt down. This will take a while. I never been a copycat and when I build stuff I like to add my own twist to things. But may not be the case here, may stick with something that is proven to work.
Looks like a nice long winter project.

Hello kc4umo
May be this diagram could be good for you :)

You bet it will :)
I will print it out on 11x17 at work tomorrow,

Thanks

Boy!  That schematic is a blast from the past!  That's the schematic for the ELDICO TR-1.  I had one of those in the '50s.  It followed me around to two college locations and then to my home in Manchester NH.  I finally scrapped the RF deck and rebuilt the final.  The power supply remained intact and improved with a soft start for the HV turn on.

The RF deck was completely reworked using 2 x 813's in PP.  It served me well both in Am and RTTY service in it's second iteration - a very cool 500 watts input

The modulator used the ART-13 driver for the 811 tubes and the modulation transformer from the same transmitter.  I have about 3 of those transformers - one of which was removed from the original TR-1 deck.  I still have the original 811s (not 811a) from that transmitter.

Memories

I'd dispense with the RF driver section and drive it with something more modern.  If you duplicate the original TR-1 modulation setup as shown in that schematic, it will sound a bit restricted

Al

PS:  I'm thinking that schematic was as originally photographed from my paper copy.  The folds and discoloration fall precisely in the same location.  Here's the original thread from a few years ago:

http://amfone.net/Amforum/index.php?topic=24779.0

Good to see that the design of the old girl is still making it's rounds

Al

If your looking for low parts count AM I am currently using this one. One 6l6. Also have one with a single 45 tube and some here have worked me with that one. Have also built a few screen mod rigs with 2 tubes. Then you could finish your 811A amp (mine has only a pair) There is no feeling like "talking " on a simple rig you designed and built yourself glowing beside you the heat rising from the glowing tubes, the meters wiggling and your heart pounding as you call is finally returned. The grin of unbelief as an idea becomes a working radio.
You know what you need. An osc first, a way of providing modulation,(you choose, its your dime)  some power boosting and a good antenna.
don

Nice Al. It is always good to see things of that sort come up.  I once desinged a new antenna for 70cm to use on oscar communications. Saw a post on a yahoo group where a chap from England built the antenna after my design.  Sure puts a smile on ones face.


Don,
Nice speech!
Makes me want to get motivated.  I always like it when folks post schematics and someone follows up with pictures. Helps a lot in the design stage as to where everything needs to be.

Anyway decided not to scrap my amplifier project and build in that case.
Think I am going to roll my own chassis. I made a few spot welders out of microwave tranformers so that would be a breeze.
Plus who knows, may have to homebrew a MATCHING RECEIVER!

PS,
I just wanted to say this has to be one of the best forums I ever joined. You just do not find so my knowledge anywhere that is ready to help.
You guys should be very proud of yourselves.

 :o What to do, what to do?  I've heard about the legendary 813 single-tube transmitter.  Why?  Then there is the over-complex rig from the early 50s that was constantly being modified.  Then there is how much experience do you have?  I'm still learning thanks to this bunch.  My advice is take it really slow.  I've bought and sold so much stuff because I kept changing my mind that I finally got the 250 watt modulation iron I've been looking for.  Fifty years, easy!

If you don't have a lot of building experience, don't expect to fill that cabinet by tomorrow.  What a great hobby! ;D

The PDF below is a 11X17 version of your TR-1 schematic.With some diddling, the darken fold fines from the acidic paper probably could be further cleaned up.

For those of you who have large schematics that are getting older, the FedEx Store/Kinkos has a scanner that will do 42 inches wide x unlimited length.

I had them scan the 3 ft x 5 ft master schematic for my Gates BC-1G. The blueprint had been folded since 1955, was very blue overall and had many splits at the folds. They successfully scanned it, without damaging the original and showed me the original scan which had all the visual  faults of the original and then ran it through their clean-up program which got it back to near original 1955 look. The whole process with scanning the large print, scanning the whole manual, including three large fold out schematics, and printing three copies of everything cost just about $100.00. They even included the fancy folds on the fold out schematics in the spiral bound copies and a thumb drive with the whole thing on it. I was seriously impressed!

The problem with large engineering-type drawings done back in the "good old days" with very acidic processes and using today's automatic clean-up programs (I've used the FedEX/Kinko machines in the past) is that they can't always distinguish dark fold line areas from actual circuit lines especially when they fall on top of each other. Where the dark fold lines fall over circuit information, you generally have to go to a manual process and clean it up by hand. One tip to remember if you have any of these old large engineering-type drawings with multiple folds. At each fold where one side of the actual drawing side lays on the another drawing side (I call it the "print-to-print" side), put a clean sheet of white paper between them at the fold. This will reduce both printed sides from interacting with each other making even wider darker areas at the fold points.

I've diddled with hundreds of these engineering-type drawings (2X, 4X, 6X, 8X) over the years that have dark fold lines and where paper that has turned various shades of brown. In many cases, when machine cleanup processes get you only so far, water-based "white out", will take you the rest of the way. Sometimes, depending on the drawing and the nature of its faults, reverse imaging processes (white on black rather then black on white) actually work better to produce a good useful drawing.

Talked with a local that would cut me all the panels for 2 chassis. All I have to do is put them together. Problem is he is very busy and said it would be 2 months. Just about when it gets good and cold.  In the mean time I will be gathering parts and playing with a few circuits for the transmitter.

Also I decided to drag the Apache's back out and work on trying to get up and running.  The one I am working on shows a little sign of life. Going to recap it, re clean all switches and take some voltage checks.

There is no output at all. But did manage to see the meter come up in HV mode and get a reading with the meter in drive mode. Shows nothing in grid or final setting. I even manage to get a little shock from it, twice. While holding the TX switch with one hand and touching another control with the other it gave me a good tingle. Tomorrow I will rep[lace the 2 wire power cord wit ha 3 wire and see if I can ground the chassis.

So many projects :)

 :) Buddy!  Go to onlinemetalsupply.com attn: Steve Pierce.  He has done a lot of work for me.  He will cut to specs for a small charge.  Highly recommend and super-fast service.  A week at most.  Everything from chassis grade to front panels in your choice of aluminum hardness.  He has included a tutorial on how to pick aluminum.  Like a good nose, pick it!  ;D

This is how the 36 x 70 inch main schematic came out after cleanup...

http://bh.hallikainen.org//uploads/GregCotton/Blueprint36X70.pdf

It was ugly before they cleaned it up, I'm not sure how much of that was manual work and how much was the automation.

I dumped the whole manual and schematics into the archive over there if anyone needs it.

No manual cleanup. It looks they just reduced background contrast and lightened intensity almost probably to its limit. That's why some of the circuit lines are almost completely washed out. One way around that would have been to make a finished copy before the lines start to wash out and then run it though the machine again at 75% (rather then 100%) and with reduced background contrast. Since the copy is now 25% smaller, the circuit lines actually would look darker and more background junk would disappear.