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 Post subject: Jones PP transmitter with RK34. Now with 6A6!
PostPosted: Jan Wed 06, 2010 10:08 pm 
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Planning to build a couple Jones push pull transmitters. The first will be by the book using a #53 tube. This will be for testing purposes and the fact I have a power supply with the right voltages.

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The second will use an RK34 dual power triode that I have.


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I'm wondering if I can increase the plate voltage with out damaging the tube. I hope to get more then 10 watts out of this tube, more like 30-40 watts. Any one have experience with this tube? Open to all hints and help.

John
KB7NRN


Last edited by War Bird Radio on Mar Fri 12, 2010 2:07 am, edited 1 time in total.

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 Post subject:
PostPosted: Jan Wed 06, 2010 10:23 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
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Location: Sandpoint, IDAHO 83864
The tube is only rated at a maximum of 24 watts input. Trying to get more power out of it will result in greatly shortened tube life, and those tubes are not very common nowadays. Also, since it is a crystal oscillator set, you run the risk of breaking the crystal with too great of crystal current when you go exceeding the tube ratings.
Curt

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 Post subject:
PostPosted: Jan Wed 06, 2010 10:41 pm 
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Curt,
This was a VHF tube, full rating is good to 220 mhz. At HF freqs wouldn't it be able to put out more RF?

Also, the orginal #53 had a plate disapation of 1 watt but they got 10 watts RF out of it. Why is that tube not over stressed?


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 Post subject:
PostPosted: Jan Wed 06, 2010 11:04 pm 
Silent Key

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Hams used to do a lot of bad things with tubes. I can well remember lots of hams running an 807 or 1625 at a hundred watts input.......for a while! If you have a good stock of these tubes, then go for it. But if the tube goes bad in a short while, don't come crying in your beer.

I would be more concerned with crystal current, however. When that circuit was designed, the crystals were larger and could take a lot more abuse than the post-war crystals and the puny things they call crystals today.
Curt

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 Post subject:
PostPosted: Jan Wed 06, 2010 11:23 pm 
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Ok Curt,
I hear your warnings. No I don't want to ruin this RK34 in short order so I'll keep it running cool...

But then I found this Jones TX. Push pull 6L6G's at 50 watts out. 'Ol Frank liked to run things hot didn't he.

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 Post subject:
PostPosted: Jan Wed 06, 2010 11:29 pm 
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Id replace the 6L6's with a cheap 829B/3E29/5894 or an 815 if you can live with less power. Easy socket availability for the former and the 815 is octal.

Carl


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 Post subject:
PostPosted: Jan Thu 07, 2010 12:29 am 
Silent Key

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Just remember that W6AJF had every tube he ever needed at his immediate disposal and I doubt he ever paid a nickel for any of them. It was his job to write articles like this for Radio Magazine and he got kickbacks from the manufacturers in the way of free tubes and parts for the articles if they were printed. Good advertizing for them, especially when he ran tubes way over the limit, as more tubes would then be sold.

All his designs were good designs, but I don't think he ever knew how to operate a tube conservatively.

But he was not the only one! I recall a single tube crystal controlled transmitter that was good for 150 watts output and it used an 813! It was either RCA or GE, but it was on the back cover of QST Magazine back in the late 1940's. I wonder how that boosted sales at the crystal manufacturers?

Yes, I like Carl's idea of using an 815 dual tetrode. An 829B would also work, but finding sockets for them nowadays is problematic, but the 815 uses an octal socket. I recall we had an ARF member asking in the Classifieds forum for an 829B socket and it took him several months to find one.
Curt

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 Post subject:
PostPosted: Jan Thu 07, 2010 1:01 am 
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When I worked in Land Mobile Radio I had more 829B's and sockets then I care to remember. But that was almost 10 year ago now. When other hams found that I had them and offered good money or trades... well, they all went.

I have ceramic seven pin sockets for the 53 & RK34 so I'll try those.


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 Post subject:
PostPosted: Jan Thu 21, 2010 7:36 pm 
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Decided to go with the 6N7 instead of the #53 since the former is just a rebased #53 with 6.3v heater. Also found that my tube manual has the wrong data for the #53 family of dual triodes. My GE manual says they all have 1 watt plate dissipation but but the RCA manuls say they have 5 watts, per plate I think. That makes a big difference.

Anyway I threw this together last night from parts on hand, didn't go out and buy anything just dug in all my junk boxes. Even the base board is reused from the first regen I built. Hope to wire it today. We'll see.
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The coil will be tapped on both ends with the clips shown for easy band change. The double terminal in front is for the key.

I started the RK34 PP TX but am waiting for parts.
After looking at the specs closer I wonder how it will perform. It says it needs 1.8 w drive! If it doens't work then the parts will just go for other projects.
Image
Image


Last edited by War Bird Radio on Jan Fri 22, 2010 2:37 am, edited 1 time in total.

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 Post subject:
PostPosted: Jan Thu 21, 2010 9:25 pm 
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Already starting to look like a shelf queen and you just started. What do you call a transmitter that looks like a shelf queen anyway?

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 Post subject:
PostPosted: Jan Thu 21, 2010 11:51 pm 
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bill hamre wrote:
What do you call a transmitter that looks like a shelf queen anyway?


A relay rack transmitter!


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 Post subject:
PostPosted: Jan Fri 22, 2010 1:01 am 
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Like this:
Image
Courtsey of W9QZ.


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 Post subject:
PostPosted: Jan Fri 22, 2010 1:05 am 
Silent Key

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War Bird- that thing is absolutely BEAUTIFUL! If I were to build something like that, the only difference would be I would use UX tube sockets,as they would be more period correct.
Curt

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(Connoisseur of the cold 807) CW forever!


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 Post subject:
PostPosted: Jan Fri 22, 2010 7:24 pm 
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NOW THATS WHAT I CALL HOMEBREW !!!!!!
that is one dynimite job there warbird, have you put it on the air and played with it yet ??

buck


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 Post subject:
PostPosted: Jan Fri 22, 2010 7:33 pm 
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Drool...

That's a work of art...

Tom


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 Post subject:
PostPosted: Jan Fri 22, 2010 10:12 pm 
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The last transmitter was not built by me. Rick Weber, W9QZ bulit it a few years ago to use in the AWA 1929 CW contest. That's a ham radio morse code contest put on every year for tranmitter designs 1929 and older.

Curt is right, the old UX bayonet type tube sockets would look more period. It is a beautiful transmitter but I've never seen any photos from the era that was as elaborate. Most were more utility looking.

The other thing is, this is a free running power oscillator type of transmitter. It is not crystal controlled so it has a tendency to shift freq as the antenna blows around in the wind. They also had more of a buzz then a pure audio tone when reciving their signal. Not sure what tube he's using but it probably didn't put out more then a couple watts.

It's a lot of work to go through to build a transmitter like that given it's limitation but you really get a taste of what radio ops were up against back then.

John


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 Post subject:
PostPosted: Jan Sat 23, 2010 1:13 am 
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I remember reading a description of a 201A TX using I forget, 300? 500? volts on the plate. A short dash turned it red, a long one melted it.

Dave


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 Post subject:
PostPosted: Jan Sat 23, 2010 1:24 am 
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Dave,
Yeah, the '01A wasn't designed for much power output.

Below is Rick Weber's first Hartley transmitter that he says is using an '01A at 0.5 watts out.
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 Post subject:
PostPosted: Feb Tue 16, 2010 7:31 pm 
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Update:

The 6N7 PP TX works pretty good. I've experimented with different link windings for 160 - 30 mtrs. 160 mtrs seems to give the best performance. Because of the compact size there seems to be close coupling between the input and output causing too much feedback on the higher freqs. This causes the xtal to heat and change freq slighlty which results in a "yoop" sound when received. On 80 mtrs it's not noticable except with the smaller HC6 and 49 xtals, especially on the HC49's. The unaltered FT-243 don't have any problems and are rock solid on freq. But alas I only have out of band FT-243 xtals for 80 mtrs. That's out of the CW band that is. I have one for the old novice band at 3710 kc and one for AM at 3870 kc. They work FB!

In the bags of xtals I aquired recently I found three at 1795 kc. I have ground two of them up to 1814 & 1820 kc. Was trying to hit 1810 kc which is the CW QRP calling freq. Still have the last one to hit 1810 kc with.

The transmitter does very well at 160 mtrs. With the two xtals I ground I have at least nine xtals between 1800 - & 2000 kc and I have tried them all. FT-243's , HC6's, HC49's and large vintage xtals all work with out heating the xtal and no "yoop".

The TX is putting out about 7-8 watts RF with 350 vdc on the plate and a clean tone. Added a .01 uf cap across the key terminals to eliminate key clicks and padded the variable cap in the tank circuit with an additional 100 pf so it wasn't near closed at the bottom of the band. Remove the shorting wires from the tank coil.

Called CQ a couple nights but I guess no one want's to answer a slow speed, low power CW op. I gotta set up a sked with someone to get some on air reports.

Photos below of the 6N7 PP TX while testing on 80 mtr.

The RK-34 didn't work well at all. Seems the oscillator wanted to free run and the xtal could not hold the freq. It would be easy to sub a #53 in place of the RK34. The only change would be to move the plate connections to the tube base. It's shelved now waiting for more interest and a #53, since I'm moving on to the MOPA rigs.

John

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 Post subject:
PostPosted: Feb Tue 16, 2010 8:00 pm 
Silent Key

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Location: Sandpoint, IDAHO 83864
Just got to ask a question. What part of the circuit are those two RF chokes in that are alongside each other. That MAY be a major problem.
Curt

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