The AM Forum

Is  there any problem running only one output tube (6146) in a Heathkit DX-100 transmitter ?  I have been running one tube, it seems to work fine.  My thinking is with one tube I can compare tubes, even "match" tubes. I have the RCA tube manuals for the 6146 max ratings,etc. The DX-100 seems to tune-up fine at two power levels, 40 watts and 70 watts on the Bird wattmeter into 50 ohm dummy load. I can change from 40 watts to 70 watts, just by changing the load control setting. since 70 watts is "kind-of" high, I can run it at 40 watts.  At 40 watts : grid current is (1.6) ma., plate current is (110)ma., plate volts is 780 V.
At 70 watts : grid current is (2) ma., plate current is (130) ma., plate voltage is 780 V.
Question : Is this bad for the transmitter ? It seems to work fine. Thanks for any comments.

Radio won't care.
Watch your modulation.
When needing lower power to drive a linear....
Pull one tube? Lower the plate voltage? Change the tube to a 2E26 and lower the voltage.
Keith
WA1HZK

I ran your numbers...
At 70w out your input is 101w - about 70% efficiency - not bad. The other 30w is being dissipated by the tube and tank circuit. A bit over spec for the tube in phone but do-able for CW.

At 40w out your input is 85w - about 47% efficiency - terrible. The other 45w is being dissipated in the tube and tank circuit. Not very good at all.

At these power levels, your modulator will be looking into a much higher impedance than it was designed for. Hard to say what that will do. You should have plenty of audio though.

Also, your grid current numbers look a bit on the low side.

If you want to test a few tubes, fine. But I wouldn't make a habit of running it with one tube.


Don

Thanks for the replies. I have only operated it on CW so far. I saw in old books they ran one tube on some transmitters to lower output for "Novice" class operation, I wondered if it would work on my DX-100.
How did you go about "running the numbers", that is great info. I,d like to learn how to do that. Thanks!

Sure it will work, though the tube plate impedance will be off from its original design and may not reach full 1/2 power and efficiency will decline..

I wonder how many Novices in the day (with human egos the way they are) actually pulled out tubes to keep the power within the 75W limit?   ;D  Maybe a lot of them, considering the intense fear of the FCC in those days.

Reminds me of a story...

Back in 1964 as a 12 year old Novice, I had a deposit on a used 75W CW Ranger at the local ham store in Hartford for $125. I would bring in a few bux every week. Then a used Valiant appeared on the shelf for $125. I begged Corky, the manager, to let me transfer the deposit over to the 275 watt rated CW rig. I had big plans to carry it onto the bus for the 5 mile ride home. Yeah, sure. He flatly refused and said I'd jack it up to full power. So I ended up with the Ranger... [sigh]    
T

T,


Well, would you have given it the jack??


klc

Hell yeah - Corky was right! I would have loved to run it up to 300 watts into my long wire, got RF burns and most likely blown that Valiant up.

Once I got on the air in Dec, 1964, I found it extremely competitive amongst us young baby-boomers.  Everyone wanted to call CQ and have the world come back.  No different than today. Everyone wanted to call in a pileup and be the winner.  Everyone wanted to be the big schlong. It was evident from an early age we were all exhibitionists striving for fame and attention...  ;D.

Corky was darned right. He knew how we thought. It takes one to know one.  He owned one of the early Collins S-lines with a TA-33. He was an A++ channelmaster and knew the score.  

T

Running the numbers.

Plate voltage times plate current equals input power.
780 x 0.110 = 85.8 watts input

Efficiency is output power divided by input power times 100.
40 ÷ 85.8 = 0.46
0.46 x 100 = 46% efficiency

In your second example:
780 x 0.130 =101.4 watts input
70 ÷ 101.4 = 0.69
0.69 x 100 = 69% efficiency

A class C final, like in your DX-100, should run about 70% efficient give or take. The loss, about 30%, is dissipated as heat, mostly by the tube. That's why they get hot! ;D If your efficiency is very low, like 40%, you'll probably exceed the ability of the tube to dissipate that heat. A short life for the tube can then be expected. Maybe very short.


Don

Thank you for your very clear and informative answer ! I learned some valuable info. that will help me.
One last question,
 "the loss,about 30% dissipated"  , is this what the tube manual refers to as "plate dissipation"??
  Is that how I determine "plate dissipation"??
  (6146 : 25 watts Plate Dissipation), RCA tube manual.
Thankyou for your help!!

I ran a Viking 2 like that for YEARS! Never a problem. When I sold it I just dropped the second 6146 back in and all was well!

The tube manufacturer specifies the tube plate dissipation on their datasheets for a given application. That number is what is recommended as the maximum the tube can dissipate to have reasonable tube life. The difference between your power input and your power output will be dissipated by the tube. So, if you have 100 watts input and 75 watts output, then 25 watts must be dissipated by the tube. It's dissipated as heat - wasted energy. You'll then need a tube that can deal with that without going into meltdown. A small amount of loss occurs in the output circuitry but that can be neglected for this exercise.

On tube datasheets you'll see "Maximum Ratings". There may be a maximum plate voltage and a maximum plate current. You can do one or the other but usually not both without exceeding some other rating. You want to look at "Typical Operation". If you stay close to those numbers, you'll be good to go.


Don

Thank you for taking the time to explain this so well. now, I can better understand the information in the tubebook. Thank you you've been a real help.

Singing for their supper:

 ICAS classification: The use of tubes in Amateur transmitters, and the use of tubes in equipment where transmissions are of intermittent nature.
 "Intermittent operation implies that no operating or 'on' period exceeds 5 minutes, and every 'on' period is followed by an 'off' or standby period of at least the same or longer duration.."
In typical Amateur service, most operation falls into the "ICAS" category. MANY tubes will last YEARS within the "intermittent" signature.

AND, some tubes are more linear and reproduce lower IMD at higher plate voltages than the "sheets" prescribe.
813's are virtually interminable even at 2500 V!  ;)

You're in the right place to learn about tubes and all things AM. Use the SEARCH feature on this site. There is a wealth of information here, much of which cannot be found elsewhere. This site is a tremendous resource on the Web. The membership is diverse and helpful. I think you'll find a welcome feeling here, as I have. I'm glad I was able to be helpful to you. :)


Don

Yes, agreed!  

in·ter·mi·na·ble
adjective

seemingly endless, endless, never-ending, unending, without end, nonstop, everlasting, ceaseless, unceasing, incessant, constant, continual, uninterrupted, unbroken, sustained; monotonous, tedious, wearisome, boring, long-winded, long-drawn-out, overlong, rambling, meandering, laborious, ponderous

Usage:

"Last night on 3885 the Tron made an interminable [longwinded] old buzzard transmission on his virtually interminable [everlasting] 813s!"  ;D

T

Running a DX-100 with 1 6146 final is not such a good idea, it beats the snot out of the tube and doubles the plate to plate load impedance on the mutilators. That raises the distortion and voltage swing, the mod iron doesn't like excessive voltage peaks.

Matched tubes? An audiophool might buy a matched pair of KT88s if he doesn't know his amp has a balance pot, but I've never seen a DX 100 with one.

Speaking of DX100s, if you listen carefully to 3885 when the early morning mist rises from the pond, you might hear the melodic sound of wind chimes off in the faint distance......

Thats quite a message.


KLC

The effects of "modulator looking into much higher impedance" etc. as mentioned previously, are important considerations that I'm still looking into.  As far as the tube goes, the tube manual list the specs, which can be measured. As to tube "matching" it seems you don't understand the concept, it was not invented by the
"audio world", but long ago. you mention the balance pot, which clearly shows the importance of the tube currents,etc. not only is it important that the tubes are at least not badly "mis-matched" but the tube circuits must "match", they design them that way. If one tube draws much more current than the other it will be operating past its maximum ratings. especially as in the DX-100 which runs the tubes at maximum ratings.
the entire tube circuits including tubes should not be badly "mis-matched". this is all "measurable".
I hear many DX-100's sounding great on the air, but never any of your "windchimes",
If your hearing things, they say that's a bad sign.
Thanks for your comments and advise, Thanks everyone..
73

Thanks to everyone, this is a Great site !
Since its mentioned in the old ARRL handbooks, and other books etc. as common practice especially for the
Novice class, to run one tube in many transmitters, I was simply wondering if I could do that in my DX-100,
it seems the concenses is you can....but its not a good idea for many reasons.
"matching" tubes was one thought but more importantly, I could test tubes at full power and compare them.
my tubetester doesn't test them at full power, I don't know of any tubetester that does.
The best thing that came out of this for me is that I learned more about measuring plate dissipation,etc.
Thanks again, I'm preparing my next question and its not going to be such a simple one as this was...…
73

You have NEVER heard the windchimes?????    keep listening......   

Not everyone has a  S 19 to hear the voice in the wilderness.

KLC

Ah yes, good old Corky. As a yut, once you encountered him you lived in fear with the need to deal with him for radio stuff. Was he active on the air?
Carl

Melodic I think not :D :D I have heard those chimes countless times and they were filled with teeth grinding blackboard screeching IMD distortion and I really liked it ;D ;D ;D Many of us in the northeast, have our own chimes that we ring out on occasion. In about 15 years when most of the old timers like me burn out, the chimes will only be heard on some distance shore, where hams never die, but just smell that way :P :P :P  

The power transformer will love you, not so much with the mod iron.
Regards,
Gary

fear of the FCC and other things.
http://www.antentop.org/w4rnl.001/ugger.html

Hi Carl -

So you knew Corky too?  Any stories about him or the store?

He was a legend for sure.  He owned a Collins 75S3B, 32S3 and 30-L1 when they first came out.  He was Collins' biggest advocate.   Whenever anyone axed him his opinion about a radio, he would tell them to get rid of all the bullshit and buy a Collins station. He was right when it came to ssb stuff

I remember a day in 1967 when he was smiling and said, "only one more payment to the Old Man and the S-Line is all mine!"

He was very popular on 20M ssb with a large group early in the morning before his drive to work at Hatry's.  I heard him on a few times and he was the channelmaster from E. Granby, CT on a lake. He had a TA-33 tribander.

I remember taking my Novice CW test from him.  I met Ed, W1RFI in 1965 thru Hatry's who became a Novice buddy and later met some FB girls from Manchester thru him. There are so many stories to tell.

I had a paper route so had lots of money to buy rigs and kept trading in and out there. One time I bought 170' of Channelmaster telescoping steel mast. I was so dumb (or was it motivated?) I was about to try carrying 17  10' pipes to the bus stop on Main street and get on the bus to Windsor. Corky was leaving, saw my plight and gave me a ride home with the masting in his station wagon.


Another time a ham who just bought an S-line from him said he couldn't get on the air because he couldn't afford the power supply yet. Corky suggested that he homebrew it. The guy acted insulted and insisted that he didn't build his own refrigerator, so why should he build his PS? Quite the analogy.

One time I bought a Gotham vertical from him - my first antenna as a Novice.  I filled up part of a logbook calling CQ without a single reply. I had a ham listen for me 12 miles away and he heard nothing. I brought it back to Corky who axed me where I got that piece of crap?  He had forgotten he sold it to me a few weeks previous. He showed me how to make a coaxial pigtail for a dipole and the whole world opened up with 599s from IL that night on 40M.  BTW, the Gotham vertical was grounded at the top due to my installation error.. another story. It may have worked otherwise.

Corky's health slowly deteriorated... I think asthma from smoking those cigarettes and diabetes. He axed me a few times to go across the street (High St) and get him some sugar donuts.  Poor guy. After the Hatry's move to Murphy Rd he lasted a few more years, maybe 68 years old? and that was it.

He was licensed as W1KXM in the early 30's and lived in Windsor, not far from my QTH I found out later.

Hatry's on High St. was a magical place. I have never seen any pictures of it, unfortunately.  I'm sure they are around somewhere.  The "Old Man" Mr. Hatry, has quite a radio background himself.

Info on early Hatry:
http://www.sparkbench.com/homebrew/Hatry/hatry.html


T

I just discovered the article in "Don's Tech Talks" (K4KYV),
 titled  :   "Modulation Transformer Impedance considerations",  right here on this site, very interesting and seems very relavent to the subject. who knows what else I'll find right here! this is a great site.
73, KG5WWK