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Author Topic: Single 304TL Final Modulated by P-P 813's  (Read 25347 times)
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DMOD
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« on: October 28, 2014, 01:01:06 PM »

I am in the process of designing a 304TL RF stage and working on the PI network.

Why 304TL's and 813's? Because they are burning a hole on my power tube shelf and are asking why they are being ignored?  Grin

I am trying to locate some load data for the 304TL's for either the "Resonant Load Impedance," or "Effective Load Resistance."

Bands will be 40, 80, and 160m.

Thanks.





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Rick & "Roosevelt"


« Reply #1 on: October 28, 2014, 01:05:39 PM »

If you can't find anything, four of the internal triodes in parallel would be a place to start for RL @ Ebb.
What, say four 100tL's ?
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RICK  *W3RSW*
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« Reply #2 on: October 28, 2014, 01:22:21 PM »

Now THAT'S what I'm screamin'! I'm right there with 'ya man; been thinking about it on and off for several years now since I probably have all the stuff to bolt one together. Let us all know how it's coming along! BIG STRAP!

73, Phil
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« Reply #3 on: October 28, 2014, 09:46:43 PM »

I was planing the same tube line-up for a xmtr.  I think the 304s are four 75s in parallel.  I was thinking 75m, probably 160m and maybe 40m.

Fred
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« Reply #4 on: October 30, 2014, 03:26:17 PM »

Here is some data from Franks Tubes.

* 304TL.pdf (762.75 KB - downloaded 212 times.)
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« Reply #5 on: October 30, 2014, 06:05:28 PM »

That is an odd one!
The TL/TH tubes look very cool, and really impressive when glowing almost white.
High voltage tubes though, they do not work very well at low voltages.

I never tried 813's as modulators, and never used TH or TL tubes in RF service.
When I had the 30K1 I collected 100TH and 100TL tubes to replace the 75TH tubes that rig used as modulators, and built up a PPP 100TH mod deck which works well but takes a lot of drive power.
800 watts of audio at 2500 volts, 900 at 3000 volts...my bias supply runs out at about 2500 volts.
If you use the TH/TL tubes, you MUST put them behind glass, they will freak people out.
http://n2dts.smugmug.com/Ham-radio/i-z345zrf/X2

Triode or tetrode setup on the 813's?
Is one cleaner then the other?
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VE3AJM
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« Reply #6 on: October 30, 2014, 10:16:06 PM »

Get a hold of ER magazine issue #10 from Feb. 1990.

An article by Bill KD0HG sk on the Kilowatt class C RF deck using a single 304 TL with 2500v on the plate and PI network tank circuit 160-20m.

Al VE3AJM
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DMOD
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« Reply #7 on: October 30, 2014, 11:33:04 PM »

That is an odd one!


Triode or tetrode setup on the 813's?
Is one cleaner then the other?


This will be a triode pair of 813's with the system HV running at about 2200 VDC.
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Steve - K4HX
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« Reply #8 on: October 30, 2014, 11:50:05 PM »

Four 75TLs.

If you can't find anything, four of the internal triodes in parallel would be a place to start for RL @ Ebb.
What, say four 100tL's ?
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W3RSW
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Rick & "Roosevelt"


« Reply #9 on: October 31, 2014, 01:07:31 PM »

Yeah, Fred DZT mentioned that too. I should have guessed better given Eimac's nomenclature starting with 3.

I have one but only two of the triodes light up. Use it as a display.
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« Reply #10 on: October 31, 2014, 04:31:19 PM »

I believe it can still be used at half it's rating; i.e. 152 TL?
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« Reply #11 on: October 31, 2014, 07:25:31 PM »

Chuck, W3FJJ built a final with a single 304TL.
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Rick & "Roosevelt"


« Reply #12 on: October 31, 2014, 07:45:30 PM »

Yes, why not a 152 TL.  Good idea.  Use the dead half as pp neutralization. 15 watts in, 350'watts class C out as per 1/2 of ARRL handbook specs.
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« Reply #13 on: November 01, 2014, 10:57:20 PM »

I used to run a pair of 304TLs modulated by a pair of 833As.  It worked great!   I did run 3kV on everything (common power supply).  Used an 813 to drive the 304TLs.

A single 304TL could be modulated by a pair of triode connected 813s I suppose.  If you want to run a lower voltage, something like 2000V at 400mA may be practical.
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W3FJJ
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« Reply #14 on: November 02, 2014, 04:11:44 AM »

Chuck, W3FJJ built a final with a single 304TL.

I built  a pair of 304TL's in parallel, modulated by a pair of 304TL's
for 160-80 meters, I was hoping it would do 40m too, but
trying to neutralize eight  75t's in parallel is a bear!

A single 304tl in the final would of been plenty enough, but I was
looking for symmetry.

I like the 304TL'S more as modulators, than RF service.
I ran the modulators , AB1,  direct coupled with a pair of push pull 2a3 speech amp.

High Voltage Power Supply, was common capable of 2500v, but  I usually
ran it at 1800 volts,  300 mils, and got 400 Watts out..
No color on the finals and slight blush on Modulators
Just loafing...

Exciter was a DX-100 running 75 watts into the grids..

The rig got dismantled in the QTH move, but all the parts are still here, and
I like to resurrect it.. I am seriously considering changing the finals to a single 3-500z
though, and keeping the 304TL Modulator as is...

Chuck- W3FJJ




* 304TL_RIG.jpg (119.37 KB, 750x1000 - viewed 462 times.)
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DMOD
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« Reply #15 on: November 02, 2014, 11:35:48 AM »

Chuck, W3FJJ built a final with a single 304TL.

I built  a pair of 304TL's in parallel, modulated by a pair of 304TL's
for 160-80 meters, I was hoping it would do 40m too, but
trying to neutralize eight  75t's in parallel is a bear!



Chuck- W3FJJ




Thanks Chuck,

Do you recall the load impedance you used for the pi network?

Thanks

Phil
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« Reply #16 on: November 02, 2014, 01:19:14 PM »

@w3fjj
i have read somewhere that a high µ triode like the 3-500z is not the best to be plate modulated in class c, tell me is that true?
73's from John
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DMOD
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« Reply #17 on: November 02, 2014, 02:11:08 PM »

Get a hold of ER magazine issue #10 from Feb. 1990.

An article by Bill KD0HG sk on the Kilowatt class C RF deck using a single 304 TL with 2500v on the plate and PI network tank circuit 160-20m.

Al VE3AJM

I did and Ray O. said the issue was no longer available but he does have the paper article and will send it to me

Ray is way cool in my book.
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« Reply #18 on: November 02, 2014, 02:34:09 PM »


[/quote]

Thanks Chuck,

Do you recall the load impedance you used for the pi network?

Thanks

Phil
[/quote]

Hi Phil,
I can't find my notes, but I think I used around
3000 ohms with  (Plate voltage/2*plate Current)  Q of 12 as starting point.
 but tweaked it some, since I had roller inductor for L1.
I found I didn't need as much inductance for L1 as handbook
suggested.. So extra inductor in series with roller was
removed..


My Pi-net  was 500pf , 22uh , 2500pf . I used full 22uh
on 160 and about half that on 75meters..

GL   Chuck





* 304TL_TANK.jpg (153.49 KB, 1280x960 - viewed 489 times.)
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« Reply #19 on: November 02, 2014, 04:32:21 PM »

Really nice work Chuck!
Matching meters, and plenty of them!
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DMOD
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« Reply #20 on: November 02, 2014, 06:25:07 PM »

I ran some calcs.

R = (2,200^2)/(2X550) = approx. 4400 Ohms.

R = V/I = 2200/0.545 = 4037.

And from the 304TL spec sheet it looks like the plate-to-plate resistance for AB2 is 5,000 ohms so for single plate the load should be 2500 ohms.

So I think I'll run the Pi-network numbers for 3,450 ohms and see what I get and compare.

Grid bias selected is -380V@70mA (according to tube curves) with 40 Watt drive from an 807. The -450V bias supply is adjustable.
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« Reply #21 on: November 03, 2014, 06:34:35 PM »

For Class C, the plate load (Rp) is approximated by Ep/2Ip.  So, for your parameters ,

Rp = 2200/(2 * 0.545) = 2018
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« Reply #22 on: November 04, 2014, 02:30:07 PM »

Quote
For Class C, the plate load (Rp) is approximated by Ep/2Ip.  So, for your parameters ,

Rp = 2200/(2 * 0.545) = 2018

Thanks Steve.

Quote
And from the 304TL spec sheet it looks like the plate-to-plate resistance for AB2 is 5,000 ohms so for single plate the load should be 2500 ohms.


If the tube has listed an "Effective RF Load Resistance," as is shown for the 6146 for linear service,
http://frank.pocnet.net/sheets/049/6/6146B.pdf, this would make things a lot easier. Cheesy

I know from personal experience the RF load data for the 6146 is right on.

I guess back then the assumption was the circuit designer was going to bring the tube into his lab and run impedance, load, and power experiments to suit the  intended design.
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« Reply #23 on: November 04, 2014, 07:11:08 PM »

That formula has been around for a long time. I'll have to check Terman's book to see if it dates to the 1930s.

Anyway, if you have a reasonable range of adjustment on the variable components in your pi-network, calculating the "exact" load impedance is not critical. You'll tune up the transmitter anyway, and at max power out, the load impedance will be correct.
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« Reply #24 on: November 04, 2014, 07:40:16 PM »

I know this comes from:

R = V^2/2P for class C,

and since Power = Iplate*Vplate

then

R = V^2/2(IV) = Vplate/2*I,

but does it take into account the Rp, the plate resistance of the tube?

The pi circuit will have a bandswitched L and extra C needed, and of course the two variable caps.
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