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Broadcast Audio from your DX-60




 
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Author Topic: Broadcast Audio from your DX-60  (Read 33311 times)
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fg5fc
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« Reply #50 on: January 22, 2015, 03:02:58 PM »

While the 4D32 seems close to a twin 6146 in one bottle, there are differences.
The 4D32 has much higher bias and screen voltage then the 6146 has in the same class of service.
120 volts on the screen for the 6146 I think, and 300 on the 4D32.
Much less grid bias and current on the 6146 also.

I suspect the 4D32 wants a much stiffer modulator.

This modulator works very well on a pair of 4x150/4cx250b's though.
A very clean 75 watts out at 1200 volts on the plates, likely good for 150 watts carrier at 1800 to 2000 volts.

Anyone ever try it with a pair of 6146 tubes? Knight kit 150 type rig?

Hello Brett
I'm a little bit surprised that WA1QIX does not do any comments on your results, you have made a lot of job, a lot of comments in building a nice screen modulation project!

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N2DTS
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« Reply #51 on: January 22, 2015, 03:55:33 PM »

Its an old thread from 2011.
I just wanted to update it in case anyone else wanted to try the circuit, which works great within its limitations.

And I think some tubes just will not sound clean no matter how you modulate the screen.
I lump the 813 and the 4D32 into that category, the 6146 and the 4x150 seem good.
Maybe its tubes that use lower screen voltages that work best, and with this circuit, ones that do not pull much current on peaks and some tubes likely do not track plate current with screen voltage well.

From what I see, it seems like the output impedance is whatever the cathode resistor is?
In this case, 39k ohms?

In my tests, the 4D32 was flat topping easy unless run at very low power outputs (5 watts).
The solid state modulator worked fine with the 4D32's, even 3 of them at once.

I am sure Steve could design a simple mosfet circuit with a real low impedance that took little drive and was good for all sorts of voltage and current.
There are some amazing devices out there these days.

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WD5JKO
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WD5JKO


« Reply #52 on: January 22, 2015, 06:25:39 PM »


Brett,

    Take a look at the "Power-Drive" circuit at the following web site:

http://tubelab.com/articles/circuits/power-drive/

   The 2SK2700 FET is what the guy uses. Look at the gate of FET, and the battery used for bias control of the output tube. Just turn that battery around to set a screen voltage to the RF amplifier.

Jim
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N2DTS
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« Reply #53 on: January 22, 2015, 08:15:46 PM »

Yes, something like that would work, somehow.
The voltages are not excessive on many tubes, 100 to 200 volts plus the swing.
The W2IMX solid state design seems good, low parts count, only the screen power supply needed (no bias) and line level input.




Brett,

    Take a look at the "Power-Drive" circuit at the following web site:

http://tubelab.com/articles/circuits/power-drive/

   The 2SK2700 FET is what the guy uses. Look at the gate of FET, and the battery used for bias control of the output tube. Just turn that battery around to set a screen voltage to the RF amplifier.

Jim
Wd5JKO

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N2DTS
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« Reply #54 on: January 22, 2015, 10:24:26 PM »

Waveforms from this modulator, 80 watts carrier out of a pair of 4x150's at 1300 volts, off the IF out of the homebrew rx.


* P1220181.JPG (3754.29 KB, 4288x3216 - viewed 334 times.)

* P1220185.JPG (3831.38 KB, 4288x3216 - viewed 305 times.)
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N2DTS
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« Reply #55 on: January 22, 2015, 10:26:15 PM »

the edge of the negative peak limiter at 40 Hz:


* P1220184.JPG (3849.44 KB, 4288x3216 - viewed 370 times.)
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flintstone mop
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« Reply #56 on: January 23, 2015, 05:36:41 PM »


The Triangle looks almost shweeet Brett,
You gotta winner!!!

Now, my question is, once the hairy adjustments are made to get the screen modulation perfect; what happens when you QSY, and go through the peak the grid, and dip the plate of the finals?? The screen modulation adjustments never change??

Fred
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Fred KC4MOP
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« Reply #57 on: January 23, 2015, 07:52:28 PM »

I change bands all the time, all you really need to do is load the rig up to maximum power output, then increase the loading till power falls off quite a bit, redip the plate tuning and away you go.
The amount of loading sets the peak power, you can adjust it for 100% both ways and get a bit more carrier output at lower plate current, or gobs of peak power with a lower resting carrier.

I like to do it the way I do it, instead of tuning up for full power then turning things down as there is less stress on things, and less tuning at full power.
You have to be sure the tank coil is cut to give full power output with plenty of adjustments left (tuning and loading) to adjust things to get good peak power.

Grid drive always stays on the low side, the only trick (initial adjustment) is the resting carrier level.
Once that is figured out, its only plate dip and load, over load till the power falls off about half.
A peak reading watt meter is a must, mostly for looking at those crazy power peaks.
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N2DTS
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« Reply #58 on: January 23, 2015, 08:09:45 PM »

I will be running the modulator on 40 tomorrow I hope, about 70 watts out from the pair of 4x150's.
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N2DTS
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« Reply #59 on: September 28, 2015, 11:25:35 AM »

Just an update about this great circuit, I bumped up the voltage to the pair of 4x150's (4cx250b) to 1600 volts and run 200 watts carrier out of the pair with this modulator circuit and it sounds and works great.
200 watts carrier and 800 to 900 watts pep.
Some dx60 that is!
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VE3AJM
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« Reply #60 on: September 28, 2015, 11:40:59 AM »

Was that the DX-60 that you were on yesterday on 40m with Russ WB3FAU? It sounded good.

Russ sounded good too with his Globe King 500, with the terrible? single ended 6L6 driving class B 811A grids through a driver transformer?

Al VE3AJM
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N2DTS
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« Reply #61 on: September 28, 2015, 12:02:25 PM »

Yes, I was running this modulator, into a pair of 4x150's at 200 watts carrier output.
Russ always seems to sound good.
Love the WRL power hum in the background of the audio, sounds powerful.




Was that the DX-60 that you were on yesterday on 40m with Russ WB3FAU? It sounded good.

Russ sounded good too with his Globe King 500, with the terrible? single ended 6L6 driving class B 811A grids through a driver transformer?

Al VE3AJM
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Donnie SWL
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« Reply #62 on: September 28, 2015, 12:54:49 PM »

I guess you could run the plate up to 2000 on the 4x150 in screen modulation??The only tube i've seen eimac rate for screen modulation is the 4cx5000 an they run it at full plate voltage 7500 ....
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VE3AJM
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« Reply #63 on: September 28, 2015, 02:03:02 PM »

Its interesting to me that the hum wasn't really noticeable listening on two receivers. R-390a at 8kc and Kenwood R-5000 at 6kc.

That being said, I've heard this 120hz hum on some WRL gear before. Including txs like some Globe Champion 300 and 300as, besides some GK500s.  I'm curious If this hum issue is VFO based or something in the power supplies with inadequate filtering, ground loops or something else in the audio.. Is there a consensus on it.

Al VE3AJM
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N2DTS
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« Reply #64 on: September 28, 2015, 04:43:55 PM »

Well, the audio chain has to go down to 60 Hz...

Much of it is the steel cabinet vibrating I think, at least in some rigs as Russ has said he improved the power supply filtering and the DC is clean.

I think it sounds cool, along with the big thunk on key down some have.
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VE3AJM
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« Reply #65 on: September 28, 2015, 05:00:52 PM »

My 390a audio comes off the detector feeding a high quality PP tube amp. So hearing 60hz is no problem.

Russ was 80 db signal  ie. a very strong signal at the time.

Al VE3AJM
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N2DTS
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« Reply #66 on: September 28, 2015, 09:13:01 PM »

Maybe he moved the mic away from the transmitter, or was running something else?
He always has enough audio, and it always sounds clean to me.

You could likely run the plate voltage up to 1800 volts on the 4x150's, its all about plate dissipation.
With the 4x150's you can run into problems with reverse screen current.

I just made note of how things are running, ran the rig into the dummy load to prevent the swr from changing the power readings.

1800 volts on the plates,
260 ma cathode current,
160 watts out (carrier),

So:
470 watts in,
160 watts out,
308 watts dissipation out of 500 available.

With a 1.4 to 1 swr on the antenna, the power reads 200 watts carrier...

1800 volts is as high as that power supply goes.

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Steve - K4HX
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« Reply #67 on: September 28, 2015, 10:32:50 PM »

Many were pretty light on the filter cap. IIRC some of the Kings used 4 uF.
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N2DTS
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« Reply #68 on: October 10, 2015, 10:55:02 PM »

Worked him again today, the hum is there, quite loud, and shows on the sdr.
I had him turn the mic gain down and the hum was still there.
N2LJO joined in on his Globe King 400 and said his used to hum before he put a huge filter cap in.

There used to be an add in the old QST's about how everyone could tell when the guy was using the globe king.
W4TFA, C.L.Meistroff, said the boys know when the unmodulated carrier is on, the Globe King is on the air.
Not a hint of TVI either.
He said his Globe King really gets out!

I think they sound great stock, the background hum just makes them sound very powerful.
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