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Broadcast Audio from your DX-60




 
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Author Topic: Broadcast Audio from your DX-60  (Read 32461 times)
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Knightt150
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« Reply #25 on: February 03, 2011, 03:00:34 PM »

Hello: I have two KNIGHT T150's and have spent a lot of time on trying to get 100% modulation (with out distortion) out of the rigs. I can do almost 90% but after that its down hill. Has anyone every done this or can it be done with the DX 60 mods.

John W9BFO
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steve_qix
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« Reply #26 on: February 03, 2011, 03:39:55 PM »

Hello: I have two KNIGHT T150's and have spent a lot of time on trying to get 100% modulation (with out distortion) out of the rigs. I can do almost 90% but after that its down hill. Has anyone every done this or can it be done with the DX 60 mods.

John W9BFO

It's a very similar setup, so I would recommend this circuit.  I don't recall the modulator tube used in the T150 - you may or may not have to change that as well, but if the tube is similar in its characteristics, probably not!

Regards,

Steve
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N4LTA
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« Reply #27 on: February 03, 2011, 05:32:04 PM »

Slow day today at work. I layed out a PC board for Steve's circuit. May build it and try it in the next few weeks.
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ve6pg
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« Reply #28 on: April 11, 2012, 06:14:29 PM »

..steve...do you have a dwg of your mods fer the dx60?

..tim..

..sk..
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...Yes, my name is Tim Smith...sk..
steve_qix
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« Reply #29 on: April 11, 2012, 06:21:16 PM »

..steve...do you have a dwg of your mods fer the dx60?

..tim..

..sk..

Yes, in the first entry of this post (on the first page of the post, this is page 2).  The schematic should be there, etc.

Let me know if you don't see it, as there could be an error.

Regards,

Steve
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ve6pg
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« Reply #30 on: April 11, 2012, 07:23:26 PM »

..thanks steve, got it now...maybe a dial-up error...is this the same type of mod bud did to his drake?..

..thanks agn..
..tim..

..sk..
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KM1H
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« Reply #31 on: April 11, 2012, 08:00:18 PM »

The zener string bypass is non polarized?

Carl
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steve_qix
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« Reply #32 on: April 12, 2012, 06:48:26 AM »

The zener string bypass is non polarized?

Carl

In my own transmitter it is non-polarized, but there is no reason why a polarized capacitor could not be used, with the positive terminal connected to the cathode.
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Rob K2CU
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« Reply #33 on: April 12, 2012, 08:28:11 AM »

Great circuit, Steve.  The cathode follower driver provides a real low impedance supply for the screen. I would only suggest adding a separate filament transformer for the 6DE7. The spec is a max peak cathode to heater voltage of 200V (plate 275V). And though a tube may start out handling the voltages, it will be stressed and may eventually fail. If you can loose the first half with its cathode essentially at ground, and make up the gain elsewhere, so much the better.

JJ had this issue with his neat dual 6AQ5 series modulated QRP transmitter.
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steve_qix
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« Reply #34 on: April 15, 2012, 08:07:18 PM »

Great circuit, Steve.  The cathode follower driver provides a real low impedance supply for the screen. I would only suggest adding a separate filament transformer for the 6DE7. The spec is a max peak cathode to heater voltage of 200V (plate 275V). And though a tube may start out handling the voltages, it will be stressed and may eventually fail. If you can loose the first half with its cathode essentially at ground, and make up the gain elsewhere, so much the better.

JJ had this issue with his neat dual 6AQ5 series modulated QRP transmitter.

The voltages are the same as the original DX-60 circuit.  I don't know the exact DC voltage on the 6146 screen, but I don't think it's all that high.  I did question this also, but figured folks have been using DX-60s for around 50 years, and I haven't heard about a lot of problems with the 6DE7 breaking down - heater to cathode wise, so thought I'd just stick with the exiting voltages  Wink
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k3vyy
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« Reply #35 on: February 06, 2013, 08:18:07 AM »

Does the 250k pot need to be a 2W version, or will a 1/2 watt suffice. Just started on the mod and cleaning the old components out of the DX-60 I acquired.

Dick, K3VYY
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steve_qix
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« Reply #36 on: February 06, 2013, 09:39:40 AM »

Does the 250k pot need to be a 2W version, or will a 1/2 watt suffice. Just started on the mod and cleaning the old components out of the DX-60 I acquired.

Dick, K3VYY


A small pot is fine for that application.

Regards,

Steve
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k3vyy
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« Reply #37 on: February 14, 2013, 08:46:47 AM »

Thanks Steve, 73
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KD7EDW
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« Reply #38 on: May 14, 2013, 06:58:43 PM »

How do you drive this?  Do you use a mixer board or the just  pre-amp circuit listed on your class-e website?

Fred
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W4RFM
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« Reply #39 on: May 18, 2013, 12:14:58 PM »

Hey Steve,
That sample is some excellent audio.  I may hit the next fest and snag me a -60 and try this mod. Very nice.
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BOB / W4RFM
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« Reply #40 on: May 19, 2013, 08:18:29 AM »

I use my shack audio system - same one is used for all rigs.  This is really the only way to go if you have more than one transmitter.  Just build up an audio system with EQ, peak limiting, etc., make it line level out and then you can use it with anything.

That DX-60 modification is really just a generic, low power screen modulator that could be used with anything.  An easy home brew project, particularly if you just want it on a few bands - in case you have trouble finding a DX-60 at a flea market, that is.  There are a number of other screen modulated rigs that were made, and the modification would work just as well there!  Cheesy
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N2DTS
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« Reply #41 on: January 20, 2015, 12:12:50 PM »

I built the circuit as a standalone modulator and it works real well if you add feedback from the screen output to the 2nd stage audio amp cathode with a 1 meg resistor and a .003 uf cap.

I added a d104 input but it also has a line level input.
The negative peak limiter works well at 400 Hz but looks very nasty at 40 Hz.
The waveforms look very good at 40 Hz to about 80% negative  and then get ugly when the NPL works.
Not sure that is a problem in the real world or not.

The circuit worked well into a pair of 4x150's running 100 watts output.
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WD5JKO
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« Reply #42 on: January 20, 2015, 01:51:41 PM »

I built the circuit as a standalone modulator and it works real well if you add feedback from the screen output to the 2nd stage audio amp cathode with a 1 meg resistor and a .003 uf cap.

The negative peak limiter works well at 400 Hz but looks very nasty at 40 Hz.
The waveforms look very good at 40 Hz to about 80% negative  and then get ugly when the NPL works.
Not sure that is a problem in the real world or not.

The circuit worked well into a pair of 4x150's running 100 watts output.

    Brett,

    As you sweep down in frequency your NFB is going away causing a low frequency gain rise. Also audio that goes through a negative peak limiter (NPL) and is then fed back in a NFB circuit poses a problem since the NPL effect is a distortion that we want to keep. For this reason in some of my gear with a high level NPL, I limit any NFB around that stage to about 3 db (that be 0.707 in volts), and then see if I can add more without making things worse..

   That .003uf capacitor has about 1.3 meg ohms capacitive reactance at 40 hz. Maybe change that to a 0.01 uf or perhaps 0.05 uf and try that test again.

Jim
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N2DTS
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« Reply #43 on: January 20, 2015, 02:03:53 PM »

Great idea, I will try that.
The original circuit had NO feedback, at least it was not shown.
That might depend on the tube the circuit is modulating, I was doing a pair of 4x150's not a single 6146.

I only added the feedback to eliminate a lot of distortion when I had the normal amount of grid drive to the final, running the grid drive real light (1ma) had it sound ok, but the feedback made the grid drive not matter much.

I suspect the negative peak limiter just does not work well at low frequencies.
I should test just where it starts to fall apart and take pictures.

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N2DTS
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« Reply #44 on: January 20, 2015, 08:29:24 PM »

I put a .01 7kv cap in and it still looks unclean.
Sounds great tho.
It starts getting funky looking at about 100 hz, but only when it gets into the limiter, and you can not see anything like that on voice.
This circuit works very well for a little tube circuit.
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flintstone mop
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« Reply #45 on: January 20, 2015, 08:33:30 PM »

Thanks Steve
A very interesting thread about screen modulation. Seems to be a revival for the ease of obtaining hi-fi audio and plenty of positive peaks without the heavy iron and expense of modulator tubes.

Our own RF genius, Timtron, made some changes at WBCQ and got a military transmitter on the air and achieving out-of-this-world-audio. He is exciting this monster transmitter with a Viking II with about 25 watts. The Viking II was missing its modulator.
In Tim's words, " I decided to reserect it as a continuous duty cathode follower screen modulated transmitter. It is good for a maximum outpoot of 25 watts." He bypassed the 6CL6 and 6146 in the Viking II. The first stage of amplification is a PL-172/8295 tube in the IPA of this transmitter

It's unbelievable what this guy can do. He told me that this arrangement would sound much better than a commercially available PWM rig. Before the filters stop high frequency audio from being transmitted, the 'exciter" was good from 5hz to 15kc.....FLAT!!!
Fred
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Fred KC4MOP
N2DTS
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« Reply #46 on: January 20, 2015, 08:49:26 PM »

True.
35 years on AM and I never tried it till now, and boy, it sure works well.
No phase shift and other weird stuff that goes on inside transformers, no digital trash or pulses to be filtered out, just class A audio with no real reason for a restricted frequency response.

I was testing at 20 Hz 100% modulation today and nothing was going to blow up, and the waveform looked very good.
And the peak powers a screen modulated rig can hit is very high, I run my big rig at about 250 to 300 watts carrier and it hits 1500 watts pep very easy at 80% negative modulation.
Mic phase really makes a huge difference, no phase shift.
No transformers from mic to antenna...

I also like that most circuits have a power control, just dial up whatever power output you want.
Its a LOT of fun to play with.
 
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DMOD
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« Reply #47 on: January 20, 2015, 09:45:24 PM »

There are quite a few approaches to modifying the DX-60 modulator.

N1UVI also has a HIFI screen modulated circuit as well:

http://amfone.net/Amforum/index.php?topic=30451.0


Negative peak clipping and power control can also take the following form:

Phil - AC0OB


* DX-60 Modulator Schematic NG For AMFONE.pdf (27.69 KB - downloaded 176 times.)
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N2DTS
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« Reply #48 on: January 21, 2015, 10:14:47 PM »

I tried it, it does not sound good at all with a 4D32 for some reason.
It only sounded somewhat clean at very low power levels (5 watts).


I bet this idea would be rocking with a 4D32.  I'm envisioning about 25 maybe 30 watts of carrier with extreme hi fi. 

Man I love learning! 
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N2DTS
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« Reply #49 on: January 22, 2015, 08:22:32 AM »

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?
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