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Author Topic: Drake twins  (Read 3144 times)
W0NTS
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Posts: 60




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« on: March 06, 2013, 07:35:38 AM »

After a long absence I am slowly getting back into HF. I have become intrigued with those keeping AM modulation alive and well and want to set up a 75M boat anchor AM station. Although I could go with 80#-100# transmitters and receivers I don't feel I want to wrestle all of that weight.
This brings me to give thoughts to the Drake T-4X and R-4B which receive great reviews. Weight wise they are mini boat anchors but in essence should qualify since they utilize tubes. Because I own several Drake SWL receivers I am fully aware of Drake quality. I presently have in storage a like new Drake L-7 amplifier which would mate perfectly with a T-4X. My only concern is with the AM modulation method Drake uses in the T-4X. Does it produce good quality AM modulation barefoot? How about when fed into the L-7 amplifier? I am not of the CB radio mentality which is prone to massively over modulate. I just want AM modulation that is clean and decent, perhaps using a bit of compression. Comments will be appreciated. If comments indicate the Drake T-4X will make a decent AM transmitter, I definitely will consider purchasing the "twins". That said, if anyone has Drake twins (T-4X & R-4B) with AC-4 power supply for sale, please contact me. I would require they be fully operational & cosmetically decent.  Dennis  W0NTS
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KG6YV
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Posts: 505




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« Reply #1 on: March 06, 2013, 10:24:26 AM »

I used a 4-line for AM back in the 90's.  Its narrow audio, almost too narrow for good copy.  The screen grid modulation functions fine, its just that with the 1.2kc filter in the T4X it does not sound like real AM.  Since you have the amplifier I would look around for an old Eico or JOhnson Ranger and run that with the L7 foat about 150W carrier.  A much better AM solution.   

FYI,

Greg
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K8KAS
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Posts: 569




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« Reply #2 on: March 08, 2013, 11:06:02 AM »

I owned 3 sets of B and C twins, and never thought much of their AM quality. I use an AF67 driving a L4B and get nothing but great audio report's. Like someone else said, look for a Johnson Ranger/AF67-68 or Johnson Viking II. Listen on 3880 KHz Sunday at 8 AM  and judge for your self what the best sounding station are running, it's not that hard to hear what works... Denny 73 K8KAS
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WB9GKZ
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Posts: 5




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« Reply #3 on: March 10, 2013, 12:48:26 PM »

I own a Drake B-Line and love the R-4B receiver.  Does a good job on AM in the wider IF filter position.  The transmitter is a different story.  The T4XB uses "controlled carrier" AM modulation.  Barefoot, it doesn't make much of an impression to quiet the frequency.  The unmodulated carrier typically runs only about 8 watts output.  You can talk up the average power to maybe 20-40 watts or so.  It has good positive peak modulation, typically up to the 100 watt mark.  The audio quality is good on AM but there's not a lot of ooomph in the audio.

 I use my amp (an AL-80B) any time I have used the T4XB on AM, it just puts a bigger footrprint on the frequency.  The benefit of the controlled carrier scheme was that a linear was only lightly stressed when put in AM service with the T4XB, since the average power from the exciter is kept low.

Best audio reports came when using a good "crispy" sounding D-104 or Shure 444 mic.  Good luck, the T4XB is not the "best" of AM exciters but it can hold its own when used with a linear. 
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WB9GKZ
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« Reply #4 on: March 10, 2013, 12:55:19 PM »

Just another note.  AM in any of the Drake transmitters is not generated in the balanced modulator and has nothing to do with the SSB filters in the rig.  AM is generated with a screen modulator impressed upon the final tubes.  Fidelity is not restricted in the transmitter's IF.  The AM transmitted frequency response is quite good since the circuit is simple, there are no components in the modulator other than a few coupling capacitors in the speech amp and the screen modulator to restrict response. 

The audio quality is surprisingly good when if you don't run the mic gain up into distortion, flat-topping.  The audio response is very good producing good clarity.  Careful adjustment and use of a scope is advised.  Been there. 
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N3WAK
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Posts: 274




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« Reply #5 on: March 14, 2013, 02:12:40 PM »

Dennis--I have a Drake TR-4CW that I use on AM periodically.  If you haven't seen it, be sure to check out Ron Baker's website, WB4HFN.com.  There are also Drake nets on Sundays and Tuesdays--info on Ron's website.  Jeff, WA8SAJ, has a nice article on improving the AM quality of the TR-4/TR-6, which is posted on Ron's site.  Perhaps one of the net controllers on the Sunday afternoon net could give you some tips about using the Twins on AM. 

Drake radios rock!  73, Tony
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