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Author Topic: Question for the experienced ham  (Read 399 times)
KC9JCH
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Posts: 29




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« on: October 21, 2009, 11:07:18 AM »

If I have a rig with tube finals (FT-102) and a tube amp (SB-200), what is the proper tune up sequence?  Tune rig into dummy load then turn on amp and load amp once the rig is tuned?  All of my antennas are "close enough" to resonant that no external matching network is needed with either this radio or this amp, the one possible exception being 75/80m where my dipole is cut for the phone end of the band.
Thanks,
Tim
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WB2WIK
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« Reply #1 on: October 21, 2009, 11:35:02 AM »

You've got it exactly right.

You can tune the input networks in the SB-200 to emulate a dummy load pretty well (they may already be properly tuned, but if not, you can adjust them), so tuning into a dummy load "barefoot" and then switching on the amp and tuning it into the antenna should be all that's normally required.
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N5LRZ
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« Reply #2 on: October 21, 2009, 11:43:32 AM »

If one reads the polite protocal one sees that the official method is to tune into a dummy load and then switch to an antenna afterwards--to reduce or eliminate QRM.

However let us look at the real world.  Seldom are real world antennas line dummy loads.  If you tune into a theoreticly perfect dummy loand and then switch over to an actual antenna what happens?  Of course your radio is immediately out of tune for the real antenna.

Which is why the majority of amateurs tune directly into the antenna they intend to use on an unused frequecy close to a frequency that they intend to use.  Just remember to tune as quickly as possible to keep the QRM to a minimum.

The dummy load theory is nice on paper but when reality comes around it is completely impractical.
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KC9JCH
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« Reply #3 on: October 21, 2009, 11:49:19 AM »

Thanks,
I agree with the "real world" considerations.  Easy to use the dummy first to get as close as possible then switch.  I can see an endless cycle of tuning the amp then the rig then re tuning the amp...
Now I've got to rig a relay to handle the swithcing voltage of the SB-200...
Tim
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K4DPK
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« Reply #4 on: October 21, 2009, 12:53:06 PM »

Whether or not you use the dummy load method, the very last step should be to key down and make sure the plate tuning is dipped on both the exciter and the amplifier.  

If you do this, the dummy load method is the safer of the two for both.

Phil C. Sr.
k4dpk
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N5LRZ
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« Reply #5 on: October 21, 2009, 01:12:05 PM »

RE DPK...

Actually using modern radio equipment the only tube, and sometimes you do not have to even worry about that with the new semiconductor amps, you have to consider is that big one in the amp.

OOOOh by the way original poster....

When you tune your amp and you get it all set up take a pencil and make a small mark using a referenc point on the various tune dials.  Put the band by the mark.  That way next time you want to tune in that particular band all you have to do is to put the dial reference point on your pencil marks and then go from there.

I mentioned pencil because pencil is not permanent and can be either erased or washed off.
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KB9CRY
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« Reply #6 on: October 21, 2009, 01:26:03 PM »

If I have a rig with tube finals (FT-102) and a tube amp (SB-200), what is the proper tune up sequence?

You have your dummy load on a switch after the amp, right?

You tune through the amp with the radio into the dummy load.  Then tune the amp into the dummy load.  Then switch to the antennas and operate.

A good op never tunes up on the air, especially when you have resonant antennas.  

If you do need to tweak a tuner, then you find a clear freq near where you want to operate.
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W5DXP
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« Reply #7 on: October 21, 2009, 01:26:47 PM »

I would guess that the most experienced hams didn't own a dummy load or an SWR meter when they tuned their Globe Scout, Viking Ranger, DX-40, or Harvey Wells. :-)
--
73, Cecil, w5dxp.com
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K4DPK
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« Reply #8 on: October 21, 2009, 01:27:41 PM »

LRZ:

You don't dip transistor finals?  No kidding?  Smiley

The purpose of my post was, of course, to contribute to the OP's inquiry.  His exciter has tube finals as you can see.

Phil C. Sr.
k4dpk
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K4DPK
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« Reply #9 on: October 21, 2009, 01:36:31 PM »

You may be right Cecil.

Remember when we used 100 watt light bulbs for dummy loads?

Heathkit even suggested using them in some of the early transmitter kit manuals.

OTOH, most of my stuff was homebrew out of economic necessity, and I just watched the next stage grid grid current.

Phil C. Sr.
k4dpk
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KC9JCH
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« Reply #10 on: October 21, 2009, 04:06:54 PM »

KB9CRY asked
"You have your dummy load on a switch after the amp, right?"
Not exactly is the answer.  I have a Palstar antenna tuner between the amp and feedlines, the bypass position on the tuner goes to the dummy load.  I bought the tuner a couple of years ago when I was using mainly non resonant antennas.  I had used a long doublet fed with twinlead for some time and had tried to get a horizontal loop to work (with poor results) so the tuner was an absolute necessity.  I have since built a 5 band hex beam and hung dipoles for 40 and 80m, so the tuner is really only used to clean up the swr at band edges.  Most of the time I just put the tuner switch to the direct setting and skip the tuner as the SWR is low enough to not cause problems except on 75/80m where my dipole is cut for the phone end of the band.  None of this is new, though.  The part I wasn't sure about was tuning a tube final exciter into an amp, which I had not done before.  The FT-102 is new to me, great old rig, sounds spectacular.  The only problem I may have is that it will easily overdrive the amp as it puts out 175 to 180 watts, So I'll have to leave the tuner in line as it functions as my watt meter and tune the rig up then dial back the drive to something the SB-200 will digest.  I think I'll give this all a shot after this weekend's craziness is over and things are quiet again.  Thanks all for the advice.
Tim
Good luck in the contest!
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KB9CRY
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« Reply #11 on: October 22, 2009, 02:40:55 PM »

To JCH:  I too have a tuner after my amp, but I only have it in line for the wattmeter in it.  All of my antennas are resonant so no need for tuning them.

To LRZ:  If you have decent antennas that do not drift when power is applied, most radios and amps can handle of little of the real world situation. There should be no need or it should be avoided whenever possible to tune up on the air.  That is just needless QRM; you may not hear anything on a frequency but someone somewhere else might hear you.

So again, avoid tuning up on the air whenever possible.

All good radio ops do this; using a dummy load.
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