pi-network to link-coupled PA grid tank

[KC2ZFA]

consider an exciter with pi-net in its PA driving an amplifier using B&W JVL coils (center-linked, variable link) in the grid circuit. The amplifier's input link is directly grounded on one side (coax input).

How do we tune this combo ?

Do we set the JVL link (half-in to begin with) and then dip the exciter final while increasing the exciter loading until we have the desired amplifier grid current ? I'm guessing that when the correct amplifier grid current is reached then it should be at its peak when the exciter final is at its dip.

confused 

[KM1H]

The last time I did that was with a Viking I into PP 250TH's in the late 50's and just as you described.

Its a lot of work the first time and it helps to make a chart so its a lot easier in the future. It also soured me on plug in coils forever as I love to move around. Even the pair of HT-9's here are parked on one band each.

Carl

[KC2ZFA]

thanks Carl.

It does take a lot of work to tune with 4 variables to fiddle with
(tune/load in exciter and link-position/grid-tuning in amplifier).

I've already destroyed a 6146 learning how to do this. I've stolen
the tuning chart assembly from a BC-375 tuning unit to use for
logging.

Peter

[n2bc]

I guess I cheated.  Setup was a Ranger driving a pair of 4-400s, link coupled to the '400 grids.

Step 1, eliminate the tune & load of the Ranger. Reduce PA plate voltage, drive PA with a sand-state transceiver with a few watts, insert SWR bridge between exciter & PA, tune PA grid for best match. Gradually increase drive for proper grid current, record PA grid tuning settings.

Step 2, replace SS exciter /w Ranger.  Set PA, tune Ranger, record Ranger settings.

Step 3, ensure fire extinguisher is ready, crank up the power, record final tweaks.

[The Slab Bacon]

Hmmmm..............

Tune oscilator......
Tune buffer.......
Tune pre driver grid.......  
Tune pre driver plate / driver grid.........
Tune driver plate........
Tune final grid........
Tune and load final plate........
Tune up antenna tuner..........

Someone asks you to QSY 50Kc.............       Priceless! !    

[KC2ZFA]

I think I can handle it...just look at me !

[k4kyv]

Hmmmm..............

Tune oscilator......
Tune buffer.......
Tune pre driver grid.......  
Tune pre driver plate / driver grid.........
Tune driver plate........
Tune final grid........
Tune and load final plate........
Tune up antenna tuner..........

Someone asks you to QSY 50Kc.............       Priceless! !    

But... "For historical reference only.  Nobody uses transmitters to-day that have to be tuned."   

[W7TFO]

Hmmmm..............

Tune oscilator......
Tune buffer.......
Tune pre driver grid.......  
Tune pre driver plate / driver grid.........
Tune driver plate........
Tune final grid........
Tune and load final plate........
Tune up antenna tuner..........

Someone asks you to QSY 50Kc.............       Priceless! !    

It worked very well in the past.  The key, at least as I have found out, is complete metering.  Not one or two switched meters, but one for each parameter necessary when going QSY.

One example is the Westinghouse Navy TBL series TX.  I had two of these back in the 70's and changing frequency was not a big or long deal.

73DG

[KM1H]

However the Navy Radiomen had a tuning chart and just needed a quick touch up

[KC2ZFA]

Step 1, eliminate the tune & load of the Ranger. Reduce PA plate voltage, drive PA with a sand-state transceiver with a few watts, insert SWR bridge between exciter & PA, tune PA grid for best match. Gradually increase drive for proper grid current, record PA grid tuning settings.

neat !...I will have to borrow some sand to try this.

[The Slab Bacon]

But... "For historical reference only.  Nobody uses transmitters to-day that have to be tuned."   

Speak for yourself   



I figgered that post would "stir the pot" a little, and be good for a few giggles   

[k4kyv]

But... "For historical reference only.  Nobody uses transmitters to-day that have to be tuned."   

Speak for yourself   

Isn't that what some QST writer or ARRL official stated recently?  I recall mention of it in an earlier thread (or maybe in a message posted on the AM Reflector), but couldn't re-find it so that I could quote it directly.

[The Slab Bacon]

Isn't that what some QST writer or ARRL official stated recently?  I recall mention of it in an earlier thread (or maybe in a message posted on the AM Reflector), but couldn't re-find it so that I could quote it directly.

You know,
                It's a shame, but that is why so many are terribly intimidated by those 2 large knobs on an amplifier that say "tune" and "load"...............

I had a friend who was willing to pay huge dollars for a "no tune" amp. I openly laughed at him and told him that he must have more money than good sense. I dont remember what the amp was, but it was well over $5large for something like 6 or 700w pep.

I talked him into buying an L4-B and easily and quickly taught him how to tune it up.
He has lived happily ever after. He ended up getting twice the outpoot for 1/3 of the money.

"Dip the grid and peak the plate, watch your finals evaporate!!"   

[WA2ROC]

That looks like a "13 meter rig" to me.....