Final loading for Heathkit dx-60

[wa5ddz]

 Hello everyone, and all the ships at sea.
What factor(s) would cause my Heathkit DX-60 not to produce the highest
output at the lowest final dip? A slight increase in the final loading produces
the highest output - not the lowest dip. Or do I just live with it.  Am and cw
both work. Thanks in advance for any and all info.

[The Slab Bacon]

A dx-60 is like any other transmitter. Start with loading at minimum, adjust for tune for your lowest dip. Then advance loading for desired output. Redip again and it is what it is. the plate current SHOULD rise as you increase the loading.

For phone, you have to increase the loading until the output starts to fall off somewhat so you are loaded heavy enough to make the voice peaks.
this is true for any scream modulated transmitter.

At this point the dip will usually be very small.

[kb3ouk]

Something that also might clear things up some is that the amount of meshing of the loading cap is inverse to how heavily loaded the final is, meaning the higher the capacitance, the lower the loading. To get heavy loading, you need less capacitance. And in some transmitters, the plate dip does not match the point of maximum output. If I need to reduce power somehow and there is no other power control on the transmitter other than the loading control, I will load the final a little more then redip the plate.

[Pete, WA2CWA]

If you're trying to lower the power output for whatever reason, it's probably better to reduce the screen voltage then detuning the final tank circuit of the transmitter. Something similar to this should work fine: http://www.amwindow.org/tech/htm/drivepot.htm

[kb3ouk]

Well, in my case, that would've been impossible since I was working with triodes.

[Knightt150]

Maybe I can help in a screen modulated transmitter like the DX 60 you do not dip the final and increase the load. You tune the plate and load for max RF out. Put a SWR POWER meter in line to the antenna and adj for max RF out.

I have in all my years working with screen modulated transmitters never really figured out why this is so, maybe someone can explain the techinal reason .

John W9BFO

[kb3ouk]

It might be because a screen modulated final acts more like a linear amplifier, as you modulate it the efficiency increases to make the peaks. And that is also how you tune a linear, peak the plate and load for max output.

[W3RSW]

Your symptoms also might be a result of improper neutralization of the final.

[ke7trp]

Thats what I was thinking. I think he is saying that has he comes out of the dip, He gets higher output.

[The Slab Bacon]

But.......... is he actually coming out of the dip, or is the plate current just rizing from increasing the load ? ? ?

With a screen mod rig, you have to load it heavy enough to drop the plate efficiency to somewhere around 33% at resting carrier so it is loaded heavily enough to make the audio peaks. (At this point the "dip" will be very small) This tunes the PI network to the impedance of the voice peaks and NOT the carrier parameters. Yes.........basically the same way you load a leanyour yamplifier.

If you tune for max blowsomke at resting carrier you wont have enough ass left to make the audio peaks.

Scream mod rigs have kinda become somewhat a specialty here since my big rig is a scream modulated 4-1000A That I designed and built 12 years ago.
It breaks all of the rules and stigmas associated with scream mod rigs and is NOT controlled carrier, just a scream modded class-C final! It makes BIG power and Big audio. I originally built as an "I told ya so" experiment, and It worked so well that I kept it as my mainstay transmitter. It, however loads very differently from a standard scream mod rig.

[kb3ouk]

So to really tune a screen modulated final the right way, you probably need to know what the normal plate input power would be, next dip the final and lod for max output, but then start loading heavy till you get to 33% efficiency, and redip the plate if there is any dip left at all.

[The Slab Bacon]

So to really tune a screen modulated final the right way, you probably need to know what the normal plate input power would be, next dip the final and lod for max output, but then start loading heavy till you get to 33% efficiency, and redip the plate if there is any dip left at all.

Dont make it harder on yourself than you have to, but that would be the textbook way to do it. A simple scope on the outpoot, viewing the waveform (not a trapezoid) makes it real simple. Just load it till the carrier outpoot starts to fall off a bit and the audo peaks come up to max. Check the "dip" afterwards and yer good to go. It only takes a few seconds that way.

[wa5ddz]

 Thanks for all the info. Since I have 3 of the dx-60's I'll try the different
methods. Maybe one will survive !  I have never tried using a scope for
this type of tuning. I have a B&K 10 mkz model 1471B. It may suffice. After the smoke clears,
As Arnold said " I'll be bock ".
   Cemo for the next three days, TU. WED. THU. That kind of puts me out for
a few days. Thanks again for the help 72 Bruce