[Amps] CW and High Voltage

R.Measures r at somis.org
Sun Sep 4 13:41:12 EDT 2005


On Sep 4, 2005, at 9:13 AM, gdaught6 at stanford.edu wrote:

> On 4 Sep 2005 at 7:17, R.Measures wrote:
>> On Sep 3, 2005, at 10:53 PM, Phil Clements wrote:
>
> < snip, snip : other attributions >
>
>>>>>> Cutting the drive back too much will indeed cause a good size
>>>>>> mismatch
>
> < more snips >
>
>> Most of the manuals that I have read give instructions that say to
>> reduce drive during tuneup.  Do you agree with this procedure?
>
> In my opinion, we may be addressing what shouldn't be a problem.
> What I mean is this:  the FIRST TIME I tune a new (or modified) amp,
> I believe it's prudent to start with reduced drive, so that I don't
> make a flash-bulb of the control grid (and/or screen grid) and seek
> the proper settings for the tune and load capacitors.

George
-  When an amplifier is tuned far from resonance,  grid-current and, 
for a tetrode or pentode,  screen-current is virtually zero.   In a 
properly designed amplifier, the grid and screen are fused with a 
frangible element.

> Then the drive
> can be increased, with the capacitors adjusted to get the designed
> value of power out, and all meters reading the proper numbers.

Agreed, but I skip the first step.

>  I
> increase the loading a tiny bit until the output drops just
> perceptibly.  Then, I write down the settings, and I can go to
> another band, and perform a similar exercise.

Good plan.  I mark each band with a different color wax pencil.  7255 
is not feces-brown, although it probably should be.
>
> Now I can return to the original band, duplicate the settings and
> transmit!  I know that I'm matched.  There's certainly no need for
> reduced drive.  In fact, there's no need for "tuneup" if I'm using
> the same antenna, etc.  At most, I'll twiddle the "tune" knob to peak
> the output if I've gone from 7.005 to 7.255 MHz or some such within
> the band frequency change.  (Although I don't know why anyone would
> want to be on 7.255 8>)

Lately it has been semi-dead due to el stinko propagation.
>
> If I want to reduce power on CW, I'll turn down the "RF out" on my
> transceiver.  On SSB, the same thing works, but the "Mic gain" is my
> choice.  There's no need to redo the whole tuning thing.

Another good plan.
>
> Does this seem to be a reasonable approach?

Yes

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org



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