On Sep 4, 2005, at 9:13 AM, gdaught6@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
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|