[ARC5] Transmiitters: Parameters: A suggestion.

[Dennis Monticelli]

Ken,

Ooops.  I forgot to list the osc drive voltage as part of the original data
set.

It was 132Vpp of which +17Vp was exhibited on the positive half cycle and
-115Vp on the negative half cycle.  According to the tube manual +17Vp at
500V plate with 250V on the screen will produce 360mAp from each tube.
 720mA peak vs 100mA average tells me the PA is definitely running class C
and helps explain the decent efficiency.  Of course with 100% plate mod
added this level of plate peak is truly necessary.

I will keep your grid resistor idea in mind the next time I crack open the
case.

BTW, the absolute biggest effect I have observed with respect to chirp was
not connected with the power supplies, it was a weak 1625.  One of the
tubes had sagged (after a year of heavy CW activity) from a gm of 3000 down
to below 2000, while the other tube held up at 3000+.  I replaced the weak
tube and the chirp disappeared (under regulated supply condition).

Dennis AE6C



On Mon, Mar 21, 2016 at 9:39 PM, Kenneth G. Gordon <kgordon2006 at frontier.com
> wrote:

> On 21 Mar 2016 at 20:30, Dennis Monticelli wrote:
>
> > Data from a T-22 measured in 2001.  All measurements key down.
> >
> > Vp = 468V
> > Ip = 106mA
> > Screen = 245V
> > Osc - 210V regulated via VR tubes
> > Grid bias = -52V across 16K (measured the R)
> > Grid current = 3.25mA
> > Coupling control at max
> > Pin = 49.5W
> > Pout = 27W  (54% efficiency)
>
> Perhaps if you reduced the grid resistor to about 12 K from 16 K your
> efficiency MIGHT
> improve slightly, although, as you say, 60% is pretty darned good.
>
> You might simply parallel the 16 K resistor you have there with a ~48 K
> resistor, which will
> give you 12 K. That way it would be easy to reverse.
>
> Doing that would reduce your grid voltage to ~ -45 VDC at 3.25 mA, which
> would be exactly
> the "book" value.
>
> On the other hand, "if it ain't broke, don't fix it". :-)
>
> Ken W7EKB
>
>
>
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