Thanks to all for the many useful comments.
To answer a few questions:
1) The input and output SWR remain constant while the power output is
drifting. Using ArraySolutions PowerMaster wattmeters to verify this.
2) The input drive power is 29 watts, and remains constant as the output
power drifts.
3) The RF choke does get quite warm. However, it shows no sign of heat
damage to the coil form, tape or wire. The only interesting thing about the
choke is there is a small recessed "dimple" in the plastic form. Maybe a
manufacturing defect ?
4) No other tank circuit components are heating up. The tank circuit looks
pristine.
I do have a B&W 800 RF choke in the junk box, but does it have enough L for
160 meters ? Where are the series resonances ? Maybe I could try it on 15
meters to see if the original RF choke is the cause of the drift ?
73,
Steve, N2IC
On Sun, Oct 17, 2021 at 4:36 AM AJ <iamfromcanadaalso@gmail.com> wrote:
> Hi Steve
>
> Few things.
>
> What is the input vswr doing when this happens?
> What drive power are you using?
> What is the grid and plate current doing when this happens?
> The relay, caps or inductor in the circuit could be a issue.
> As Kim asked is this into a dummy load or antenna or a antenna tuner?
>
> The thing is what you are saying is a most likely an issue with the
> plate choke but you say it only happens on 15 meters which is strange as
> that should be on 10 and 20 also on that amp.
>
> Have you had the cover off and looked at the plate choke?
>
>
> Cheers AJ___ VE3HJ
>
>
> On Sat, 16 Oct 2021 08:05:14 -0600
> Steve London <n2icarrl@gmail.com> wrote:
>
> > I have a Commander HF-2500 Magnum, with a pair of 3CPX800's. Great
> > amp.
> >
> > It has one quirk, and only on 15 meters. If the amp has been dormant
> > for a while, the output power is initially low: about 1100 watts. Key
> > down it gradually rises up to 1500 watts over about 10 seconds. After
> > that, if I intermittently transmit, at least every 5 minutes, it will
> > stay at 1500 watts. Only after being idle for ~30 minutes will it go
> > back to the low output state.
> >
> > My thought is that something in the input pi network is heating up.
> > However, I have accurate SWR/power meters on both the amp input and
> > amp output. Neither the input power nor SWR is changing as the output
> > power rises. As the power rises, the grid current drops, but the
> > plate current is unchanged. Again, this is only on 15 meters.
> >
> > Suggestions ?
> > 73,
> > Steve, N2IC
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|