[Amps] Drifting Power

[Jim]

Replace the plate choke with an Ameritron/MFJ choke. RF parts also sells 
them, but they are quite a bit cheaper from Ameritron.

73

Jim W7RY


On 10/19/2021 11:26 AM, Victor Rosenthal wrote:
> The B&W 800 isn't suitable for 160m or for WARC bands.
>
> Victor 4X6GP
>
> On Tue, Oct 19, 2021, 16:23 Steve London <n2icarrl at gmail.com> wrote:
>
>> 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 at 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 at 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 at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps