[Amps] Drifting Power

[Kim Elmore]

Do you see this when using a dummy load, or your antenna, or both?

Kim N5OP

"People that make music together cannot be enemies, at least as long as the music lasts." -- Paul Hindemith

> On Oct 16, 2021, at 11:23 AM, MU 4CX250B <4cx250b at miamioh.edu> wrote:
> 
> I’m not aware of any vacuum tube RF power amplifiers that are
> sensitive to room temperature changes. However, if fixed load
> capacitors heat up under full RF power, a frequent occurrence, that
> can affect the tuning. Ditto for marginal switch and relay contacts.
> In my experience, a falloff in power output, accompanied by a decrease
> in grid current, is also a frequent occurrence. This can be caused by
> external capacitor changes, or by weak tubes.
> 73,
> Jim w8zr
> 
> Sent from my iPhone
> 
>> On Oct 16, 2021, at 9:10 AM, Bruce Campbell <W8HW at comcast.net> wrote:
>> 
>> I have noticed that many amplifiers are designed to be most efficient _NOT_ at room temperatures, but a bit above room temp. A good compromise in design. I have noticed this is both tube and solid state amps. I do not have your amplifier in front of me, rather I am speaking in general.
>> 
>> 73, Bruce, W8HW
>> 
>> =========================================
>> 
>>>> On 10/16/2021 10:32 AM, Pete Smith N4ZR wrote:
>>> FWIW, I see something very similar in my KPA-1500.  I had assumed it was software protecting the transistors, just in case.
>>> 
>>> 73, Pete N4ZR
>>> Check out the new Reverse Beacon Network
>>> web server at<http://beta.reversebeacon.net>.
>>> For spots, please use your favorite
>>> "retail" DX cluster.
>>> 
>>>> On 10/16/2021 10:05 AM, Steve London 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
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