Bob KD7YZ wrote:
> Roger said the following, On 4/27/2010 2:20 PM:
>
>
>> You apparently have something heating but it may not be in the amp.
>>
>
> can be .. I know that the top of the case over the tubes gets a little
> feisty when I am trying to run legal limit on FSK ...it's alright with
> SSB and CW at these levels.
>
First, the Palstar (They purchased Command Technologies) 2000 6-meter
amp is rated at 1500 PEP, 1200 RTTY and digital and they say they have
redesigned the amps to make them more rugged, so you are running it a
bit hard at 1400 on digital. I don't have information on the Command
2000, but I do for it's Palstar replacement.
http://www.palstar.com/vhf_2000.php I'd expect the output air for a
pair of 3CPX800s running the legal limit on digital to get pretty toasty .
Every amp I've had with the exception of the Alpha 76A and Dentron
MLA2500 got hot over the tubes. Even the 76A does on long
transmissions. The Henry 2K4 got really hot. The air coming out of the
present one running an FU728F (Tetrode) gets uncomfortably warm with
high duty cycle operation. But it's rated for key down at 1500 watts.
> I ran it thru the paces before trying sustained operating. I wrote don a
> chart of tuning settings and readings. These stay true to form and are
> repeatable when I tune up. It's when I run FSK or KT65 for several one
> minute sequences that the case gets warm and the power falls off.
>
> I'll check the 240 plug fwiw to see if it's too hot.
>
> The input is steady from the FT-950. The SWR on the output side of Amp
> is nearly 1.1:1 and reds that way throughout. If I just stay at 1000 on
> FSK (for example) I see no degradation. Though I haven't tried that for
> say 45 minutes.
>
>
Does the plate voltage and current stay the same as when you first
transmit or does either fall off when the power falls off. If the SWR
isn't changing I'd not expect the problem to be in the antenna or feed
line.
> So you guys are saying that you already run JT65a sequences for much
> longer than I do and you see no issues?
>
> me bad then cuz I'm clearly causing it here.
>
>
>
>
73
Roger (K8RI)
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