Yes I concur with this suggestion Steve.
With only 200 Volts on the screen in AB1 linear mode the 4CX1500B tubes are
likely being starved and held back like variously reported amongst 8410 amp
users. The screen voltage probably ought to be up around 275 to 300 Volts to
ensure unconstrained power output to 1500W+ without significant gain
compression.
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Steve Bookout
Sent: Monday, 5 November 2018 9:18 AM
To: amps@contesting.com
Subject: Re: [Amps] power limiting in 8410 amps?
Hello Jim,
I have several of them and it's all about the same.
Plus/minus on different bands, but quite similar.
I've had several people suggest it's because the screen voltage is only
200 volts.
73 de Steve, NR4M
On 11/3/2018 1:40 PM, Jim Thomson wrote:
> Date: Thu, 1 Nov 2018 19:32:58 -0400
> From: Steve Bookout <steve@nr4m.com>
> To: Amps@contesting.com
> Subject: [Amps] power limiting in 8410 amps?
>
> <I ask because, I have 4 of these amps in my M/M contest station and I've
> <always noticed that the higher the power out, the more input it takes to
> <get there.?? They tune up real nice and easy to about 1200 to 1300
> <watts, with about 40 watts of drive, but to get to 1500 seemed to be a
> <challenge.? Seemed like the gain would fall off, maybe taking twice as
> <much power to get the last 200 watts.
>
> <I know there is no real difference in the effect of
> <the power out, but I would rather get 1500 watts out @ 45 watts of
> <drive, than 65-70 watts of drive.
>
>
>
> <73 de Steve, NR4M
>
> ## whoa, if the 8410 requires just 40 watts for 1200-1300 w
> but 75-80 watts to get 1500w, something is amiss... as in the
> 8410 isnt linear under those conditions.. not even close. Are
> you sure whatever watt meter you are using to measure drive
> power is dead on..ditto with output wattmeter?
> The gain is falling off..and fast, when driven harder.
> Its almost like you have entered the gain compression region. A 2 tone
> imd test would show the effect right away.
>
> Your gain dropped from 14.95 db...down to 12.87 db. That's a 2.08 db drop.
>
> ## Does it do this on all bands ?
>
> Jim VE7RF
>
>
>
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