[Amps] Non-linear linear

[Paul Baldock]

Well ignore everything I said. It's a measurement error. I was 
assuming the input SWR was relatively constant with power levels and 
basing my input power variation on a voltage measurement on the scope 
sampling the input coax to the amp. Turns out the input SWR varies a 
lot with power input on all bands, for example on 20M 1.4 at 75W, 1.1 
at 35W, and 1.4 at 10W drive.

So now the new question, is such an input SWR variation typical of a 
GS35B?  My 2 x 3-500Z amp is almost constant with input drive (as is 
Jim's VE7RF)

- Paul




>-----Original Message-----
>From: Paul Baldock
>Sent: Thursday, January 30, 2014 4:42 PM
>To: amps at contesting.com ; jim.thom at telus.net
>Subject: Non-linear linear
>
>
>
>I have a problem with my home brew HF linear being non linear on one band.
>
>On 80, 40, 20, 12 and 10 with 75W drive my linear will give about
>1500W output. If I reduce the input power by 9.5dB the output goes
>down by 9.5dB. So all is good.
>
>On 15 with 75W drive my linear will give about 1500W output. If I
>reduce the input power by 9.5dB the output goes down by only 5.2dB. That's
>bad.
>
>On 17 with 75W drive my linear will give about 1500W output. If I
>reduce the input power by 9.5dB the output goes down by only 7.6dB.
>That's not too good but not as bad as 15.
>
>Some info on the amp:
>
>Single GS35B, about 3.7KV, Idle current 210mA. No parasitic choke.
>Ameritron plate choke.
>Shared PI output for 10 and 12. Shared PI output for15 and 17.
>Shared PI input coil for 10/12 and 15/17 but with padder caps
>switched in for the lower freq.
>
>One anomaly I notice is that at the lower power input on 15 the plate
>current is about 390mA, where as on 80/40/20/12/10 its about 300mA.
>
>At the high power input Plate Current is about 650mA on all bands and
>grid current is around 350mA. At the low power input grid current is
>zero on all bands.
>
>Any thoughts.
>
>- Paul   KW7Y
>
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