[Amps] MRF151G Vs VRF2933

[Roger (K8RI)]

Thanks for the input Jim.

I wonder how a passel of these 151Gs in PP / Parallel as in the Quadra 
would compare to the boards coming out of Israel?
The 151Gs, running the legal limit would be running near half their 
capacity. In a circuit "almost" identical to the Quadra they should 
produce a very clean signal at a good efficiency Near as I can tell, 
they need a 1 ohm resistor in series with each gate and possibly some 
tweaking with the transformers / combiners

For those not familiar with the quadra, it uses 8 MRF151s rated at 150W 
out.  The G "appears" to be a pair of 151s in a different package.

73, Roger (K8RI)


On 4/30/2017 12:04 AM, Jim Thomson wrote:
> Date: Sat, 29 Apr 2017 04:57:50 -0400
> From: "Roger (K8RI)" <k8ri at rogerhalstead.com>
> To: "amps at contesting.com" <amps at contesting.com>
> Subject: [Amps] MRF151G Vs VRF2933
>
>
> <Richardson shows the VRF2933 running into a short and an open, then back
> <to a 50 ohm load where a pair still put out 1200 watts at 65 volts. The
> <VRF2933 is rated for 300 W carrier at 50% efficiency. HOWEVER,  the
> signal is pulsed at 20% duty cycle. A pair running PP at 65 VDC put out
> 1200 watts. After shorting and going to an open circuit, they switched
> back to a 50 ohm load and was still putting out 1200 W. Actually a
> little more.
>
> They did not perform the same tests on the MRF 151G also rated at 300W
> RF but about $9.00 less.  The 300 W out with the 151G was not pulsed and
> again was at 50%
>
> Any thoughts?  Any better transistors?
>
>
> 73, Roger (K8RI)
>
> ##  Local buddy built the 2 x VRF-151G linear out of the arrl book.
> The VRF-151G is, I think the high voltage version of the MRF-151G.
> Runs good at 48-50 vdc.  IMD was excellent,  when run at  200-250 watts out.
> Took 7.5 watts  to drive it.   His K3 put out min IMD when run at 30 watts pep out.
> So a 6 db pad was used inside the hb amp.  The 30 w pep  from the K3  was reduced
> to 7.5 watts...which drove the hb  2 x  VFR-151G amp  to required levels.
>
> ##  another thought was to increase the NFB  by 6db, reducing the gain by 6db, then
> the 6db pad could be eliminated.  Then the imd would be further improved.
>
> Jim   VE7RF
>
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