Date: Sat, 29 Apr 2017 04:57:50 -0400
From: "Roger (K8RI)" <k8ri@rogerhalstead.com>
To: "amps@contesting.com" <amps@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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