[Amps] MRF151G Vs VRF2933

[Jim Thomson]

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