I have an older solid state amp based on a pair of MRF 454s. The amp is
missing three common design features found in most similar HF power
amps, a bias circuit for the base, negative feedback, and a phasing
transformer on the DC input.
1. What is the normal bias set for this type of amp. Setting bias to the
current turn on point about .62 V results in a clean signal between
about 14 MHz and 30 MHz.
2. Is it practical to copy the RC values from a similar amp to implement
a feedback circuit?
3. The imput signal seems to be affected by feedback from the amp. Below
10 MHz there is a second order harmonic on the input signal. I am not
sure of the cause of this. At low frequency the output looks clipped. It
looks as though it is being over driven.
4. The board appears to have two grounds, a DC ground and an RF ground.
What is the purpose of this design approach? The APP note circuits do
not have this. Is it as simple as connecting the two grounds together?
Is there a downside to trying this?
Thanks for your analysis. Dan kb0qil
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