Hi everyone, I'm looking for recommendations for a high-current (>4A), low output (<50 Ohms; but preferably as close to 0 Ohms as possible) impedance amplifier working from 30MHz to, roughly, 1MHz (the lower the better). I thought someone might have been exposed to such a commercial amplifier, or could tell me how to modify an otherwise available amp (rip out the matching transformer network, for example).

My mostly-capacitive load is 1 Ohm to 0.001 Ohm range, depending on frequency (10KHz to 30MHz), and I'd like to get 10mVpp across it at any particular frequency. Need a sinewave or any other waveform containing a strong fundamental frequency (can live with ugly harmonics, just need strong fundamental present to view on spectrum analyzer; sinewave is ideal of course).

My online searching has found some close-misses:

1. Exactly what I need for below ~1MHz (output impedance 0 Ohms, can drive short circuit without harming itself), but looking for something else for above 1MHz:
http://www.rf-pwr-amps.com/Product Imformation.html

2. This one is great, it can drive a short circuit without harming itself, but high (50 Ohms) output impedance limits current to ~4A in this price range ($14K USD), and higher current units are much more expensive:
http://www.amplifiers.com/html/18200.asp?id=9

3. This one has 1 Ohm output impedance, but current is limited to 2A, and bandwidth is only 5MHz.
http://flcelectronics.com/f30pv.html

Any recommendations for what can be done is much appreciated. Also, does anyone have experience with cables that can carry high current (10App, ~200mVpp max) to the load? Distance can be made short (< two feet or even less) to avoid transmission-line effects of 50 Ohm cables (can ignore T-line if distance < one-tenth of wavelength, I assume).

Thanks in advance

 

Can you say what the application is? It's not too surprising that you keep finding amps with output impedances @ 50 ohms - most stuff in the RF range uses that for efficient energy transfer.

 

Have a look at high-power, high-frequency buffers opamps.

Examples are
Intersil EL1517 (up to 450mA at up to 200MHz)
or
Linear Technology LT1210 (up to 1.1A at up to 35MHz).

These are just the first two I found, there are many others.