To start this thread let me state that I am
on a SERIOUS budget when it comes to my radio hobby, so I'm always looking for ways that I can get top-shelf performance (or close to it) from inexpensive gear.
Right now I've got QRP capability on the HF
bands. I need an amplifier, but the FCC
type-accepted options are more expensive than I'd like. Because of this I've been looking at many different options, mostly broadband cb
I've found that RM Italy makes a decent amp for very little cash comparatively. Since the core push-pull transistor configuration is pretty much the same across almost all solid-state amps, the brand isn't overly important. What is important is the bandwidth. RM makes several simple amps that cover 80-10m, which was ultimately what sold me on the KL-300p and KL-400. I have examples of each, and I've upgraded the KL-300p to class AB as can be seen here.
The KL-400 is class AB from the factory.
Now that the amps are class AB, the only thing left is to provide a good mutli-band low-pass filter system. I decided that I would like to have a stand-alone low-pass filter box that I can put in line with ANY 100-150W amplifier I might own or build.. I don't plan on exceeding that power level until I can afford a legal-limit amp from a mainstream manufacturer.
I originally was going to build a set from scratch based on plans found in the ARRL book "RF Amplifier Classics", but then I found this sweet little kit: Kit - Low Pass Filter Module 100W Relay Control 160-10M
It's affordable and very easy to build thanks to extremely detailed instructions. Virgil (K5OOR) is very good with customer service and provded fast answers to the few questions I had.
Using a simple single-pole 6-position switch it is possible to switch between 6 bands, covering 160-10m. 12VDC must be supplied for the relays, but the current draw is negligible.
I've assembled and tested the circuit, it works great. Here are a couple pics of the completed PCB:
(I'll post pics of the entire completed box when I finish the build tonight or tomorrow)
Just thought I'd share this in case there are other ops out there that are interested in adding high-end features to basic CB
-type amps. These additional features (bias modification combined with band-specific low-pass filtering) provide a MUCH cleaner signal than class C CB
boxes on their own.. This is better for everyone involved. The station op gets a low-distortion signal on SSB
, and the rest of us get less splatter and interference on the bands.