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A Dead Easy 50 mhz Preamp by VK3CJS

6M Preamp - Page 1

Here's a nice little kludge that works very well for me - I modified an old Realistic SSB CB radio for 6 metres. With a bigger PA it got out fine, with reports of good Tx audio. On receive though, it was deaf on account of it's simple grounded-base RF amplifier. I tried replacing the RF and mixer transistors with surface-mount types from old TV tuners and that livened things up a bit, but there was still an image problem because there was only one tuned circuit before the RF amp.

Internally, the old TRC-47 had been a bit of a brothel from the start and was now even worse on account of my mods..... what to do ??

The Realistic TRC-47 is an old fashioned 23 ch CB using 6 + 4 crystals and an 11 mhz IF filter.... just the thing for the experimenter. Here one crystal bank is replaced by a Super VXO with a sweep of 150 khz.... all ADDING to around 50.1 mhz. The PA stradding the back is a set of finals from a Philips FM-828 70 mhz carphone, here biased of Class AB. The stout finals are virtually immune to the abuses of the clumsiest fiddler. The coils in the PA are re-wound to bring them down to 50 mhz.
I might make that the topic of another article when time permits. :)

I decided to build an external RF amp with a bit of added selectivity. This meant bypassing the antenna relay in the old CB and bringing the Tx and Rx RF connections out via separate sockets. The T/R relay in the PA would do the switching for me.

But hell, I needed a preamp TODAY! The JA's were drifting in and out and you never know where the propagation might take you on a summer day.

I had a TV tuner on the bench. It had been extracted from a video recorder found on the tip. The very thing .... here's how I used it..........