FR6

From : WA9BVS @ WJ9U.IN.USA.NA #:1587
Subj : Ramsey FR-6 Mod

 
The Ramesey FR6 is a tunable 6 meter fm receiver.  It is available from Ramesy
in kit form.  When I built the kit I found that it had problems caused by
unstable voltage in the first (tunable) oscillator section.  The kitplans call
for 9 volts to be applied from a transistor device 9 volt battery to the LM386
audio output amp.  The 9 volts is dropped to about 6 volts by R20, a 270 ohm
resistor.  But the 9 volt battery is subject to varying current demand as the
audio being put out by the LM386 increases or decreases. This causes small
changes in the 9 volt voltage and small changes in the 6 volt voltage. The 6
volts is supposed to be steady and is used via R22 and the 5k tuning control
to operate the varactor D1 and tune the first oscillator.

I found that turning up the volume shifted the receive frequency as the
increased draw on the audio amp reduced all voltages on the rig slightly.
The afc appeared not to work properly.  I solved the problem by removing R20.
I then ran 12 volts + from a stable supply to the on/off switch instead of 9
volts from a battery. That put 12 volts on the LM386. It is rated for 12 volts
so it worked fine and produced more audio.  I then obtained a 317 3 pin
voltage regulator from Radio Shack and built the simple adjustable voltage
regulator shown in the Radio Amateur's Handbook.  Radio shack also has the
info on building the regulator circuit.  I used the 12 volts DC + from the
supply for the input and set the adjustable output to 6 volts.  The six volts
output from the regulator went to the junction of C35 (+) and R 21.

The receiver therefore has regulated 6 volts DC supplying it, except the
final audio amp which is connected direct to the 12 volt supply. The result
is that the receiver is as stable as can be expected from a tunable receiver
at 6 meters.  There is intermod from FM broadcast stations but the receiver is
quite usable with about a .6 micro-volt sensitive-quieting.

Good luck if you need a simple 6 meter fm tunable rcvr.

Malcolm WA9BVS @ WJ9U