Clansman PRC320 unstable. - UK Vintage Radio Repair and Restoration Discussion Forum

REILLY PATRICK · 7th Nov 2018, 6:37 pm

Hello.

I am new to this forum. I just got 2 weeks ago a PRC320 for the one i already install the LSB kit which fonction correctly but i discovered a problem the rig is already instable in frequency, does the lsb kit must be shielded or the problem coming from the slave oscilator or maybe the synthetiser ?
any suggestions will be appriciated.

my best regards

Reilly Patrick
F6FCM

PS: test has been made with regulated 28v power supply
same symptom with battery

G6Tanuki · 7th Nov 2018, 7:38 pm

There are 2 common causes of instability [frequency-scintillation] of the PRC320.

One: the contacts on the rotating band-selector can become tarnished. Rotate the band-selector knob clockwise through several complete rotations and it can help remove the tarnish.

Two: There are several tantalum capacitiors in "module 5" the power-supply. These are rated at 130V and are operated at 125V. They become leaky and cause the +120V synthesizer/VCO control-voltage to wobble slightly. Replace them with modern 160V electrolytics.

See here: http://www.vmarsmanuals.co.uk/newsle.../prc320psu.pdf

M3VUV51 · 8th Nov 2018, 4:31 am

theres also tants in the synth go leaky,and you dont need to shield the lsb carrier insertion oscillator.

M3VUV51 · 8th Nov 2018, 4:34 am

its a small world the article you linked in vmars was written by a personal friend of mine colin g4ddi,theres not a lot he doesent know about all things clansman.

ex seismic · 8th Nov 2018, 9:34 am

Rotate the band-selector knob clockwise..........

And only turn it clockwise if you want to preserve the contacts in it.

gmb

7th Nov 2018, 6:37 pm	#1
REILLY PATRICK Retired Dormant Member Join Date: Nov 2018 Location: Paris, France Posts: 1	Clansman PRC320 unstable. Hello. I am new to this forum. I just got 2 weeks ago a PRC320 for the one i already install the LSB kit which fonction correctly but i discovered a problem the rig is already instable in frequency, does the lsb kit must be shielded or the problem coming from the slave oscilator or maybe the synthetiser ? any suggestions will be appriciated. my best regards Reilly Patrick F6FCM PS: test has been made with regulated 28v power supply same symptom with battery

7th Nov 2018, 7:38 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	Re: Clansman PRC320 unstable. There are 2 common causes of instability [frequency-scintillation] of the PRC320. One: the contacts on the rotating band-selector can become tarnished. Rotate the band-selector knob clockwise through several complete rotations and it can help remove the tarnish. Two: There are several tantalum capacitiors in "module 5" the power-supply. These are rated at 130V and are operated at 125V. They become leaky and cause the +120V synthesizer/VCO control-voltage to wobble slightly. Replace them with modern 160V electrolytics. See here: http://www.vmarsmanuals.co.uk/newsle.../prc320psu.pdf

8th Nov 2018, 4:31 am	#3
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: Clansman PRC320 unstable. theres also tants in the synth go leaky,and you dont need to shield the lsb carrier insertion oscillator.

8th Nov 2018, 4:34 am	#4
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: Clansman PRC320 unstable. its a small world the article you linked in vmars was written by a personal friend of mine colin g4ddi,theres not a lot he doesent know about all things clansman.

8th Nov 2018, 9:34 am	#5
ex seismic Heptode Join Date: Sep 2009 Location: Tonbridge, Kent, UK. Posts: 686	Re: Clansman PRC320 unstable. Rotate the band-selector knob clockwise.......... And only turn it clockwise if you want to preserve the contacts in it. gmb