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Title: Need Noise Limiter ckt for BC-348-R Post by: K1CWS on January 11, 2010, 01:52:01 PM Anybody have a circuit for a simple series noise limiter for the BC-348? I have a ckt for a Q model I found in an old QST, but the original detector ckt in the Q model is different than my R model.
Title: Re: Need Noise Limiter ckt for BC-348-R Post by: WU2D on January 13, 2010, 07:16:54 AM Bruce,
The third edition of the CQ Surplus Radio Conversion Manual has a simple circuit using a 1N34 diode. I can scan the pages if you are interested - the file is too big for the whole manual. Also: The CQ Conversion Manual listed sources for 'Conversion Data': CQ MAGAZINE: September 1956 February 1959 March 1959 Mike WU2D Title: Re: Need Noise Limiter ckt for BC-348-R Post by: K1CWS on January 13, 2010, 09:23:27 AM Yes Mike, I would like to see that CQ circuit. Thanks.
Title: Re: Need Noise Limiter ckt for BC-348-R Post by: WD5JKO on January 13, 2010, 02:12:09 PM Bruce, I recall that Fair Radio used to sell a noise limiter add on for an old WW2 receiver. It was a little box that plugged into the octal socket for a 12H6, and it had two of the same types plugged into the top of the box. Then there was a front panel switch as part of the upgrade to turn on the noise limiter. Does anyone recall this? I think it was an add on to the TCS HF receiver. Jim WD5JKO Title: Re: Need Noise Limiter ckt for BC-348-R Post by: WB6NVH on January 14, 2010, 01:44:23 AM Quite so, TCS limiter kit. They must have made as many as they did receivers. Most of the limiter designs in that era were just the diode clipper style and in my experiece the switch should have been labeled "distortion on-off," but sometimes they helped.
Title: Re: Need Noise Limiter ckt for BC-348-R Post by: WU2D on January 14, 2010, 09:24:23 PM Here is the section in the Surplus Radio Conversion Manual Vol. III on adding a Noise silencer.
Mike Wu2D Title: Re: Need Noise Limiter ckt for BC-348-R Post by: WU2D on January 14, 2010, 09:38:55 PM Tube Lineup BC348R Belmont Radio: 3 ea 6K7, 6J7, 6C5, 6F7, 6B8, 6K6 and 991
Title: Re: Need Noise Limiter ckt for BC-348-R Post by: K1CWS on January 15, 2010, 10:08:34 AM Mike, the ckt u sent is for the BC-348-Q, I have attached ckts for both the R and Q model. How do I use the conversion ckt for the Q model in my R model?
Title: Re: Need Noise Limiter ckt for BC-348-R Post by: WU2D on January 15, 2010, 10:44:56 PM Bruce,
The R model actually has a nice detector and AGC system. It is hard to read the schematic but V193 Pin 5 is the detector diode and pin 4 is the separate AGC diode. The AGC cap appears to be 11-14 and I would highly recommend that you replace it because it probably is leaky and you need the AGC to work properly before tackling any limiter mod. Start by reading ER the September 2003 article Updating the Automatic Noise Limiter by Brian Breezley, K6STI. It is posted here: www.ham-radio.com/k6sti/anl.htm Mike WU2D Title: Re: Need Noise Limiter ckt for BC-348-R Post by: WU2D on January 15, 2010, 11:27:59 PM OK Bruce, AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
And guys check out the connections. But here are a couple of circuits to try - the first is a simple shunt self adjusting shunt noise limiter. This should work. The second is an attempt to employ the Updated automatic Noise Limiter. Use the article to adjust the circuit to the proper "OVERMODULATION" limit. 73's Mike |