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Title: Help needed spark problem Post by: iw5ci on February 15, 2010, 03:39:42 AM Hi, it's my first post in this forum , i am IW5CI from Florence.
Here in italy we have a nice AM net on 40 meters on saturday and sunday morning at 7190-7195. I am setting up a "real" AM transmitter a GELOSO 222 that uses 2 807' as modulators and a 6146 as RF final : this is the scheme: http://www.webalice.it/iw1pue/geloso/schema_g-22-tr.htm I have a problem, every time i put the radio in tx or i return in RX (by a rotary switch) i see sparks in the rotary switch and so i think i am slowly burning the contacts. I am shure there is some component fault that causes this problem, but i don't' know where to start troubleshooting. Can someone give me an hand? 73! Title: Re: Help needed spark problem Post by: w3jn on February 15, 2010, 04:40:11 AM It looks like as the switch is rotated from receive to transmit, a wiper grounds the screen supply of the 807 modulators thru a 33 ohm 1 watt resistor. That *cannot* be right.
The switch also switches the primary of the 807 plate supply transformer. That's probably where the sparks are coming from. You can reduce this by putting a .1 uf/1KV capacitor across those contacts. Title: Re: Help needed spark problem Post by: WA1GFZ on February 15, 2010, 12:58:18 PM Put a 100 ohm resistor in series with the cap so it acts like a snubber. The best fix so the switch lasts for ever is to add a relay with larger contacts to handle the switch functions. A 10 amp multiple pole relay would operate with the antenna transfer relay.
Title: Re: Help needed spark problem Post by: flintstone mop on February 15, 2010, 01:23:20 PM Welcome To AMFONE........IW5CI...........Nickname Andy? AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Glad that you joined us. I'm waiting for responses from Amateurs using A.M. in the Philippines. Welcome aboard Fred |