The description of the "economy supply" circuit is accurate but I have found that some folks (me) have tried to lift with a switch or relay the connection of the bridge that would normally go to ground as method of standby. This will tend to make the center tap go negative. Placing a single diode in series with the center tap (low voltage output take off) before filter capacitors (anode to center tap) will eliminate this trouble.
John, WA5BXO -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Greg Sent: Wednesday, February 06, 2008 12:32 PM To: Discussion of AM Radio in the Amateur Service Subject: Re: [AMRadio] Re: WTB: HV Tranny OK JT So I was right? Wow! Finding the replacement transformer will be difficult for the Multi Elmac due to the tapped secondary and current requirement. An "Economy" supply puts out two voltages: high voltage and half the high voltage using only one winding of a center tapped transformer. You build it like the classic full wave bridge with two diodes and a filter. Then you unground the center tap and use the center tap as the half voltage and then filter and bleed it. The schematic is on the internet and the radio handbooks and is well accepted by everyone. If you are shooting for 500 vdc on the 6146 plate what I suggest is find a 400 vac 200 ma or so transformer as the main power source. The pi net filter will boost the dc output to the 500 volt range then do the 1/2 voltage trick with another pi net filter and bleeder. The Multi Elmac is tolerant to a degree of over/ under voltage but I would not recommend taking the 6146 to 600 vdc or above. What I did here is took a Hallicrafters transverter power supply and modified it. Used a large dropping resistor with sliding tap to drop the 750 vdc to 500 vdc and added a soild state relay and 12 vdc power supply to key the HV transformer thru the hand mic. This avoids keying the radio with no load and the full 750 vdc appearing in the Multi Elmac. The filaments are lit thru a separate transformer that is not keyed. It works ok and with 500 vdc on the rig I get 25-30 w of AM out on 75m. The audio is ok but not spectacular. VFO is stable. I think the bottom line on your transformer quest is that you won't be able to find the exact right transformer any time soon and will have to do engineering/ adaption to get you to where you need to go. I am stocked out of any transformers that can be adapted to your rig. Some where there's a Elmac net that meets on 75m am. You wouldn't have a reference for that would you? 73's Greg WA7LYO Kinston NC ----- Original Message ----- From: "JT Croteau" <[EMAIL PROTECTED]> To: "Discussion of AM Radio in the Amateur Service" <[email protected]> Sent: Wednesday, February 06, 2008 12:42 PM Subject: Re: [AMRadio] Re: WTB: HV Tranny > On Feb 6, 2008 12:31 PM, Greg <[EMAIL PROTECTED]> wrote: >> Is this for an AF 67? I just built up a supply for my AF 67 and that's >> pretty much what the circuit calls for. > > It sure is. > >> Do you need a tapped secondary for the dual HV or can you do it via the >> "Economy Supply" method of lifting the secondary CT ground and taking 1/2 >> total voltage for the low B plus supply? To do that you will need a 400 >> vac ct >> transformer at 225 ma. and a full wave bridge rectifier. > > I was going to just build it per the PS-2V schematic, I'm not familiar > with this "economy" method. > > Thanks > > -- > JT Croteau, N1ESE - Manchester, NH (FN42gx) > ______________________________________________________________ > Our Main Website: http://www.amfone.net > AMRadio mailing list > List Rules (must read!): http://w5ami.net/amradiofaq.html > List Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > To unsubscribe, send an email to [EMAIL PROTECTED] with > the word unsubscribe in the message body. ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected] To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body. ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected] To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
