Tom, It seems to me that the capacitor bank for the 600 volts is not working. Look at the B+ with a scope, and you may see the B+ drop at the audio rate. A "stiff" capacitor bank will show no audio waveform on the B+. If I'm right, the caps are died out. Is there any trace of Hum on the "dead carrier"? George AB2KC
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tom Elmore Sent: Wednesday, October 13, 2004 12:35 PM To: [email protected] Subject: [AMRadio] B&W 5100B Modulation Update Now that I have had some time to troubleshoot the B&W 5100B modulation here is what I found. The B+ is around 600 volts with no modulation and I as start to modulate and watch the scope when it reaches about 50% modulation the B+ drops from 600 to around 400 volts. I changed the final and modulator 6146 tubes and see the same results. The original modulation transformer has been replaced with a Chicago Standard Transformer Corporation # A-3891. When I remove B+ to the final's and terminate the modulation secondary into a resistive load of about 6k ohms I still see a significant drop in B+ as I start to bring modulation up. I don't have the original mod transformer and the manual I have doesn't say what the impedance should be. I have tried various other tap settings on the transformer secondary and don't see much of an improvement in reducing the amount of voltage drop. I wonder if it is possible that this mod transformer just will not work with this unit. Anyone have experience with mod transformers using 6146's as finals and modulators? Thank You Tom Elmore KA1NVZ Anchorage Alaska ______________________________________________________________ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected]
