Sounds like the power supply cannot deliver the current necessary. Could be excessive resistance somewhere along the line, or bad filter caps, or even the primary 120 VAC dropping . Start with the Primary AC and work your way through the power supply, measuring voltage drop under modulation. Don't overlook resistive ground connections. I will bet on the caps. Good luck.
73, Ed Richards K6UUZ On Wed, 13 Oct 2004 10:48:02 -0800 "Tom Elmore" <[EMAIL PROTECTED]> writes: > Yes there is a plate current position and it shows a definite rise in > current with modulation. There are dual 5U4's in the supply feeding > the > finals and modulator and I swapped them both out with the same > results. I am > leaning towards Gary suggestion that there is an impedance mismatch > causing > excessive current draw. Does anyone have a 5100B or know what the > impedance > of the primary and secondary should be. I will try another set of > caps this > evening when I get home there are 2 , 40uf in series on the B+ line. > ----- Original Message ----- > From: "Gary Schafer" <[EMAIL PROTECTED]> > To: "Discussion of AM Radio" <amradio@mailman.qth.net> > Sent: Wednesday, October 13, 2004 10:29 AM > Subject: Re: [AMRadio] B&W 5100B Modulation Update > > > > Tom, > > > > Try a new rectifier tube if you have one and see what you get. > > Easy way to check capacitors is to tack a new one in parallel with > the > > hv filter cap and see if you get any improvement. > > > > Does the 5100 have a meter position for modulator plate current? > If so > > what is it doing. > > If you have the wrong impedance taps on the mod transformer, the > > modulators may be drawing much more current than they should. Too > high > > an impedance tap into a low impedance final load will make the > > modulators draw very heavy current. > > > > 73 > > Gary K4FMX > > > > > > Tom Elmore wrote: > > > The caps are the first thing I should have checked and there is > a good > > > possibility they are dried up except I don't hear any hum in the > audio > when > > > monitoring on the receiver. Also I can make at least 125 watts > carrier > and > > > don't see much of a voltage drop on B+ when I run carrier only. > > > > > > -Tom > > > ----- Original Message ----- > > > From: "George Pritchard" <[EMAIL PROTECTED]> > > > To: "'Discussion of AM Radio'" <amradio@mailman.qth.net> > > > Sent: Wednesday, October 13, 2004 8:46 AM > > > Subject: RE: [AMRadio] B&W 5100B Modulation Update > > > > > > > > > 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: amradio@mailman.qth.net > > > 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:AMRadio@mailman.qth.net > > > > > > ______________________________________________________________ > > > AMRadio mailing list > > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > > Help: http://mailman.qth.net/mmfaq.html > > > Post: mailto:AMRadio@mailman.qth.net > > > > > > ______________________________________________________________ > > > AMRadio mailing list > > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > > Help: http://mailman.qth.net/mmfaq.html > > > Post: mailto:AMRadio@mailman.qth.net > > > > > > > > > > > ______________________________________________________________ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net >
