Plate to plate impedance on the 6L6's is going to be in the neighborhood of 5000 to 6000 ohms. 400 volts plate to plate voltage swing would be around 26 watts of audio.
Plate voltage swing to ground would be 1/2 the above or around 200 volts to ground for 1 tube. Since there is about 26 volts of bias on the grids the peak grid voltage at greater than 26 volts will cause grid current to start to flow and the tubes will be slightly into AB2 operation, which I think they do get into. I believe you measured around 20 volts on the grid to ground so it is in the ball park. But the plate voltage swing seems awfully low. It is difficult to detect a shorted modulation transformer sometimes. As Larry says it is hard to detect shorted turns by measuring with an ohmmeter. I once had a mod transformer that looked ok at low signal levels and resistance measurements looked fine. But when a small amount of audio power was applied it would break down and short. Look at the grids again when applying audio and see if the peak voltage reaches the bias voltage. Also put the scope on the center tap of the driver transformer and DC couple it and see if you see any movement when applying audio. That will be an indication of grid current being drawn. Then if you still have only 50 volts on the plates of the mod tubes-- something is amiss. 73 Gary K4FMX > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:amradio- > [EMAIL PROTECTED] On Behalf Of Jack Schmidling > Sent: Friday, November 17, 2006 5:50 PM > To: Discussion of AM Radio in the Amateur Service > Subject: Re: [AMRadio] Ranger Audio... the numbers > > Larry Taft wrote: > > > Just from "rule of thumb" for audio tube amps you should get a couple > > hundred volts audio swing (not related to BIRD WATTS) at each plate to > > ground. 50 v is only a couple of watts audio. > > Could you explain the math on that? How do you arrive at watts knowing > only volts? > > As a data point, 50v into a 50 ohm load is 50Watts > > > js > > -- > PHOTO OF THE WEEK: http://schmidling.com/pow.htm > Astronomy, Beer, Cheese, Fiber,Gems, Sausage,Silver http://schmidling.com > > ______________________________________________________________ > AMRadio mailing list > List Home: http://mailman.qth.net/mailman/listinfo/amradio > Partner Website: http://www.amfone.net > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] ______________________________________________________________ AMRadio mailing list List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected]
