Brett, I just get nervous about "overextending" my 32V transmitters. I have 4 at the Collins Radio Center and no spare transformers in the event one of them breaks down. So you can see why I am hesitant about switching the toggle on the rear to 700 volts.
Take care and continue to experiment/homebrew. Great to see someone is doing what others only talk about!! Dave, W3ST Secretary to the Collins Radio Association Publisher of the Collins Journal www.collinsra.com ----- Original Message ----- From: "Brett Gazdzinski" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Saturday, January 24, 2004 10:39 PM Subject: RE: [AMRadio] 4D32 rig testing > Don, > I was in qso with Jay, n2wwl today, and we were talking about > the 32v3, and the voltage it runs at, Jay runs his on the low voltage > position, > about 600 volts on the plates. > I run mine on the 700 volt tap, 180 to 200 ma. > > The panel meter says 800 volts high voltage, but I put my > DMM on it and was very surprised to find 940 volts on the plates. > > I have been running them that way for 15 years with the same tubes > in them, and used to use them quite a lot. > > I get 100 watts out, and 350 watts pep. > I have solid stated the power supplies, which explains the high > voltage. > > I think, as long as you don't exceed the plate dissipation, > you are likely ok with most tubes. > > Brett > N2DTS > > > > > > > > > >Collins runs them at over 700 volts in class C plate > > >modulated service (32V series). > > >If they don't arc over, and you don't exceed the plate dissipation, > > >what would be the problem? > > > > > > > That's a good point. I recall an article pre-WW2 in QST > > which described > > getting high peak audio power from modulator tubes by running > > unusually high > > voltage on them, but staying within the rated dissipation > > rating. A point > > was made that for example, the 807 is rated for a maximum of > > 600 volts plate > > modulated. That means the peak voltage would be at least > > 1200 volts, and > > that doesn't hurt them, and is still within factory specified > > ratings. So > > for intermittent service, you should be able to run as much > > as 1200 DC volts > > on an 807. I think the limit on plate modulated voltage > > would be the point > > where arcovers would begin. > > > > However, I do recall using a quad of p-p parallel 2A3's in my > > audio driver. > > I didn't have a proper driver transformer at the time, so I > > ran them @ 400 > > volts/30 m.a. each tube. They are rated at 300 volts/40 m.a. > > maximum in the > > RCA manual. That way I could get plenty of peak driving > > voltage to the > > class B grids, despite having a driver transformer with too > > much stepdown, > > but with exactly the same plate dissipation as per RCA > > recommended ratings. > > They worked great, and drove the modulator tubes with very little > > distortion. But I noticed that within a few months, the > > 2A3's would get > > weak. I went through a couple of sets that way. Finally, I > > obtained a > > proper driver transformer with the proper turns ratio, and > > slowered the > > plate voltage back to 300v, and changed the bias so that each > > tube would > > draw 40 m.a., and now I have had the same set of 2A3's for > > almost 10 years, > > and they still test good. Maybe just a coincidence, but at > > the current > > price of a new 2A3, I don't feel like trying to find out. > > > > My conclusion is that some tubes may not take overvoltage > > very well, while > > others will not be harmed, and the only way to find out which > > ones is to try > > them and see. If your tubes seem to be short lived, go back to the > > recommended parameters. > > > > -K4KYV > > > > _________________________________________________________________ > > High-speed usersbe more efficient online with the new MSN > > Premium Internet > > Software. http://join.msn.com/?pgmarket=en-us&page=byoa/prem&ST=1 > > > > _______________________________________________ > > AMRadio mailing list > > [email protected] > > http://mailman.qth.net/mailman/listinfo/amradio > > > > _______________________________________________ > AMRadio mailing list > [email protected] > http://mailman.qth.net/mailman/listinfo/amradio
