Dave, many people run them on low voltage, that is ok with me. I have been running mine on the high voltage for 15 years with no crap outs at all, not a single problem with them.
The low voltage transformer frequently went because it was overloaded, and removing the vacuum rectifiers reduces the load a lot. peter Dahl sells replacements, they are likely not cheap, but are good transformers. The only mod transformer I ever blew out was in the 30K1 I had, testing it with 20hz at 100% modulation at full power. Stupid, but I did not know anything then, and the 30K1 cost me less than the peter Dahl 32v3 mod transformer ($200.00). Serial number 9, I wonder if its on the air now, it used to sound very good when I sold it to someone down south. Brett N2DTS > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of David Knepper > Sent: Saturday, January 24, 2004 4:10 PM > To: [email protected] > Subject: Re: [AMRadio] 4D32 rig testing > > > Please excuse my ignorance among the experts but shouldn't > one be careful > not to push the voltage rating on the secondary of the modulation > transformer when increasing the plate voltage on the RF > amplifier? or on the > primary winding when pushing higher voltage on the mod. tubes. > > On all of my 32V's at the Collins Radio Center, I put the > toggle switch on > the rear to 600 volts, not 700 volts. Know where I can get a > replacement > mod. transformer for the 32V transmitter? I don't! > > Inquiring minds would like to know! Why sacrifice a > modulation transformer, > which are expensive and rare these days. > > Thank you > Dave, W3ST > Secretary to the Collins Radio Association > Publisher of the Collins Journal > www.collinsra.com > ----- Original Message ----- > From: "Donald Chester" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Saturday, January 24, 2004 3:47 PM > Subject: RE: [AMRadio] 4D32 rig testing > > > > > > > > >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 users-be 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
