Funny, I have solid stated everything, past and present, loads of receivers and transmitters, without doing anything but replacing the tube rectifiers with solid state diodes, and never had a tube failure or other problem.
Even running the 32V3 transmitters on the 700 volt tap with solid state rectifiers, both have run for years and years with the original tubes they had in them when I bought them 20 years ago. I also used to use them as exciters, so had a variac in the plate supply, and found the rigs running 940 volts on the plates, with no problems! Some receivers I never bothered with solid stating, others I did, no problems. You should adjust the modulator bias, but otherwise, an extra 100 volts or so only seems to make things work better in transmitters. If you are running something so close to crap out that a bit extra voltage will push it over the edge, that gear needs attention! In running various boat anchors and home brew rigs for years and years, the ONLY tube crap out I ever had was a 75TH in the Collins 30K-1. Filament opened up... I have not gone through a single other tube, despite the fact most of my tubes are used hamfest specials, including the little ones. I think I do have some weak 6146 tubes that were in used gear, or hamfest specials, but don't use 6146 tubes in anything. I also had some broadcast pullouts, 4-250, 4-400 tubes that had weak output, but they worked. The only other problem was a bunch of very used 4cx250b tubes that tend to arc over inside as the cathode stuff coats the inside of the tube. So I don't loose any sleep over filament voltage, b+ on before the tube warms up, etc. Just my two cents... Brett N2DTS > > > A friend recently asked me the question, "are these OK to use ?" > > > http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3084286355&; > category=4674 > > > My long winded answer: > > > No simple answer here. There is a school of thought that > says tubes with > indirectly heated cathodes need to be at temperature before the plate > voltage is applied. That said a 5U4, 5Y3, or 5R4 will heat > up, and supply B+ > before the indirectly heated tubes warm up. Tektronix used solid state > rectifiers in their old tube oscilloscopes, but they also > used a time delay > relay (abt. 30 seconds). The other issue here is the directly > heated vacuum > tube rectifiers had a fairly high series impedance, and the forward > conducting diodes would drop a fair amount of voltage. In a > capacitor input > filter, this would lower the output B+ considerably from the > peak value of > the AC out of the HV secondary. If you stick in these solid > state diodes, > the B+ will be immediate, and likely 20-30% higher than > before. This leaves > a few options: > > a.. Switch the filter to choke input, and double up the > output capacitor > size. The B+ may be a little lower than before, but > considering the higher > AC line voltage these days, the B+ may come out just as the > boat anchor > designer intended. To get the AC ripple down to where it was > before, you may > need to increase the output capacitor to ~ 4X what it was before. *** > b.. Do the above, but add a time delay relay. Put N.O. > switch contacts > from HV secondary CT to ground. **** > c.. Stay with a Pi filter, but put a vacuum tube diode in > series with the > rectified B+ between the SS diodes, and the filter. A couple > of options are > the 6W4, and GZ-34. For the GZ, parallel the two sections. > These are low > drop indirectly heated diodes with a long warm up time (> 15 > seconds). I > like the 6W4 (dirt cheap TV damper diode) idea ran off the 5 > Vac filament > winding (longer warm up time). If the B+ is still a little high, add a > little resistance in series with the tube diode (in 50 ohm > increments). **** > d.. Just switch the rectifier to a GZ-34, and add > resistance to drop the > B+ to where it was before. Don't overload the GZ-34. This is best in > circuits that used 5Y3's. Russian GZ's cost about $12.00 > each, and work > really well. ***** > e.. Leave well enough alone! ******************* > Or would you rather I said, "sure, those would work great"! > > I didn't get into the SS diode reverse recovery issue (like what the > Hex-Fred's try to address), PIV limiting (varistor across > xfmr primary, R-C > snubbers, etc.). > > -:) > > > --- StripMime Report -- processed MIME parts --- > multipart/alternative > text/plain (text body -- kept) > text/html > The reason this message is shown is because the post was in HTML > or had an attachment. Attachments are not allowed. To learn how > to post in Plain-Text go to: http://www.expita.com/nomime.html --- > _______________________________________________ > AMRadio mailing list > [email protected] > http://mailman.qth.net/mailman/listinfo/amradio
