Jim -- As was pointed out earlier, it depends. On radios like the 5100B, HT-32, HT-37, DX-100 etc, tubes such as the 5R4, 5V4 etc can add up to a fair percentage of the current budget. Filament winding shorts are well known on the Hallicrafters and Heathkit transmitters. Replacing the rectifiers goes a long way to saving the transformers and a potentially expensive transformer rewind.
Check to see what's down-stream of the rectifiers. Typically, the parts down stream of the HV rectifiers can stand the higher voltage, but spending 30 minutes to check could save a few hours in repair work. 73 Mark K3ZX ----- Original Message ----- From: "Jim candela" <[EMAIL PROTECTED]> To: "[email protected]" <[email protected]> Sent: Thursday, March 18, 2004 10:45 AM Subject: [AMRadio] Solid State Plug in Tube Rectifier Replacements, "are these OK to use ?" > > 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 >
