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<DIV><FONT size=2>I have found a bias mod that works very well with push-pull
6BQ5 tubes..</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>Remove cathode bias resistor(s) to ground and
cap(s)</FONT></DIV>
<DIV><FONT size=2> Add 50UF 25WVDC from each EL84(6BQ5) to
ground.</FONT></DIV>
<DIV><FONT size=2>USE 2 7805 Vreg IC TO220 3 term. 5V neg Vreg IC.one for each
EL84(6BQ5)</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>connect Vin of reg ic. to cathode.</FONT></DIV>
<DIV><FONT size=2>connect ground to ground.</FONT></DIV>
<DIV><FONT size=2>connect V out to 150ohm 1/2 watt resistor to
ground.</FONT></DIV>
<DIV><FONT size=2>Do this for each EL84(6BQ5)</FONT></DIV>
<DIV><FONT size=2>This will give APPX 12V from cathode to ground.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>This mod will make more stable cathode bias and will auto adj
cathode voltage to meet </FONT></DIV>
<DIV><FONT size=2>tube bias current.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>This is good for tube life as they go un-bal threw the
life.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>I did this mod on a heathkit EA-2 and workd very
well.</FONT></DIV>
<DIV><FONT size=2> you can also use SV83 tubes from SVETIANA..</FONT></DIV>
<DIV><FONT size=2>go to <A href="http://www.svetlana.com">www.svetlana.com</A>
and go to techinical bulletin No 29.</FONT></DIV>
<DIV><FONT size=2>I did not try the bias mod on SV 83 tubes.</FONT></DIV>
<DIV><FONT size=2>SV 83 tubes have slightly different bias req.</FONT></DIV>
<DIV><FONT size=2>drop resistor (cathode to ground) buy appx 20%</FONT></DIV>
<DIV><FONT size=2>see tube spec for bias current.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>This bias mod should work on most output tubes.</FONT></DIV>
<DIV><FONT size=2>set resistor for bias current.</FONT></DIV>
<DIV><FONT size=2>I did not try it yet on 6L6GC tubes yet.</FONT></DIV>
<DIV><FONT size=2>bias mod is ok for 6V6 tubes.fine tune resistor.</FONT></DIV>
<DIV><FONT size=2>you could use a 317T reg with a smaller resistor to ground and
a small pot on ADJ lead.</FONT></DIV>
<DIV><FONT size=2>to have ADJ bias.I did not try this yet but will
work.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>Bob </FONT></DIV>
<DIV><FONT size=2><A
href="mailto:Rascal@Utec.net">Rascal@Utec.net</A></FONT></DIV>
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