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Hey Kevin
Time to try a 2.25:1 stepdown on the phono stage. Could only find one example on the net on a 1671. Assuming it is the same wire hook up as a 1660.
He put b+ on 13 then connected 16/21 together with 18 to plate. He then put pos output on 2 and 9 and neg on 4 and 7 then tied 3/5 together and 8/10 together.
Is this the correct way to do this?
Thanks Tom
Follow Ups:
Do you want 4.5:2 or, with paralleled primaries for higher current, 2.25:1? If it's the latter as you have written, then see LL1660S/25mA 2.25:1 drawing attached.
Kevin Carter
K&K Audio
www.kandkaudio.com
Kevin
If I parallel the primaries does the current rating go to 50ma? And then the henries are less on the plate.
I have been using a 6dn7 at about 24 ma. Thinking about trying 46 and 45. Looks like 25 ma is ok for 46 but the 45 would like around 35ma. Their plate resistance is about 2000 ohms.
So for 6dn7 and 46 would you go series for more henries or parallel for current. Not sure if I could run a 45 at 25ma and what it would sound like.
As always thanks for the help
Tom
The current rating doubles and the inductance is reduced 4 fold.
If you want to use 40-45mA you would be better served by the parallel configuration, but the lowest frequency performance will be affected by the low inductance. Do you frequently play pipe organ music? If not, then perhaps it's not a big deal.
There is no problem running 35mA through the series connection, but you will lose a good deal of voltage swing. Operated at the rated current, the primary will swing 250Vrms at 30Hz (at 4.5:2 that would be 110Vrms output), but with a core "flux offset" of 10mA, these numbers would be reduced by 40%. If you don't need any more swing than that (and you no doubt don't with a phono preamp) then all would be well.
Kevin Carter
K&K Audio
www.kandkaudio.com
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