Sequel to "How many Hammond 155J chokes?"

[tpatton]

I'll name the Seduction's three PS 220 uF caps by their terminals: Outer is 20, 25, Middle is 14, 15, and Inner is 11, 12.  After adding my 2nd 155J choke, to 15, 25 after a first to 12, 15 (replacing a pair of 1K ohms resistors), I had both halves of a Mundorf M-Lytic 100 + 100 as Inner, a 200 uF JJ as Middle, and Outer left stock (a Panasonic?).  Following Causasion Blackplate's suggestion that less uF would work, I removed the JJ and used, for Inner and Middle, the two halves of the Mundorf M-Lytic 100 + 100.  This left room for more bypass film caps as recommended by Grainger: two Obbligato film/oil 2.0 uF's for Inner and Middle, instead of just one for Inner. The sum of these changes was the biggest single improvement I've ever made in a phono or power amp: the gain in sharp, clear fine detail, in particular, was striking.  I have to wonder if the smaller capacitance is not just allowable, given the second choke, but positively better than the original 220 uF size.  In any case, I'm most grateful to CB for suggesting this change, which I'd strongly recommend to other Seduction owners--but be sure to use Grainger's idea as well, to put the final icing on this cake.

[Caucasian Blackplate]

No prob, I'm glad you like the changes! 

[2wo]

Hmm, I will have to try a shunt reg sometime, yea I know it means a new transformer...But still...John

[Caucasian Blackplate]

Hmm, I will have to try a shunt reg sometime, yea I know it means a new transformer...But still...John

You might just barely be able to eek out enough current from the PT-1 to shunt regulate a Seduction with a gas tube.  PJ is really the only person who would know.  It would be C4S current for each tube, plus 4ma of LED bias current, plus at least 5ma for the gas tube.  If all of that was less than or equal to the available PT-1 current, you'd be OK (you would probably want to use a full wave bridge rectifier off the PT-1 to do this).

[Paul Joppa]

I'll have to work up some numbers more carefully, but what PB proposes might be possible based on a preliminary look. Good one!

You'd do a fullwave bridge with the whole secondary, and must use a choke-input filter - probably a larger choke than the 155J, I'll have to look at it carefully. One choke might be enough, since there's a regulator to follow. Certainly no more than two chokes. I pretty much guarantee it would sound better. Hard to see where the new gas-reg tube would go though?

Off and on we've talked of a Seduction II, on the larger 8 by 10 chassis and with some modest layout, circuit, and buildability improvements. It never was much different sonically, just these small improvements and switching to the new C4S boards for inventory reasons. But if we could get a shunt reg in too, it might make some sense after all.

[Caucasian Blackplate]

Perhaps going to one bias string for the C4S boards would free up just enough?  The FWB with choke input is a very good idea, isn't there a 7 or 9 pin 150v regulator?

[Paul Joppa]

Perhaps going to one bias string for the C4S boards would free up just enough?  The FWB with choke input is a very good idea, isn't there a 7 or 9 pin 150v regulator?

Yes - 0A2, 7-pin. Max current is only 30mA, but the regulation spec is better than the 0D3. 0B2 at 105v is another possibility, if you have the C4S plate loads.

The dual bias strings on the Seduction C4S prevent a set of multiple wild voltage swings on start-up. Another lesson learned the hard way!

I took another look, and it looks pretty good. I think we can draw 30mADC from a fullwave bridge into an LC filter with 30 henries. That just happens to be the SEX amp plate choke value, and anyone who has upgraded a SEX amp probably has a couple of those lying idle.