nickel in PS chokes, plate chokes, and output trannies?
Posted: Sun Feb 27, 2005 9:23 pm
Hi Dave and all,
Finally got around to it: Here are the present and proposed preamp schematics that pertain to magnetic upgrades.
All in all, the pre is working but with a few problems. Firstly, upon replacing out the last 380 uF electrolytic cap in the HT PS with a 100uF oiler, ripple rose from 0 to 12mV and it is clearly audible, as it gets in the way of the phono stage. That should get cleared up by the HT PS change shown, ie. putting a new nickel(?) choke between the 100 mike and 30 mike caps. While we're at it, might as well change the 80 rectifier to 5ar4, bringing up the voltage, which slightly reduces the value needed for the cathode bypass caps by increasing RL.
Those caps need to be increased about ten-fold, and I think that is the reason for some midrange raspiness at this point. I hope so.
Also, since the first two plate chokes are only rated for 10ma and are flowing 13.2, I worry about saturation. How would nickel lams change the sound here (assuming new chokes rated at 15ma or so)?
Third, is there a way to try nickel lams in place of the cobalt ones for the output trannies? As shown on the prints, frame height is 1-5/16" with 2 inches between bolt hole centers.
Last, there just seems to be way too many capacitors in this design. Any ideas on trimming some out without losing sound quality?
TIA,
Len
Finally got around to it: Here are the present and proposed preamp schematics that pertain to magnetic upgrades.
All in all, the pre is working but with a few problems. Firstly, upon replacing out the last 380 uF electrolytic cap in the HT PS with a 100uF oiler, ripple rose from 0 to 12mV and it is clearly audible, as it gets in the way of the phono stage. That should get cleared up by the HT PS change shown, ie. putting a new nickel(?) choke between the 100 mike and 30 mike caps. While we're at it, might as well change the 80 rectifier to 5ar4, bringing up the voltage, which slightly reduces the value needed for the cathode bypass caps by increasing RL.
Those caps need to be increased about ten-fold, and I think that is the reason for some midrange raspiness at this point. I hope so.
Also, since the first two plate chokes are only rated for 10ma and are flowing 13.2, I worry about saturation. How would nickel lams change the sound here (assuming new chokes rated at 15ma or so)?
Third, is there a way to try nickel lams in place of the cobalt ones for the output trannies? As shown on the prints, frame height is 1-5/16" with 2 inches between bolt hole centers.
Last, there just seems to be way too many capacitors in this design. Any ideas on trimming some out without losing sound quality?
TIA,
Len