12-15-2013, 06:37 PM
Thanks Scott.
Well, as everyone can see some info in Rider's is wrong and what's more it is confusing as heck - the chassis drawing shows a backelite, the parts list shows a mica; or better yet that 35pF - 350pF question.
As for Q3 (350pF - 35pF) I looked at a very similar detector in 70, which uses a similar Pi-filter, and the values are 500pF and 250pF so I think I will go with 350pF in mine (no, I do not know the inductance, but I went with Ron's advice and bought 2.5mH one).
I ordered parts from Mouser, and they shipped Thursday, so I hope I will get them beginning this week.
Last thing I am kinda not sure of is that 1000pF cap from detector to the 1st Audio - the 1000 pF value will have about 1.5MOhm impedance at 100Hz which is a bit large, then again, I am not really a tube specialist so I do not know off the top of my head if it is bad or not. But out of common considerations that (and I do not have a datasheet for 27 tube) that say dynamic Miller capacitance is on the order of 100pF in some amp arrangement, the DC blocking capacitance should exceed it by more than that.
Do you think your 3903-J was factory installed?
Well, as everyone can see some info in Rider's is wrong and what's more it is confusing as heck - the chassis drawing shows a backelite, the parts list shows a mica; or better yet that 35pF - 350pF question.
As for Q3 (350pF - 35pF) I looked at a very similar detector in 70, which uses a similar Pi-filter, and the values are 500pF and 250pF so I think I will go with 350pF in mine (no, I do not know the inductance, but I went with Ron's advice and bought 2.5mH one).
I ordered parts from Mouser, and they shipped Thursday, so I hope I will get them beginning this week.
Last thing I am kinda not sure of is that 1000pF cap from detector to the 1st Audio - the 1000 pF value will have about 1.5MOhm impedance at 100Hz which is a bit large, then again, I am not really a tube specialist so I do not know off the top of my head if it is bad or not. But out of common considerations that (and I do not have a datasheet for 27 tube) that say dynamic Miller capacitance is on the order of 100pF in some amp arrangement, the DC blocking capacitance should exceed it by more than that.
Do you think your 3903-J was factory installed?
