29-07-2020, 06:41 PM
(This post was last modified: 29-07-2020, 06:42 PM by Mike Watterson.)
Actual figures on data sheets in pF:
Cg1 (DK96, 1L6, 1j24b) = (3.9, 2.2, 3.2)
Cg2 (DK96, 1L6, 1j24b) = (4.8, 2.6, ?)
CRf (DK96, 1L6, 1j24b) = (7.4, 7.5, 3.2) (DK96, DK92 and 1L6 use the same pin but grid number differs)
Ca (DK96, 1L6, 1j24b) = (8.1, 7.0, 2.5*)
(* figure to g3 not quoted)
I remembered eventually when I went to get the two Invicta Radios from the loft. The IFTs had to be retuned!
Curiously my meter tells me that the variable cap I added to the IF anode of the 1j24b Pentode mixer is set to 8.5pF.
Thing is we don't know how Philips, Sylvania, RCA or the Russian Rod people actually measured the capacitance?
Anode to g2 and g3 is going to be miniscule on the Rod tubes, Four tiny rods for each.
The g1 to cathode filament is significant, about the same as 1L6 as the g1 is two plates very close to the filament.
So working very well with EXTRA capacitance!
I'll measure the likely important electrode capacitances on an 1L6 in a way that makes sense to me, in terms of how it would affect IF, LO and RF tuning,
The Anode is least problematic as it's one adjustment on one IFT coil for all bands that's simple. Obviously a 6.8pF, 7.5pF or 8.2 pF needs added between 1j24b mixer anode and 0V screen can.
The triodised 1j24b as an oscillator may be close enough for 1L6 or DK96.
The Pentode mixer probably has a lower capacitance and maybe a 3.3pF is needed so higher bands RF tuning isn't affected.
Cg1 (DK96, 1L6, 1j24b) = (3.9, 2.2, 3.2)
Cg2 (DK96, 1L6, 1j24b) = (4.8, 2.6, ?)
CRf (DK96, 1L6, 1j24b) = (7.4, 7.5, 3.2) (DK96, DK92 and 1L6 use the same pin but grid number differs)
Ca (DK96, 1L6, 1j24b) = (8.1, 7.0, 2.5*)
(* figure to g3 not quoted)
I remembered eventually when I went to get the two Invicta Radios from the loft. The IFTs had to be retuned!
Curiously my meter tells me that the variable cap I added to the IF anode of the 1j24b Pentode mixer is set to 8.5pF.
Thing is we don't know how Philips, Sylvania, RCA or the Russian Rod people actually measured the capacitance?
Anode to g2 and g3 is going to be miniscule on the Rod tubes, Four tiny rods for each.
The g1 to cathode filament is significant, about the same as 1L6 as the g1 is two plates very close to the filament.
So working very well with EXTRA capacitance!
I'll measure the likely important electrode capacitances on an 1L6 in a way that makes sense to me, in terms of how it would affect IF, LO and RF tuning,
The Anode is least problematic as it's one adjustment on one IFT coil for all bands that's simple. Obviously a 6.8pF, 7.5pF or 8.2 pF needs added between 1j24b mixer anode and 0V screen can.
The triodised 1j24b as an oscillator may be close enough for 1L6 or DK96.
The Pentode mixer probably has a lower capacitance and maybe a 3.3pF is needed so higher bands RF tuning isn't affected.