21-10-2023, 08:54 AM
(This post was last modified: 21-10-2023, 08:56 AM by Mike Watterson.)
(21-10-2023, 08:31 AM)Kalee20 Wrote:(21-10-2023, 08:10 AM)Mike Watterson Wrote: Certainly real Pentodes are inherently noisier than Triodes, but the Rod Pentode is just electrostatic rod focusing, no spiral wire grids, so is much quieter.
I'd dispute that, though - g2 in the rod pentode does draw some current, so partition noise is possible.
It doesn't matter if g2 is rods, wire spiral, or perforated mesh - if it draws current, the noise mechanism is there!
(I'd concede that the current is less, proportionally, to anode current than in spiral grid pentodes, so the actual noise may be a few db less. But it's still there)
Yes, still noise. But Joe Sousa claims that in theory and practice it's less on a Rod Pentode than a regular kind. I've also no idea why the EF37 and EF86 were claimed to be low noise, but Jez is first person I've read claiming an EF86 isn't, or pointless. Maybe I could measure but I'd take Joe's statements.
I wrote "quieter", not quiet.
You get more noise from any electronic device than equivalent resistor, unless it's run in liquid nitrogen or something. Current noise figures on Ku Band LNBFs of 0.2dB are likely fantasy; they are probably cherry picking, also the difference between 1db and 0.2dB NF isn't very significant. You need a bigger dish if rain is an issue.
Similarly it's a truly rubbish HF receiver if receiver noise is an issue in last 30 years.
