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1. [Amps] Runaway Plate Current (score: 1): Author: Roger <ai7rogerroger@gmail.com>; Date: Fri, 27 Dec 2013 22:16:18 -0800; Trying to finish up my 6m Junk Box Amp. Quad 4x150a's, 1700v anode, ~355vdc screen, ~ -55v bias. Input terminated in 50ohms, output terminated in 50ohms. Keying the amp with no excitation to adjust i; /archives//html/Amps/2013-12/msg00158.html (6,734 bytes)
2. Re: [Amps] Runaway Plate Current (score: 1): Author: "Gary Schafer" <garyschafer@comcast.net>; Date: Sat, 28 Dec 2013 15:14:30 -0600; Are the screens getting grounded when you remove the screen voltage? If not that will cause runaway plate current. 73 Gary K4FMX _______________________________________________ Amps mailing list Amps; /archives//html/Amps/2013-12/msg00159.html (8,312 bytes)
3. Re: [Amps] Runaway Plate Current (score: 1): Author: "qrv@kd4e.com" <qrv@kd4e.com>; Date: Sat, 28 Dec 2013 17:26:39 -0500; Working on an amp at 1:30 in the morning? ;-) Seriously, I'm guessing the cause will be on a very short list soon to be posted by the amp gurus here. I'm curious to learn the reason as well - not tha; /archives//html/Amps/2013-12/msg00162.html (8,497 bytes)
4. Re: [Amps] Runaway Plate Current (score: 1): Author: peter chadwick <g8on@fsmail.net>; Date: Sat, 28 Dec 2013 23:27:01 +0100; I sent basically the same comment four hours ago, but such are the marvels of the internet, it has disappeared. probably resurface ina couple of months..... But, yes, I totally agree with Gary. 73 Pe; /archives//html/Amps/2013-12/msg00163.html (9,028 bytes)
5. Re: [Amps] Runaway Plate Current (score: 1): Author: "Carl" <km1h@jeremy.mv.com>; Date: Sun, 29 Dec 2013 10:59:29 -0500; OTOH, the NCL-2000 simply removes the screen voltage and hasnt run wild since its 1963 inception and thousands sold. Im sure many other tetrode amps do the same. If the screen supply is switched at t; /archives//html/Amps/2013-12/msg00167.html (10,789 bytes)
6. Re: [Amps] Runaway Plate Current (score: 1): Author: peter chadwick <g8on@fsmail.net>; Date: Sun, 29 Dec 2013 17:14:57 +0100; The NCL 2000 used a pair of 8122s, I believe. The RCA data sheet says a maximum screen supply impedance of 10kohm for them and does not say that you can get negative screen grid current. The 4X150 ca; /archives//html/Amps/2013-12/msg00168.html (11,778 bytes)
7. Re: [Amps] Runaway Plate Current (score: 1): Author: Bill Turner <dezrat1242@wildblue.net>; Date: Sun, 29 Dec 2013 13:05:33 -0800; IMO, putting a tetrode into standby by removing screen voltage is bad design for the reason the original poster mentioned. Depending on the tube, even zero screen voltage may not put it all they way; /archives//html/Amps/2013-12/msg00170.html (7,587 bytes)
8. Re: [Amps] Runaway Plate Current (score: 1): Author: "Carl" <km1h@jeremy.mv.com>; Date: Sun, 29 Dec 2013 21:32:37 -0500; The NCL-2000 runs negative screen current during tuning as do most all ceramic tetrodes at least up to the 4CX1500B. Heavy bleeding took care of that in the old days. Using a tuning chart is one way; /archives//html/Amps/2013-12/msg00175.html (13,094 bytes)
9. [Amps] Runaway Plate Current (score: 1): Author: "Jim Thomson" <jim.thom@telus.net>; Date: Sun, 29 Dec 2013 23:12:25 -0800; IMO, putting a tetrode into standby by removing screen voltage is bad design for the reason the original poster mentioned. Depending on the tube, even zero screen voltage may not put it all they way; /archives//html/Amps/2013-12/msg00177.html (7,443 bytes)
10. Re: [Amps] Runaway Plate Current (score: 1): Author: Roger <ai7rogerroger@gmail.com>; Date: Sat, 28 Dec 2013 19:25:26 -0800; Thanks to all who replied and my apologies for double posting. It took a while for this to get posted to the Amps Reflector so I also asked the question on the eHam forum. The problem was resolved by; /archives//html/Amps/2013-12/msg00184.html (8,072 bytes)
11. [Amps] Runaway Plate Current (score: 1): Author: John Lyles <jtml@losalamos.com>; Date: Mon, 30 Dec 2013 22:58:24 -0700; This is what I do in amplifiers at work. One tetrode runs with 1200 VDC on the screen grid all the time, and 12 kV on the anode. Control grid is normally -250 VDC for quiescent current for linear amp; /archives//html/Amps/2013-12/msg00219.html (9,712 bytes)

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