[ARC5] GO-9 Project: Why the Resistor?

[J Mcvey]

 I'm not a tube circuit designer, but I suspect the resistor will reduce cathode emissions , thus plate current also for a given g1 voltage.In othe words they may have altered the tube characteristics to better suit the application . 
That begs the question "why not just a different tube"?...or maybe they were too committed to using that tube when they discovered they should be using less current there?Who knows? The answer died with the designers.
I repaired a BC348 with a home-brew power supply for poor performance by supplying the proper voltage to the tube filaments. The original supply was only supplying 18volts.the additional 8 volts made a big difference.

    On Tuesday, October 22, 2019, 4:19:47 PM EDT, Dennis Monticelli <dennis.monticelli at gmail.com> wrote:  
 
 Hmmm.  A cooler filament reduces grid emission, but that would only apply to circuits in which the grid resistance was very high.  Dunno what's going on here but it's certainly no accident.  There's a reason.
BTW, the filament will be above 10V because the 0.7A filament current only applies at 12.6V.
Dennis AE6C
On Tue, Oct 22, 2019 at 1:08 PM howard holden <holden7471 at msn.com> wrote:


I never paid much attention to that resistor, but I can tell you that for 10 years of heavy use my GO has used the same tube in the IPA, with no noticeable difference in performance. Maybe related to the 1K resistor in the filament CT R207? Dunno. BTW that's where I key my GO, between R207 and ground. You'd think that was a lousy place to key but it's not.





I've seen one or two places where a dropping resistor was used in an oscillator filament circuit, can't remember any off hand though, and no idea of why they'd do that.





Howie WB2AWQ

On 10/22/2019 12:28 PM, David Stinson wrote:


Dear Smart People:
Please take a look at the GO-9 transmitter schematic attached.  The 837 MO and 837 IA tubes are supplied filament voltage from the same buss.  However, the connection to the 837 IA tube goes through R-312, a 4.5 Ohm 20 Watt resistor (red arrow).  At the 0.7 Amp current of the 837, this is going to drop around 3 Volts, reducing the tubes filament voltage from 12.6 VAC 800Hz down to 9.6 V.  I haven't found a mention of this in the manual's circuit description.  Why would they do this?

TNX OM ES 73 DE Dave AB5S


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