[Amps] GS35B Idle current increasing

[Paul Baldock]

Today I measured the filament voltage which is 13.5V. Spec is 11.9 to 
13.3, so I think this OK.

At 08:50 PM 3/13/2018, Jim Thomson wrote:
  I suspect the tubes available these days are all pulls or pulls of pulls

Jim - They have the appearance of unused NOS, still in the original packaging.

- Paul




>Date: Thu, 08 Mar 2018 09:09:00 -0800
>From: Paul Baldock <paul at paulbaldock.com>
>To: amps at contesting.com
>Subject: [Amps] GS35B Idle current increasing
>
><I built a GS35B amp a few years back to be used with my home brew AM
><rigs. Initially I set the idle current at around 110mA/4KV requiring
>about -35V bias. Over a few years of very little use the idle current
>drifted up so I increased the bias voltage to get it back down.
>Eventually I was up to -55V with the idle current at around 180mA,
>and so I installed another tube (purchased at the same time as the
>first). Same deal as before, started at -35V, now at -55V.
>
>Is this 2 bad tubes, or could I be doing something wrong? I'm getting
>ready to install a third tube purchased from a different source.
>
>- Paul KW7Y
>
>##   dunno about indirectly heated tubes.... but looking at eimacs tech notes
>for directly heated tubes, its normal for  idling current to 
>increase, as the tube
>approaches the normal end of its life span.   Your tube is not being 
>overdriven,
>thats not the issue here.   I suspect the tubes available these days 
>are all pulls,
>or pulls of pulls.    And if you try and increase 
>the  filament  voltage even more,
>the idle current will also increase somewhat.
>
>Jim  VE7RF
>
>_______________________________________________
>Amps mailing list
>Amps at contesting.com
>http://lists.contesting.com/mailman/listinfo/amps