[R-390] 6C4- 6C4WA- 6100- 6136

[Bryan Stephens]

Actually Essential Characteristics is a GE reference. Also, Sibley's Tube Lore has some interesting notes, and is a must-have for the boatanchor enthusiast's bookshelf.

      From: Bryan Stephens <bryanste at yahoo.com>
 To: "r-390 at mailman.qth.net" <r-390 at mailman.qth.net> 
 Sent: Wednesday, March 1, 2017 3:17 PM
 Subject: Re: [R-390] 6C4- 6C4WA- 6100- 6136
   
The Troubleshooting section of the R-390A manual advises not to substitute type 6C4W for a 6C4 tube:  "The differences in characteristics are such that the type 6C4W will not operate properly in the receiver." The 6C4's are used in the 1st, 2nd, and 3rd mixers.
Inter-plate capacitance varies among types 6C4, 6C4W (aka 6100), and 6C4WA (aka 6135). The 6C4W capacitances are higher than the 6C4 values, while the 6C4WA capacitances are lower. I think you want to avoid the 6C4W variant due to the higher inter-plate capacitance even though it's considered a premium tube. The 6C4W in mixer service may be prone to distortion or even oscillation. The 6C4WA/6135 is probably ideal, since it is a premium tube engineered for low inter-plate capacitance (although it does require a slightly higher heater current). See RCA Essential Characteristics for detailed specs.

73BryanKG4UPR

      From: "wb3fau55 at neo.rr.com" <wb3fau55 at neo.rr.com>
 To: r-390 at mailman.qth.net 
 Sent: Wednesday, March 1, 2017 9:19 AM
 Subject: [R-390] 6C4- 6C4WA- 6100- 6136
  
I need to buy some of these for my repairs.  I have read that I should not use 6C4WA?  Or can I use any of these in my R-390As?  Russ.
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