Tubes Asylum

replace 12au7 with 5687 in border patrol pre

151.228.85.245

Philmoses

I have a very early border patrol preamp.

It uses a cv4068 at the moment.

According to border patrol themselves it uses 12au7.

Now i have also seem the same early model border control preamp using a 5687.

So, can i swap the 12au7/cv4068 for a 5687?

Some info on the net say same pink config, others say not, etc.

Thanks for any help.

Follow Ups:

RE: replace 12au7 with 5687 in border patrol pre - thermionic addictions 03:58:14 12/05/21 (2)
The pin outs of the two tubes are very different, so no, not interchangeable.
- RE: replace 12au7 with 5687 in border patrol pre - Philmoses 04:29:49 12/05/21 (1)
  Thanks for the reply.
  
  Are they similar enough to swap the pin connections and use as a replacement?
  
  Or is that...how long is a piece of string?
  
  Thanks.
  - RE: replace 12au7 with 5687 in border patrol pre - Tre' 08:45:32 12/05/21 (0)
    The 5687 draws three times the heater current vs. the 12au7.
    
    The plate resistance is a lot different. The 5687 is 1500 to 3000 depending on operating point and the 12aut is 6500 to 7700 depending on operating point.
    
    The transconductance is different. 11.5k to 5.4k for the 5687 depending on operating point vs. 3.1k to 2.2k for the 12au7.
    
    To use a 5687 in a circuit designed for a 12au7 a lot of changes would have to be made.
    
    A 6cg7 would be a much better fit.
    
    Tre'
    
    Have Fun and Enjoy the Music
    "Still Working the Problem"

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