[drakelist] Neutralizing

[Karl Henrik Laache]

Hi group   I have tried different substitute PA-tubes for my T-4XB, because the 6JB6s are becoming quite expensive here in Norway.   The types tried are 6KM6, 6JF6 and 6GJ5.  But there seems to be a problem with neutralization of certain tubes.  Specifically the 6KM6 and 6JF6.  The 6GJ5s neutralizes ok, but output on 10 meters are low, 5-10 W.   The 6KM6 and 6JF6 are impossible to neutralize.   I looked in the compendium “Care and feeding of power grid tubes” by Eimac, and got a possible explanation and solution to this problem.   When using the formula foir single ended neutralization I got the necessary value for the neutralizing cap with the 6JB6 and 6GJ5 in the T-4XB would be 6.7pF, while the same formula used with the 6KM6 and 6JF6 would be 27.3pF.  The neutralizing cap in the t-4XB is 6 pF + 2.7-8.4pF.    My question to the group is:  Would it be possible to neutralize the 6KM6 and 6JF6 by adding a capacitor of 20pF to the C48/C49 in the T-4XB?  If not, why?       73's de LA1CU Karl email:  [EMAIL PROTECTED]