Consider a 12JB6 They are the same in all respects except for cost, availability, and a simple filament wiring change.
Good luck, George
At 07:07 AM 12/18/05, you wrote:
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 neutralizationI 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]
