gwt <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Out of curiosity, since I own 3 sets of Drake twins, I checked to see
how much you could get 12JB6's for.
I found that you could buy two of them and have them matched for $38.50,
from
Antique Electronics Supply.
A decent deal, if you don't mind changing the heater wiring.
And a lot better price than the price quoted at RF Parts.
The price for 6JB6's was a bit cheaper than RF Parts, and the 1.25 per
tube for matching is a LOT cheaper than RF Parts.
You could get two matched 6JB6's from Antique Electronics for about $50
bucks.
George KE4HJ
George KB2Z wrote:
Karl,
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 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]
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