[3830] Bias & Alpha 91b

[Jeff Le Fouler - F6AOJ]

Hi,

a friend bring me an amplifier for repair :

ETO alpha 91b with a pair of GU74 new (not nos)

Screen circuit is now completely rebuit :

- all semiconductors and resistors replaced

- Fuse inserted in 430v 

in order to prevent a new pcb fire under resistors.

- 360v is now perfectly stable



Output power go up to 1500w,

but it require 100w input, usualy 50w do the job,

this is the last problem.



Bias circuits include 3 potentiometers :

- R61 Bias adjust

- R62 EBS adjust

- R41 EBS level

Depending of bias adjustments gain rise.

I am looking for a serious tunning procedure in order

to adjust correctly those interactive tunings.



There is nothing about that in the user manual,

and Alpha-Power provide no information at all

for over foreign customers.



Any help will be greatly appraciated.

73 

Jeff F6AOJ

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http://www.f6aoj.ao-journal.com/

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