A-9C

[Richard Post]

Hi Jacques,

The "power resistor in the heater circuit" is the input resistor to the
high voltage electrolytic cap.  It is 340 ohms.  The markings are likely
burned off since this resistor gets quite hot even at the correct current
draw for the push-pull 6L6GC tubes running class AB1.  I had one that was
about 10 ohms high and replaced it even though it was well within tolerance
(10%).  Replacement was with two separate resistors that added up to the
correct resistance but spread the heat so that the rating was an equivalent
of about 25 watts.  The resistor is important to the filtering circuit.
The chassis metal nearby heats up considerably.  Be careful how and where
you mount this resistor.

I replaced the input caps to the 6L6 grids to assure that the bias was not
affected by cap leakage.  Check the cathode resistor to the 6L6 tubes for
correct value.  You can measure the voltage drop across the cathode
resistor to determine the current draw for the tubes.

Obligatory note:  High voltage in there!

Rich


>
>Is it possible to obtain the correct value for the power resistor
>which is used in the heater circuit of the 5V4G rectifier tube
>of the A-9C amplifier?
>
>Many thanks
>
>Jacques
>
>
>Jacques Carrier  [Electronics Tech.]
>Edouard-Montpetit College
>Electronics Dept. (TGE)
>945 Chambly  Rd.
>Longueuil (Quebec)
>CANADA   J4H 3M6
>Phone: 450-679-2631  EXT:586#
>Fax  : 450-679-5570  EXT:586
>Email: jcarrier at collegeem.qc.ca

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