Paul P wrote:
Does anyone have a guess what value choke L112 found here
http://www.ppinyot.com/hammarlund.ht...Supply%20Choke
might be? I am getting a 190 ac volt drop across this puppy. It has a cold
DC resistance of 97 ohms. How I got there is also explained at the
hyperlink page above.

The short of it is, the negative bias voltages are down across all
associated tubes that share that supply. Google is no help.


Hi,

I checked the L112 choke in my HX-50, and it is 75 Ohms d.c. resistance.
That is in the ball park of your 97 Ohms measurement.
That same choke also serves as the high voltage choke,
since it is in the common center tap return for the medium voltage
and H.V. taps as well as the bias tap.

In standby, I measure 195 VAC across the choke.
So, it sounds like your choke is innocent of the low bias
readings.

Have you put a scope across the bias supply capacitors C176 and C177?
They may need changing out if there is excessive ripple.
The 680 Ohm resistor in series with the bias supply may have increased
value.
Did you check the value of R142 and bias adjust pot R143? They may be
dragging down the bias voltage.

You might measure the bias voltage with the 6DQ5 final tube removed.
If the tube is gassy, it would tend to put a + voltage
on its control grid, which may be working backward
in your bias supply, making the supply less negative.

73,
Ed Knobloch