Hammond AO-59-1 similaar to Mk III

Hello from a newbie.
The Dynaco specifies a 70mA idle current per output tube by measuring the voltage at the cathode resistor.
The Hammond schematic shows grounded cathodes for the outputs, so I assume bias is checked by measuring the OT resistance and plate voltages to calculate current? Should I look for 70mA  on this amp as well? Is the 15k fixed resistor in the bias supply tweaked to make it so?
Thanks, everyone.

I would add a 10 ohm resistor in the cathode chain, then measuring the current will be as easy
as measuring the voltage across this resistor. ( or two if you want to use unbalanced tubes )

The schematics has a fault ; there is a bias balance pot but no adjustment of the total voltage.

Here's my midnight analysis of the this topic:

This is a link to document, Hammond Grand 100, part 3, pages 29-31, that I use as the reference for my discussion:
http://theatreorgans.com/hammond/faq/g100/Hammond%20Grand%20100%20service%20manual%20Part%203%20pages%2029-31%20(amplifiers).pdf

It is clear that the Hammond AO-59 is a custom version of the Dynaco MKIII and the Hammond AO-58 is a custom version of the Dynaco ST70. Now weather Dynaco manufactured
the amps themselves or contracted out to 3rd party manufactures is as far as I can see is unknown, very common practice even back then.
I am confident that the Hammond procurement dept and the service departments had the Dynaco Amps as authorized substitutes for the Hammond Versions.

The Power and Output Transformers are variants of the original
Dynaco versions in that the output transformers have a single 8 ohm output and the power
transformer has lower voltage bias taps. I am of mind that using a bias balance pot instead of a bias level pot was a intentional design choice.
Looking at the AO-59 Schematic, the negative bias voltage of -54v is listed. (If this had been a Dynaco transformer it would have been -77v).
If you calculate the equivalent resistance of all of the bias resistors and then the voltage at the KT88 grids will be -43.7v, about right for a 70ma current bias per tube.
I don't know why this design decision was made except it could be the company's "way of doing things". It could be they would not have to buy matched pairs of tubes and
as long as the tubes meet the specs and the ruggable tubes back then they would be OK.
I believe that there is a cathode resistor and the schematic is mistaken because if you look at the AO-58 schematic a 10 ohm resistor is there.

On a side note, since the AO-59 does not use a pwb assembly for the driver circuit, i would love to see a picture of the inside of chassis
to see if they used a turret/eyelet board and/or terminal strips in the assembly. I have always liked the looks of a well crafted terminal strip assembly.

Thank you for the replies! One area I am concerned about is the feedback loop. Dynaco uses 1K/750pF, while Hammond uses only 680 ohms, and off the (only) 8-ohm tap. Dynaco uses a 390 pF tapped from the output screen, while Hammond uses none. I can duplicate the circuit but what RC combination is needed off the 8-ohm tap? (BTW I'm considering a purchase, and jwb, you will get your picture).

Check this thread. I also believe the 680 ohm off 16ohm tap was for safety. Ie run amp with no load or something happens with speaker
https://dynacotubeaudio.forumotion.com/t5170-nfb-resistor

1. The bias circuit is quite functional and is capable of compensating for the asymmetry of the output stage.
For tuning, you can use a temporary resistor in the cathode circuit, or a transition lamp panel.
2. The feedback circuit, as applied to different manufacturers of the output transformer, is determined by the general characteristics of the audio path and is specified during the tuning process.