Princeton OT - 6.2K instead of 8K - What will happen ?

[kagliostro]

The OT of the Ibanez TSA15H that is going to be converted in Fender 6g2 was measured

the primary is in the order of ~6200ohm

EDIT: instead of the 8k - 8.5k that has OT indicated as spare parts for the Princeton

The PT of the TSA15H has a mere 0-250v AC instead of 325v-0-325v AC

the problem about B+ can be solved using SS rectify and a SAG resistor

250v AC becomes 350v DC and the Princeton B+ is rated at 315v, so no problems about B+

but what about the low 6.2K impedance of the primary ?

What is better to do with this "low" primary impedance ?

is it better to don't use the SAG resistor as to use the whole 350v DC ?

I apologize for my naivety, I'm always at odds with tube curves  

Many Thanks

K

[mresistor]

Lots of folks use a deluxe OT in Princetons and Princeton Reverbs with not a problem. These usually have a 6600 ohm primary. Yours is only 400 ohm shy of that. I'd say it would work alright in a 6G2 circuit.

[kagliostro]

What I'm in doubt is if the standard Princeton -35v of bias is correct with this OT

less impedance isn't equal to more current with the same bias level ?

K

[kagliostro]

Knowing the tube max plate dissipation (12W for 6v6)

Knowing the B+ (315v)

Knowing I want to set the tube at 27mA each (70%)

knowing the OT impedance (6.2k)

there is a way to predict which will be the bias voltage to be set ?

K

[jazbo8]

It's about -40V with Vs at 312V per 6G2, see:

[Edit] Image removed due to operator error... 

Jaz

[kagliostro]

Thanks Jazbo8

My brain refuses to compute when there are tube curves

I'm still trying to convince it to understand 

K

[HotBluePlates]

The OT of the Ibanez TSA15H that is going to be converted in Fender 6g2 was measured

the primary is in the order of ~6200ohm

EDIT: instead of the 8k - 8.5k that has OT indicated as spare parts for the Princeton

The PT of the TSA15H has a mere 0-250v AC instead of 325v-0-325v AC

You are all over-thinking this.

The Ibanez originally used 2x 6V6, with its OT and PT. Use the same bias the original amp did.

It's about -40V with Vs at 312V per 6G2, see:

Yes, but you do know that in class AB, the idle operating point does not fall on the loadline, right?

It does in class A, because the tube is always on. Since the tube will cut off at some point in class AB, and the idle point is not at 0mA, the idle point will not be on the loadline.

[jazbo8]

Yes, but you do know that in class AB, the idle operating point does not fall on the loadline, right?

Doh! I should know, but obviously not well enough... Not only that I found the load line used was in-correct to begin with, better go back and hit the books...

TIA,
Jaz

[kagliostro]

You are all over-thinking this.

The Ibanez originally used 2x 6V6, with its OT and PT. Use the same bias the original amp did.

OK HBP, message received

Many Thanks

K

[mresistor]

You are all over-thinking this.

I'm sure I'm not guilty on that charge...   

[HotBluePlates]

Me too!