Grounded grid preamp voltages

[nilsW]

I changed the resistors for R20 and R21 to 125R and 1.135k.

i now get 14.65 filament voltage. Before it was 16,9V. Can I live with 14.6V?

Could the regulator be faulty or the tubes?

I played some music on it and it sounds nice and is dead quiet.

 

[rayma]

You do need the proper 12.6V filament voltage, or the filament will likely to be damaged.
Change only the 1.135k resistor to adjust the voltage. Perhaps its value is a bit off, or else the regulator is off tolerance.

 

[nilsW]

Thanks Rayma, I measured the resistor before installing it. It was 1.134k. I will replace the regulator får peace of mind.

 

[rayma]

Something odd is definitely going on, but if the output is still too high, lowering the 1.134k resistor should work.
You can just add in parallel with it around 10k, adjusting the resistor value until the output is 12.6V.

 

[astouffer]

Maybe the regulator isn't a legit LT1085.

 

[rayma]

Oops, fake copy gives fake results.

 

[6A3sUMMER]

I think the circuit is a highly modified LTP phase inverter, with an extra stage tacked on.

The plate load of the driven triode grid of the LTP is Zero Ohms. That makes it a cathode follower.
The cathode follower drives the 2nd cathode of the LTP.
The LTP 2nd plate drives the 3rd triode (SRPP?).

True Grounded Grid Amplifiers always have the following 2 characteristics:
The Grid is DC terminated at Zero Ohms.
The Grid is AC terminated at Zero Ohms (And at RF too).
Anything else is either:
A Marketing Ploy to get you to purchase the product;
Or,
Has been named Grounded Grid by a Marketeer who is technically challenged.

Grounded Grid? . . .
Check out a 1956 ARRL Radio Amateurs Handbook.
Or Check out the 30MHz IF amplifier of a 10GHz Surface Search Radar that was on Year 1943 Fletcher Class Destroyers.

Some of those who do not know history are bound to repeat it . . . and might make things worse than they originally were.