Pre PS Improvements?

[Bryan]

Hey Guys,

I've fooled around with some schematic software (TubePad) and have an initial schematic of my PS. I was wondering if anyone would like to make any suggestions to better the design???

Thanks,

Bryan

[mig-ru]

With your setup I dont see a need for a FWB, its a lot of current waste when using the voltage regulators. I think just using the 12AX4 as full wave rectifier with a cap input is sufficient.

[Bryan]

I know this is overkill , but I would like any opinions on my fillament supply. Would simpler be better in this case?

Thanks,

Bryan

[fdegrove]

Hi Bryan,

The PS looks O.K.
I would use a series reg myself followed by the shunt reg but that's just me.

Also, I suspect the Ox2 series of glowdischarge tubes to be quieter than their octal counterparts. It's a hunch though.

As for the heater supply, the CM choke does a better job when put in between the FWB and the first filter cap IME.

Cheers,

[Bryan]

Frank,

Thanks for the advice.

I will try the CM choke after teh bridge.

As for the series regulator, do you have any favorite method and/or schematics that would assist me? I was thinking about putting a CCS infront of the VR tubes. Is this what you have in mind?

Bryan

[fdegrove]

Hi,

I was thinking about putting a CCS infront of the VR tubes.

If you're 12B4As are plate loaded by a resistor and you want to replace that with a CCS then I would put the CCS after the VR tubes.
It will than also reject any residual noise from the PS and VR tubes.

I understand this is for a linestage but what circuit do you have in mind?

Cheers,

[Bryan]

Frank,

This is the preamp circuit as it stands now. The whole linestage (PS, fillaments, audio circuit) are as shown with the above and below schematics. I'm still chasing a little hum, which I expect is due to either layout or the volume pot....

Series regulator in the PS eh?

[fdegrove]

Hi,

Series regulator in the PS eh?

No need for it really....
You have the chokes which are way overdimensioned but I guess you know that already and the VR tubes operating as a shunt reg.
Nice PS in anyone's book, I think.

What does worry me but it's probably just a drawing mistake, is the 490R resistor as the gridleak on the 12B4A.

Surely that should read 470K or thereabout?

Also keep in mind that volpots really don't like DC on their wiper so either a switched attenuator or coupling cap are the safer solutions.

Cheers,

[Bryan]

Thanks for pointing that out Frank. The grid-leak and the output bleeder are both incorrect. I have fixed the values.

I know the chokes are on the big side. They are rated at 20H 100mA. If I am only drawing a total of 45mA through the PS, would the total inductnace of the chokes be lower?

[fdegrove]

Hi,

If I am only drawing a total of 45mA through the PS, would the total inductnace of the chokes be lower?

Fortunately not.

Cheers,