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Re: Unreg or reg PSUs ? any improvment ?!

Posted by Legendre (A) on February 25, 2005 at 08:24:59

In Reply to: Re: Unreg or reg PSUs ? any improvment ?! posted by Coresta on February 24, 2005 at 15:09:31:

>I'd like to regulate these input and driver stages with OA2 / OB2 gas reg tubes . For output stages , that's my question : do i go this way or not ?!

Assuming you are using the 0A2 / 0B2 in a simple shunt regulator, this is not possible for the output supplies. Maximum current avaialble from a simple shunt regulator is limited by the maximum steady-state current of the shunt device (gas-discharge tube, in this case).

For an 0A2/0B2, this maximum current is in the tens of mA, not the several amps that a 10-tube 6080 output section can draw.

As with any shunt regualtor, once this maximum current is breached, the output impedance of the supply rises exponentially - a simple function of the current-limiting device (resistor) used to bias the regulator.

> I could // some hi current transitors as ballast but your answer make me think it would not be easy nor useful to lower the internal impedances of supply rails .

Atma-Sphere output sections were traditionally 'cutthroat' affairs; full-wave bridge directly feeding a large bank of capacitors. This required relatively large values of capacitance, but this was fine as large values were needed to supply the large instantaneous currents required to play real music.

Even in this original configuration, the output was very quiet, partially due to common-mode noise cancellation in the circlotron output stage.

Today, little has changed, save the addition of a 1ohm 5w resistor which is used to create a simple C-R-C pi filter. The resistor provides a little additional quieting, and makes the output supplies slightly kinder to the transformer & rectifiers.

I'm not sure why Ralph was concerned with an C-L-C filter in the output; the only real concern I have, is that the DC resistance of the choke needs to be quite low.. on the order of 1ohm or less. Coupled with the large currents required, you would have some truly massive magnetics.

As for Harvey Rosenberg's writings on these subjects, I'd tend to take them with a grain of salt. I don't like to speak ill of the dead, but trying to garner any real technical wisdom from one of Harvey's articles was the proverbial needle-in-the-haystack search. HGR had some amusing and entertaing writings (at times) but I'd view his techinical pronouncements as anecdotal, not as vetted theory & practice.

Bill

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