Re: Another DC heater scheme

On Fri, 16 May 2008 06:45:22 -0500, "BretLudwig" <bratzirules@[EMAIL PROTECTED]
>
wrote:

> I suspect a simpler and quieter scheme would be to simply use a
>traditional linear regulator and pass transistor and a PT secondary of
>roughly suitable voltage. 

Of course. Or, put another way, you don't need it if circumstances are
such that it isn't needed. hehe

Same thing goes for cap multipliers.

I doubt you'd want to do it that way commercially but I needed at
least 4 different voltages and had a perfectly good 36VCT transformer.


> Alternatively, given a reasonably stable mains supply, just use a
>rectifier and filter.

You mean for the same circuit but without the transformer? Perhaps,
with a big enough current limiting resistor (transformer DCR limits
peak current) but you'd run into serious SOA problems with the
MOSFET... or large dissipation in the limiting resistor.

> Receiving tubes do not need or benefit especially
>from particularly precise heater voltages:

The problem wasn't 'precision'. It was needing 12.6V but having
something almost twice that.

> they do benefit from not being
>allowed to flow the full impulse current from cold on startup,

I have a soft start version too but I'm not convinced the 'full
impulse' is a significant problem.

> from
>keeping noise off the heater supply

You don't think 200mV DC ripple is better than a full 12.6VAC?

> and from having a reasonable
>heater-cathode offset.