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Old 30th January 2013, 08:36 PM   #1
mbeards is offline mbeards  United States
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Default Regulated Vs Non-regulated linear Power Supply

Hi Everyone,

I wanted to open a thread to get some real world opinions on usage of regulated vs non-regulated HT tube power supplies for Hi-fi amplifiers since I do not have much experience in using regulated supplies with tubes.

Regulated obviously has the advantaged of fixed HT voltage over wide current draw and rejection of ripple of the incoming voltage to the regulator, thus less complicated filters.

I mainly see two methods of regulation. A simple zener on the output of the power supply or, a MOSFET voltage follower with a zener to keep the gate fixed at a voltage below the peak power supply.

What are the benefits of these two regulated methods and their comparisons to non-regulated linear supplies in terms of transients, frequency response, and over amplifier “feel”?

Thanks,

Matt
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Old 30th January 2013, 09:43 PM   #2
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A lot depends on the application. I know very little about tube power amps so I cannot comment on them. When it comes to tube preamps, the first thing to remember is that without exception they are all class A with fairly small output signal levels. The means that any adequately decoupled stage draws an essentially constant current from the power supply. So long as the exact HT voltage at each stage is not critical, there is therefore no real need for a regulated HT voltage.

Regulators do provide a convenient way of reducing ripple but they can be quite noisy and may need further decoupling in very sensitive applications like microphone preamplifiers. In practice, about four stages of RC smoothing can can provide a very large reduction in ripple AND noise - around 120dB. The details were worked out by Scroggie about 70 years ago and are included in Morgan Jones' books.

Cheers

Ian
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Old 30th January 2013, 09:45 PM   #3
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One use could be a regulated screen supply, if you like pentodes. It can help the output tube have more power and a lower impedance.
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