Ways to Lower B+ in a Tube Rectifed PS - diyAudio
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Old 27th March 2006, 06:13 PM   #1
waynev is offline waynev  Canada
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Default Ways to Lower B+ in a Tube Rectifed PS

Would like to dicuss methods of lowering B+ in a tube rectified power supply. Here are some methods - was wondering what are the pros and cons of each/some of them.

1) very small cap (.5u - 1.0u) as the first cap right after the rectifier
2) very small value resistor (.22 - .6 ohms) in one of heater legs of the rectifier
3)resistor in series with legs of trans secondary and rectifier anodes
4) resistor in series with B+ high voltage rail


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Old 27th March 2006, 06:31 PM   #2
Sherman is offline Sherman  United States
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How about just adding an RC section to the B+ filter? Lowers B+ and reduces ripple in the process.
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Old 27th March 2006, 06:34 PM   #3
rdf is offline rdf  Canada
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Or use a different rectifier tube.
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Old 27th March 2006, 07:21 PM   #4
fredl is offline fredl  United States
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You can put a resistor or zener diode between the center tap of the secondary and ground. You can also use this for a bias supply.

There is a very good article on this at Aiken Amplification. Look for "What is Back-Biasing?" on the advanced tech articles page.

http://aikenamps.com/

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Old 27th March 2006, 07:44 PM   #5
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i think the options are:

series resistance
zener dropping
choke input filter
regulation

IMHO, for SE or PP class A, series resistance is probably the way to go since you don't have to worry as much about regulation of the supply since current is essentially set.

For PP AB, then regulation is an issue, so choke input (or a modified CLC with a very small input cap), zener dropping (either series or in the cenbter tap of the PT) or regulation iare the best ways to avoid sagging the B+ rail on heavy transients.
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Old 27th March 2006, 08:39 PM   #6
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Hi waynev,

Quote:
Would like to dicuss methods of lowering B+ in a tube rectified power supply. Here are some methods - was wondering what are the pros and cons of each/some of them.
As usual, it depends, except for 2), which really has no virtue at all except lowering B+ "somehow", but at the gross expense of the pitiful rectifier tube.

So, please give more information on the circumstances, like what is fed by that PSU.

This is important, since, for example, a RIAA stage has completely other PSU requirements than a power stage running in class AB (or even mostly B).

Tom
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Old 27th March 2006, 11:20 PM   #7
waynev is offline waynev  Canada
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phono stage
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Old 28th March 2006, 04:25 AM   #8
lndm is offline lndm  Australia
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Pros/cons?

1. only used to 'tune' a choke input filter, not optimum IMO.

2. bad idea.

3. only necessary to reduce peak currents through rectifier (such as when you use high value first cap or if rectifier is old and weak). A small value is always good for damping resonances though.

4. This is the way to go, or more exactly, an extra RC. Regulation is also good/better (as mentioned already)
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Old 28th March 2006, 09:02 AM   #9
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Quote:
Originally posted by waynev
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Like others suggested already, in this case I would add another RC filter to the chain.

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