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waynev 27th March 2006 05:13 PM

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


...

Sherman 27th March 2006 05:31 PM

How about just adding an RC section to the B+ filter? Lowers B+ and reduces ripple in the process.

rdf 27th March 2006 05:34 PM

Or use a different rectifier tube.

fredl 27th March 2006 06:21 PM

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/

fred

aletheian 27th March 2006 06:44 PM

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.

Tubes4e4 27th March 2006 07:39 PM

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

waynev 27th March 2006 10:20 PM

phono stage

lndm 28th March 2006 03:25 AM

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)

Tubes4e4 28th March 2006 08:02 AM

Quote:

Originally posted by waynev
phono stage
Like others suggested already, in this case I would add another RC filter to the chain.

Tom


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