Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: eleventeen on January 29, 2014, 04:12:10 pm
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Here are two possibilities, and maybe this can only be determined by building & measuring. But this is potentially useful because sometimes doublers make many more volts than we would want.
In ckt #1, I would imagine that the choke would seriously whack the pulsating DC out of the top diode and would very noticeably reduce the ultimate B+ available at the output.
In ckt #2, the choke is only attacking conventional ripple, much like a capacitor-input filter after a FW rectifier.
I think I have to build and check this.
(http://i172.photobucket.com/albums/w32/ttm4/dub_1_zps5595ff94.jpg)
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To me option 2 is correct
Consider the doubler as a standard bridge or Full Wave rectifier
and connect the choke at the same place
with the choke position like in 1
there is an unbalance on the doubler and I doubt this will be a positive effect
K
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But option #1 is possibly very useful, whether or not it is "correct"...because often when using salvaged power transformers, you wire it up and find B+ to be 70-150 volts too high, or more. There's no elegant way to get rid of 70-150 volts at 100 mils without large, heat-producing resistors or SS parts requiring a heatsink. Not that those take up more room than a choke....
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I vote for #2.
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To me option 2 is correct
Consider the doubler as a standard bridge or Full Wave rectifier
and connect the choke at the same place
with the choke position like in 1
there is an unbalance on the doubler and I doubt this will be a positive effect
K
I agree. With #1 the choke reduces the ripple for the top capacitor but does not effect the bottom one. I think there will be a net dc developed in the transformer causing some saturation. That is my have baked opinion as thinking it through is making my head ache. As they say, one quick test is worth ten theories.
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> Where do you put a choke in a voltage doubler?
Where do you put a buggy-whip in a modern car?
Voltage doublers have many features, but a main thing is that they are cheaper.
So why load it up with iron?
Especially choke-input, where the choke needs to be near as big as your PT.
Your "A" is perhaps a worst of all choices. At least put the choke where it gets BOTH sides of the AC wave and the flux will tend to reset, my "A" below. This gives an easy load to the PT. But the amount of iron in the choke would buy a bigger PT to take the surges cap-input.
"B": Draw the WHOLE circuit. A choke-output power supply does not make sense for most amplifier topologies. You gonna need an output cap. My "B" below.
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You are talking about a design ideal and I am talking about a situation where you have an existing say 250-0-250 power transformer. Problematical as in "can't get there from here". Full wave rectified via SS diodes produces something in the 350 volts range and with a tube rectifier you're not really there. Via a doubler you might see well north of 500 volts and before you pooh-pooh that I have 145 volts AC into a voltage doubler in the next room producing 373 volts and adding a 25 volt winding in series with my 145 VAC produces 456 volts. So a "doubler" is almost a "tripler" with an output: input factor of about 2.65. So with your 250-0-250 tranny, usable but technically inadequate for a dual 6L6 situation where you'd like to see minimum 400 volts, half your HV winding of your 250-0-250 could get you 660 volts. And you'd then be stuck with a lot more volts than you really want that you then have to turn into heat.
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> So a "doubler" is almost a "tripler"
Cap-input, the ideal factor is 2.828.
Choke-input, 1.8.
You never get to these values with actual parts. 2.65 is a reasonable realistic result.
Sorry if I pooh-poohed.