Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: gtrbryan on September 01, 2012, 11:49:49 pm
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I have an old PA that I converted into a champ with lots of bells, whistles and switches. The PT is 360 secondary for 110v. I'm getting about 485. I am using a 5Y3 and am getting more volts out of it than I would expect. I'm going to try another 5y3 and see if it brings it down.
If I need to knock it down further, I have a 200 ohm 25 watt resistor. Anyone see any problems in putting that between the 5y3 and the first filter cap?
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Resistor will give too much sagg and voltage will vary with power output. Better use some Zener diodes ( 10 volts , 5 watts at $0.50 each ) .
You put some in series with the center tap ( B + ) on your power transformer,
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If the amp is an SE, no much worry about SAG
K
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Yes , but only if the amp work in ( real ) class A.
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Yes , but only if the amp work in ( real ) class A.
His amp is SE Champ type, it has to work in real class A.
Brad :icon_biggrin:
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Nevertheless, if you can't lower it with a proper 5Y3GT rectifier, then some reverse-biased zeners in series with the HT winding's CT and the ground are the simplest way to go. Use 9V, 12V, or 15V zeners with a 5W rating, and put them in series (banded end(s) pointing to ground)
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Yes , but only if the amp work in ( real ) class A.
His amp is SE Champ type, it has to work in real class A.
Brad :icon_biggrin:
No , We have to check bias to say . Class A is not only a cathode with a resitor . Tube should operate at a very high current too. Resitor and tube must be matched.
That 's why I write " a real Class "
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Nevertheless, if you can't lower it with a proper 5Y3GT rectifier, then some reverse-biased zeners in series with the HT winding's CT and the ground are the simplest way to go. Use 9V, 12V, or 15V zeners with a 5W rating, and put them in series (banded end(s) pointing to ground)
This is my opinion too : ......the simplest way