Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Pochie45566 on January 12, 2018, 08:38:48 pm
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Whats the easiest way to lower b+ voltage. Just up the dropping resistors? It is tube rectified with a 5u4gb. and the voltage is a bit high for what i want.
Current voltage at nodes:
a: 495
b: 488
c: 439
d: 411
what I want:
a: 467
b: 390
c: 348
d: 334
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You could use a zener either off the B+ or on the PT ground. They will get very hot so use at least 15 watt, maybe two 15 volts in series between PT ground wire and chassis ground. That would drop the voltage 30 volts
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Easiest way is to start with a lower voltage PT.
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Easiest way is to start with a lower voltage PT.
best way to do that?
besides a variac. plus Node a is already close
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Are you sure the voltage is too high? There's a pretty good range of operational values; Once the circuit is operational the voltage may very well come down.
silverfox.
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Are you sure the voltage is too high? There's a pretty good range of operational values; Once the circuit is operational the voltage may very well come down.
silverfox.
I have a marshall 2204 that someone threw the PT of a sunn 200s into it, changed wiring and all. I wired it back to stock, Just need to drop the voltage to regain marshall tone.
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You could use a zener either off the B+ or on the PT ground. They will get very hot so use at least 15 watt, maybe two 15 volts in series between PT ground wire and chassis ground. That would drop the voltage 30 volts
\
so if I want to reach a specific voltage on each node, how do you say I do that?
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Put the correct PT back as sluckey suggested, the best way. The zener method will lower the B+, hence down the rail according to the dropping resistors, change them to what you want. But those zeners will get very hot and could blow, if you go with zeners use 15 watts and maybe use 10 volts in series to get desire B+ less likely to blow, use stand-offs and keep the lead lengths long when you string them, that will help cool them, no heat shrink and in a safe place away from any heat.
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I have a marshall 2204 that someone threw the PT of a sunn 200s into it, changed wiring and all. I wired it back to stock, Just need to drop the voltage to regain marshall tone.
Use the correct PT and get rid of that 5U4 (how did you get it in that chassis?). A 2204 wants silicon rectifiers. Should be about even money if you sell the Sunn PT. Heck, you may even come out ahead.
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I see that the Mark Huss 2204 drawing has the same voltages that you want and that what you call "node a" is the first node after the choke. If you are using the same convention for your Current voltages, I would surmise that you have a 1K resistor between a and b, a 10K resistor between b and c, and a 22K resistor between c and d. Try a 14K resistor between a and b, a 10K resistor between b and c, and a 10K resistor between c and d.
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I have a marshall 2204 that someone threw the PT of a sunn 200s into it, changed wiring and all. I wired it back to stock, Just need to drop the voltage to regain marshall tone.
Use the correct PT and get rid of that 5U4 (how did you get it in that chassis?). A 2204 wants silicon rectifiers. Should be about even money if you sell the Sunn PT. Heck, you may even come out ahead.
when they put the pt in, they converted the whole power section to sunn 200s
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I see that the Mark Huss 2204 drawing has the same voltages that you want and that what you call "node a" is the first node after the choke. If you are using the same convention for your Current voltages, I would surmise that you have a 1K resistor between a and b, a 10K resistor between b and c, and a 22K resistor between c and d. Try a 14K resistor between a and b, a 10K resistor between b and c, and a 10K resistor between c and d.
okay yeah ill do that, any wattage specifics for the resistors? 2w?
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Bottom of this page has got a good picture and some formulas that help you choose your dropping resistors:
http://www.valvewizard.co.uk/smoothing.html (http://www.valvewizard.co.uk/smoothing.html)
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okay yeah ill do that, any wattage specifics for the resistors? 2w?
2W for the 14K, 1W for the 10K between b and c, 1/2W for the 10K between c and d.