I've heard that there is a way to simulate the voltage drop of a lower-powered recto by installing a resistor in series with the recto currently in use in an amp.....that is, to take a tube like a 5AR4 and knock some volts off of the B+ line not by putting in a 5V4, or 5Y3, but just by wiring in a nice, sturdy power resistor. It sounds like a nice way to keep a recto with nice current handling abilities but then get some of the drop of a lower powered recto. Phil and I have been PM'ing each other about this and figured we'd just start a thread and see what you all know about it. For example, sometimes a 5V4 has just the right voltage drop, but not enough current handling capacity....
Anyway, I know this is vague, but so is my knowledge of most things amplifier...
krash wrote:I think putting a resistor in series with the diodes or rectifier in an amp to give a "sag" effect is pretty common is it not?
I use a resistor in series with ss diodes in my amps.
I don't know if it is common....that's why I was asking. I know we find various power resistors in the circuit after the initial cap in the power section, etc...but Phil mentioned putting something right off the recto.
What rating of resistor do you commonly use in this situation?
Figure out how much voltage you want to drop, add up the current of all your tubes at full output, multiply and go to the next biggest power rating. Just don't cut it close - go higher if necessary to get a cushion.
Figure out how much voltage you want to drop, add up the current of all your tubes at full output, multiply and go to the next biggest power rating. Just don't cut it close - go higher if necessary to get a cushion.
I might not be reading this right. I didn't think you would need such a huge resistor to provide a little drop here.
At any rate, it is fairly common practice, at least among modders. Ted Weber's "Copper Caps" work on this principle.
Figure out how much voltage you want to drop, add up the current of all your tubes at full output, multiply and go to the next biggest power rating. Just don't cut it close - go higher if necessary to get a cushion.
I might not be reading this right. I didn't think you would need such a huge resistor to provide a little drop here.
At any rate, it is fairly common practice, at least among modders. Ted Weber's "Copper Caps" work on this principle.
Who said huge? Just big enough to do the job. If it's just a little drop, then the added sag won't be noticeable, so there's not much sense in doing it. If you're simulating a tube rectifier, then you're talking 20-50V drop.
Some ballpark numbers:
6V6
50V x 100mA = 5W
Go up to 10W for the power rating.
6L6
17V x 210mA = 3.6W
Feelin' lucky? 5W resistor. I'd go to 10W - all your B+ passes through it all the time. Why skimp?
To restate Marks point. The power rating of the dropping resistor is based on the voltage drop ACROSS the resistor at the max current rating. As stated, not such a big deal.
FWIW
Dan
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
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Very cool. Thanks guys. The amp in question is an AC30ish circuit, and I'm running a 5AR4 in the recto spot. I'd just like to drop maybe 10-20v or so, and get things looking more like if I was running a 5V4.
Nice. Right now, at the first cap off the recto I'm seeing about 347v. Ideally, I'd like to have about 320v or so.... So, in that case, with an AC30-ish power section, wanting about a 20v drop, I'd need about a 100 ohm, 10w resistor, right?
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
dehughes wrote:Nice. Right now, at the first cap off the recto I'm seeing about 347v. Ideally, I'd like to have about 320v or so.... So, in that case, with an AC30-ish power section, wanting about a 20v drop, I'd need about a 100 ohm, 10w resistor, right?
Looking at the data sheet, it's more like 140mA for four EL84s at idle. The 200mA I cited above is under max. signal. So.....
